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基于S3C2440的嵌入式Linux驱动——Framebuffer子系统解读_2440 framebuffer

作者：Gausst松鼠会 | 2024-02-11 15:58:33

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2440 framebuffer

本文将介绍Framebuffer子系统

目标平台：TQ2440 CPU：s3c2440

LCD设备：3.5英寸，分辨率320X240


1. 概述

Framebuffer，中文名字是帧缓冲，这个帧也就是一副图像所需要的数据。因此，帧缓冲其实就是LCD设备的驱动程序。Linux中，framebuffer子系统框架如下：


核心层的代码以fbmem.c为主，核心层包括许多与具体硬件无关的代码，并且提供了API给用户空间。用户空间使用系统调用，系统调用会使用相应的API函数，最后会调用驱动层实现功能。对于不同的设备，驱动层的代码将有所不同。

接下来的内容中，首先给出framerbuffer使用的数据结构；随后简单描述framerbuffer核心层；最后，针对S3C2440，对驱动代码进行分析。

2. 数据结构

2.1 fb_info 结构

  该结构是内核用于描述一个特定framebuffer设备。其中包含了几个重要的结构，将在下面介绍。

  下列代码位于include/linux/fb.h

  1. struct fb_info {
  2. 	int node;
  3. 	int flags;
  4. 	struct mutex lock;		/* Lock for open/release/ioctl funcs */
  5. 	struct fb_var_screeninfo var;	/* Current var */
  6. 	struct fb_fix_screeninfo fix;	/* Current fix */
  7. 	struct fb_monspecs monspecs;	/* Current Monitor specs */
  8. 	struct work_struct queue;	/* Framebuffer event queue */
  9. 	struct fb_pixmap pixmap;	/* Image hardware mapper */
  10. 	struct fb_pixmap sprite;	/* Cursor hardware mapper */
  11. 	struct fb_cmap cmap;		/* Current cmap */
  12. 	struct list_head modelist;      /* mode list */
  13. 	struct fb_videomode *mode;	/* current mode */
  14.  
  15. #ifdef CONFIG_FB_BACKLIGHT
  16. 	/* assigned backlight device */
  17. 	/* set before framebuffer registration, 
  18. 	   remove after unregister */
  19. 	struct backlight_device *bl_dev;
  20.  
  21. 	/* Backlight level curve */
  22. 	struct mutex bl_curve_mutex;	
  23. 	u8 bl_curve[FB_BACKLIGHT_LEVELS];
  24. #endif
  25. #ifdef CONFIG_FB_DEFERRED_IO
  26. 	struct delayed_work deferred_work;
  27. 	struct fb_deferred_io *fbdefio;
  28. #endif
  29.  
  30. 	struct fb_ops *fbops;
  31. 	struct device *device;		/* This is the parent */
  32. 	struct device *dev;		/* This is this fb device */
  33. 	int class_flag;                    /* private sysfs flags */
  34. #ifdef CONFIG_FB_TILEBLITTING
  35. 	struct fb_tile_ops *tileops;    /* Tile Blitting */
  36. #endif
  37. 	char __iomem *screen_base;	/* Virtual address */
  38. 	unsigned long screen_size;	/* Amount of ioremapped VRAM or 0 */ 
  39. 	void *pseudo_palette;		/* Fake palette of 16 colors */ 
  40. #define FBINFO_STATE_RUNNING	0
  41. #define FBINFO_STATE_SUSPENDED	1
  42. 	u32 state;			/* Hardware state i.e suspend */
  43. 	void *fbcon_par;                /* fbcon use-only private area */
  44. 	/* From here on everything is device dependent */
  45. 	void *par;	
  46. };

2.2 fb_fix_screeninfo结构

  该数据结构是不可改变的，也就是说用户空间不能改变该结构中的任何成员，在核心层我们将会看到这点。

  下列代码位于include/linux/fb.h

  1. struct fb_fix_screeninfo {
  2. 	char id[16];			/* identification string eg "TT Builtin" */
  3. 	unsigned long smem_start;	/* Start of frame buffer mem */
  4. 					/* (physical address) */
  5. 	__u32 smem_len;			/* Length of frame buffer mem */
  6. 	__u32 type;			/* see FB_TYPE_*		*/
  7. 	__u32 type_aux;			/* Interleave for interleaved Planes */
  8. 	__u32 visual;			/* see FB_VISUAL_*		*/ 
  9. 	__u16 xpanstep;			/* zero if no hardware panning  */
  10. 	__u16 ypanstep;			/* zero if no hardware panning  */
  11. 	__u16 ywrapstep;		/* zero if no hardware ywrap    */
  12. 	__u32 line_length;		/* length of a line in bytes    */
  13. 	unsigned long mmio_start;	/* Start of Memory Mapped I/O   */
  14. 					/* (physical address) */
  15. 	__u32 mmio_len;			/* Length of Memory Mapped I/O  */
  16. 	__u32 accel;			/* Indicate to driver which	*/
  17. 					/*  specific chip/card we have	*/
  18. 	__u16 reserved[3];		/* Reserved for future compatibility */
  19. };

2.3 fb_var_screeninfo结构

  该数据结构是可以改变的，也就是说用户空间可以改变该结构中的成员。该数据结构中的很多成员就由板级信息复制而来，在驱动代码中我们将会看到这点。

  下列代码位于include/linux/fb.h

  1. struct fb_var_screeninfo {
  2. 	__u32 xres;			/* visible resolution		*/
  3. 	__u32 yres;
  4. 	__u32 xres_virtual;		/* virtual resolution		*/
  5. 	__u32 yres_virtual;
  6. 	__u32 xoffset;			/* offset from virtual to visible */
  7. 	__u32 yoffset;			/* resolution			*/
  8.  
  9. 	__u32 bits_per_pixel;		/* guess what			*/
  10. 	__u32 grayscale;		/* != 0 Graylevels instead of colors */
  11.  
  12. 	struct fb_bitfield red;		/* bitfield in fb mem if true color, */
  13. 	struct fb_bitfield green;	/* else only length is significant */
  14. 	struct fb_bitfield blue;
  15. 	struct fb_bitfield transp;	/* transparency			*/	
  16.  
  17. 	__u32 nonstd;			/* != 0 Non standard pixel format */
  18.  
  19. 	__u32 activate;			/* see FB_ACTIVATE_*		*/
  20.  
  21. 	__u32 height;			/* height of picture in mm    */
  22. 	__u32 width;			/* width of picture in mm     */
  23.  
  24. 	__u32 accel_flags;		/* (OBSOLETE) see fb_info.flags */
  25.  
  26. 	/* Timing: All values in pixclocks, except pixclock (of course) */
  27. 	__u32 pixclock;			/* pixel clock in ps (pico seconds) */
  28. 	__u32 left_margin;		/* time from sync to picture	*/
  29. 	__u32 right_margin;		/* time from picture to sync	*/
  30. 	__u32 upper_margin;		/* time from sync to picture	*/
  31. 	__u32 lower_margin;
  32. 	__u32 hsync_len;		/* length of horizontal sync	*/
  33. 	__u32 vsync_len;		/* length of vertical sync	*/
  34. 	__u32 sync;			/* see FB_SYNC_*		*/
  35. 	__u32 vmode;			/* see FB_VMODE_*		*/
  36. 	__u32 rotate;			/* angle we rotate counter clockwise */
  37. 	__u32 reserved[5];		/* Reserved for future compatibility */
  38. };

2.4 fb_ops结构

  该结构描述了用于fb_info的方法，这些方法中有些是要驱动程序提供的，而有些可以使用内核提供的方法。

 下列代码位于include/linux/fb.h

  1. /*
  2.  * Frame buffer operations
  3.  *
  4.  * LOCKING NOTE: those functions must _ALL_ be called with the console
  5.  * semaphore held, this is the only suitable locking mechanism we have
  6.  * in 2.6. Some may be called at interrupt time at this point though.
  7.  */
  8.  
  9. struct fb_ops {
  10. 	/* open/release and usage marking */
  11. 	struct module *owner;
  12. 	int (*fb_open)(struct fb_info *info, int user);
  13. 	int (*fb_release)(struct fb_info *info, int user);
  14.  
  15. 	/* For framebuffers with strange non linear layouts or that do not
  16. 	 * work with normal memory mapped access
  17. 	 */
  18. 	ssize_t (*fb_read)(struct fb_info *info, char __user *buf,
  19. 			   size_t count, loff_t *ppos);
  20. 	ssize_t (*fb_write)(struct fb_info *info, const char __user *buf,
  21. 			    size_t count, loff_t *ppos);
  22.  
  23. 	/* checks var and eventually tweaks it to something supported,
  24. 	 * DO NOT MODIFY PAR */
  25. 	int (*fb_check_var)(struct fb_var_screeninfo *var, struct fb_info *info);
  26.  
  27. 	/* set the video mode according to info->var */
  28. 	int (*fb_set_par)(struct fb_info *info);
  29.  
  30. 	/* set color register */
  31. 	int (*fb_setcolreg)(unsigned regno, unsigned red, unsigned green,
  32. 			    unsigned blue, unsigned transp, struct fb_info *info);
  33.  
  34. 	/* set color registers in batch */
  35. 	int (*fb_setcmap)(struct fb_cmap *cmap, struct fb_info *info);
  36.  
  37. 	/* blank display */
  38. 	int (*fb_blank)(int blank, struct fb_info *info);
  39.  
  40. 	/* pan display */
  41. 	int (*fb_pan_display)(struct fb_var_screeninfo *var, struct fb_info *info);
  42.  
  43. 	/* Draws a rectangle */
  44. 	void (*fb_fillrect) (struct fb_info *info, const struct fb_fillrect *rect);
  45. 	/* Copy data from area to another */
  46. 	void (*fb_copyarea) (struct fb_info *info, const struct fb_copyarea *region);
  47. 	/* Draws a image to the display */
  48. 	void (*fb_imageblit) (struct fb_info *info, const struct fb_image *image);
  49.  
  50. 	/* Draws cursor */
  51. 	int (*fb_cursor) (struct fb_info *info, struct fb_cursor *cursor);
  52.  
  53. 	/* Rotates the display */
  54. 	void (*fb_rotate)(struct fb_info *info, int angle);
  55.  
  56. 	/* wait for blit idle, optional */
  57. 	int (*fb_sync)(struct fb_info *info);
  58.  
  59. 	/* perform fb specific ioctl (optional) */
  60. 	int (*fb_ioctl)(struct fb_info *info, unsigned int cmd,
  61. 			unsigned long arg);
  62.  
  63. 	/* Handle 32bit compat ioctl (optional) */
  64. 	int (*fb_compat_ioctl)(struct fb_info *info, unsigned cmd,
  65. 			unsigned long arg);
  66.  
  67. 	/* perform fb specific mmap */
  68. 	int (*fb_mmap)(struct fb_info *info, struct vm_area_struct *vma);
  69.  
  70. 	/* save current hardware state */
  71. 	void (*fb_save_state)(struct fb_info *info);
  72.  
  73. 	/* restore saved state */
  74. 	void (*fb_restore_state)(struct fb_info *info);
  75.  
  76. 	/* get capability given var */
  77. 	void (*fb_get_caps)(struct fb_info *info, struct fb_blit_caps *caps,
  78. 			    struct fb_var_screeninfo *var);
  79. };


3. frambuffer核心层

首先来看下frmaebuffer子系统的初始化函数。

3.1 fbmem_init和fbmem_exit

下列代码位于drivers/video/fbmem.c

  1. /**
  2.  *	fbmem_init - init frame buffer subsystem
  3.  *
  4.  *	Initialize the frame buffer subsystem.
  5.  *
  6.  *	NOTE: This function is _only_ to be called by drivers/char/mem.c.
  7.  *
  8.  */
  9.  
  10. static int __init
  11. fbmem_init(void)
  12. {
  13. 	proc_create("fb", 0, NULL, &fb_proc_fops);
  14.  
  15. 	if (register_chrdev(FB_MAJOR,"fb",&fb_fops))		/*注册字符设备，major=29*/
  16. 		printk("unable to get major %d for fb devs\n", FB_MAJOR);
  17.  
  18. 	fb_class = class_create(THIS_MODULE, "graphics");	/*创建类*/
  19. 	if (IS_ERR(fb_class)) {
  20. 		printk(KERN_WARNING "Unable to create fb class; errno = %ld\n", PTR_ERR(fb_class));
  21. 		fb_class = NULL;
  22. 	}
  23. 	return 0;
  24. }
  25.  
  26. #ifdef MODULE
  27. module_init(fbmem_init);
  28. static void __exit
  29. fbmem_exit(void)
  30. {
  31. 	remove_proc_entry("fb", NULL);
  32. 	class_destroy(fb_class);
  33. 	unregister_chrdev(FB_MAJOR, "fb");
  34. }
  35.  
  36. module_exit(fbmem_exit);
  37. MODULE_LICENSE("GPL");
  38. MODULE_DESCRIPTION("Framebuffer base");
  39. #else
  40. subsys_initcall(fbmem_init);
  41. #endif
  42.  
  43. static const struct file_operations fb_fops = {
  44.     .owner =    THIS_MODULE,
  45.     .read =        fb_read,
  46.     .write =    fb_write,
  47.     .unlocked_ioctl = fb_ioctl,
  48. #ifdef CONFIG_COMPAT
  49.     .compat_ioctl = fb_compat_ioctl,
  50. #endif
  51.     .mmap =        fb_mmap,
  52.     .open =        fb_open,
  53.     .release =    fb_release,
  54. #ifdef HAVE_ARCH_FB_UNMAPPED_AREA
  55.     .get_unmapped_area = get_fb_unmapped_area,
  56. #endif
  57. #ifdef CONFIG_FB_DEFERRED_IO
  58.     .fsync =    fb_deferred_io_fsync,
  59. #endif
  60. };

我们看到，如果不是作为模块，那么该初始化程序将在subsys_initcall阶段被调用。初始化时，仅仅注册了一个字符设备，并创建了一个类。通过字符设备，提供了API给用户空间，包open，release，write，read等。

随后我们看看如何分配一个fb_info结构。

3.2 framebuffer_alloc

下列代码位于drivers/video/fbmem.c

  1. /**
  2.  * framebuffer_alloc - creates a new frame buffer info structure
  3.  *
  4.  * @size: size of driver private data, can be zero
  5.  * @dev: pointer to the device for this fb, this can be NULL
  6.  *
  7.  * Creates a new frame buffer info structure. Also reserves @size bytes
  8.  * for driver private data (info->par). info->par (if any) will be
  9.  * aligned to sizeof(long).
  10.  *
  11.  * Returns the new structure, or NULL if an error occured.
  12.  *
  13.  */
  14. struct fb_info *framebuffer_alloc(size_t size, struct device *dev)
  15. {
  16. #define BYTES_PER_LONG (BITS_PER_LONG/8)
  17. #define PADDING (BYTES_PER_LONG - (sizeof(struct fb_info) % BYTES_PER_LONG))
  18. 	int fb_info_size = sizeof(struct fb_info);
  19. 	struct fb_info *info;
  20. 	char *p;
  21.  
  22. 	if (size)
  23. 		fb_info_size += PADDING;
  24.  
  25. 	p = kzalloc(fb_info_size + size, GFP_KERNEL);
  26.  
  27. 	if (!p)
  28. 		return NULL;
  29.  
  30. 	info = (struct fb_info *) p;
  31.  
  32. 	if (size)
  33. 		info->par = p + fb_info_size;
  34.  
  35. 	info->device = dev;
  36.  
  37. #ifdef CONFIG_FB_BACKLIGHT
  38. 	mutex_init(&info->bl_curve_mutex);
  39. #endif
  40.  
  41. 	return info;
  42. #undef PADDING
  43. #undef BYTES_PER_LONG
  44. }
  45. EXPORT_SYMBOL(framebuffer_alloc);
在进行分配时，根据参数size的大小，分配了b_info_size + size的空间，然后让fb_info->par指向size的空间。因此par所指向的空间可视为设备特有的数据。

在分配了fb_info结构之后，需要将它注册到内核中。注册由register_framebuffer完成。我们来看下。

3.3 register_framebuffer

下列代码位于drivers/video/fbmem.c

  1. /**
  2.  *	register_framebuffer - registers a frame buffer device
  3.  *	@fb_info: frame buffer info structure
  4.  *
  5.  *	Registers a frame buffer device @fb_info.
  6.  *
  7.  *	Returns negative errno on error, or zero for success.
  8.  *
  9.  */
  10.  
  11. int
  12. register_framebuffer(struct fb_info *fb_info)
  13. {
  14. 	int i;
  15. 	struct fb_event event;
  16. 	struct fb_videomode mode;
  17.  
  18. 	if (num_registered_fb == FB_MAX) /*最多32个FB*/
  19. 		return -ENXIO;
  20.  
  21. 	if (fb_check_foreignness(fb_info))
  22. 		return -ENOSYS;
  23.  
  24. 	num_registered_fb++;		/*对注册的FB计数*/
  25. 	/*寻找第一个空位*/
  26. 	for (i = 0 ; i < FB_MAX; i++)/*FB_MAX=32,也就是最多32个framebuffer*/
  27. 		if (!registered_fb[i])	/*struct fb_info *registered_fb[FB_MAX]*/
  28. 			break;
  29. 	fb_info->node = i;
  30. 	mutex_init(&fb_info->lock);	/*初始化互斥体*/
  31.  
  32. 	fb_info->dev = device_create(fb_class, fb_info->device,/*创建设备节点，节点名为fbx*/
  33. 				     MKDEV(FB_MAJOR, i), NULL, "fb%d", i);
  34. 	if (IS_ERR(fb_info->dev)) {
  35. 		/* Not fatal */
  36. 		printk(KERN_WARNING "Unable to create device for framebuffer %d; errno = %ld\n", i, PTR_ERR(fb_info->dev));
  37. 		fb_info->dev = NULL;
  38. 	} else
  39. 		fb_init_device(fb_info);	/*初始化,在class/graphics/fbx/下创建设备属性*/
  40.  
  41. 	if (fb_info->pixmap.addr == NULL) {
  42. 		fb_info->pixmap.addr = kmalloc(FBPIXMAPSIZE, GFP_KERNEL);/*分配内存，1024 * 8字节*/
  43. 		if (fb_info->pixmap.addr) {
  44. 			fb_info->pixmap.size = FBPIXMAPSIZE;
  45. 			fb_info->pixmap.buf_align = 1;
  46. 			fb_info->pixmap.scan_align = 1;
  47. 			fb_info->pixmap.access_align = 32;
  48. 			fb_info->pixmap.flags = FB_PIXMAP_DEFAULT;
  49. 		}
  50. 	}	
  51. 	fb_info->pixmap.offset = 0;
  52.  
  53. 	if (!fb_info->pixmap.blit_x)
  54. 		fb_info->pixmap.blit_x = ~(u32)0;
  55.  
  56. 	if (!fb_info->pixmap.blit_y)
  57. 		fb_info->pixmap.blit_y = ~(u32)0;
  58.  
  59. 	if (!fb_info->modelist.prev || !fb_info->modelist.next)	/*该链表没有指向其他节点*/
  60. 		INIT_LIST_HEAD(&fb_info->modelist);	/*初始化链表头*/
  61.  
  62. 	fb_var_to_videomode(&mode, &fb_info->var);/*转换fb_var_screeninfo成fb_videomode*/
  63. 	fb_add_videomode(&mode, &fb_info->modelist);/*添加mode至链表中*/
  64. 	registered_fb[i] = fb_info;
  65.  
  66. 	event.info = fb_info;
  67. 	if (!lock_fb_info(fb_info))
  68. 		return -ENODEV;
  69. 	fb_notifier_call_chain(FB_EVENT_FB_REGISTERED, &event);/*???*/
  70. 	unlock_fb_info(fb_info);
  71. 	return 0;
  72. }

从这个函数我们可以看出，framebuffer子系统只支持32个设备。在创建了设备节点以后，建立设备属性节点，随后将fb_var_screeninfo转换成fb_videomode，最后添加fb_videomode至链表中。

我们看下其中调用的函数，首先是fb_init_device。

下列代码位于drivers/video/fbsysfs.c

  1. int fb_init_device(struct fb_info *fb_info)
  2. {
  3. 	int i, error = 0;
  4.  
  5. 	dev_set_drvdata(fb_info->dev, fb_info);
  6.  
  7. 	fb_info->class_flag |= FB_SYSFS_FLAG_ATTR;
  8.  
  9. 	/*建立设备属性*/
  10. 	for (i = 0; i < ARRAY_SIZE(device_attrs); i++) {
  11. 		error = device_create_file(fb_info->dev, &device_attrs[i]);
  12.  
  13. 		if (error)
  14. 			break;
  15. 	}
  16.  
  17. 	if (error) {
  18. 		while (--i >= 0)
  19. 			device_remove_file(fb_info->dev, &device_attrs[i]);
  20. 		fb_info->class_flag &= ~FB_SYSFS_FLAG_ATTR;
  21. 	}
  22.  
  23. 	return 0;
  24. }
  25.  
  26. /* When cmap is added back in it should be a binary attribute
  27.  * not a text one. Consideration should also be given to converting
  28.  * fbdev to use configfs instead of sysfs */
  29. static struct device_attribute device_attrs[] = {
  30.     __ATTR(bits_per_pixel, S_IRUGO|S_IWUSR, show_bpp, store_bpp),
  31.     __ATTR(blank, S_IRUGO|S_IWUSR, show_blank, store_blank),
  32.     __ATTR(console, S_IRUGO|S_IWUSR, show_console, store_console),
  33.     __ATTR(cursor, S_IRUGO|S_IWUSR, show_cursor, store_cursor),
  34.     __ATTR(mode, S_IRUGO|S_IWUSR, show_mode, store_mode),
  35.     __ATTR(modes, S_IRUGO|S_IWUSR, show_modes, store_modes),
  36.     __ATTR(pan, S_IRUGO|S_IWUSR, show_pan, store_pan),
  37.     __ATTR(virtual_size, S_IRUGO|S_IWUSR, show_virtual, store_virtual),
  38.     __ATTR(name, S_IRUGO, show_name, NULL),
  39.     __ATTR(stride, S_IRUGO, show_stride, NULL),
  40.     __ATTR(rotate, S_IRUGO|S_IWUSR, show_rotate, store_rotate),
  41.     __ATTR(state, S_IRUGO|S_IWUSR, show_fbstate, store_fbstate),
  42. #ifdef CONFIG_FB_BACKLIGHT
  43.     __ATTR(bl_curve, S_IRUGO|S_IWUSR, show_bl_curve, store_bl_curve),
  44. #endif
  45. };

我们可以在/sys/class/graphics/fb0下发现这些属性文件。

[root@yj423 fb0]#pwd
/sys/class/graphics/fb0
[root@yj423 fb0]#ls
bits_per_pixel  cursor          mode            pan             state           uevent
blank           dev             modes           power           stride          virtual_size
console         device          name            rotate          subsystem


接着看下fb_var_to_videomode和fb_add_videomode函数。

下列代码位于drivers/video/modedb.c和drivers/video/fb.h

  1. struct fb_videomode {
  2. 	const char *name;	/* optional */
  3. 	u32 refresh;		/* optional */
  4. 	u32 xres;
  5. 	u32 yres;
  6. 	u32 pixclock;
  7. 	u32 left_margin;
  8. 	u32 right_margin;
  9. 	u32 upper_margin;
  10. 	u32 lower_margin;
  11. 	u32 hsync_len;
  12. 	u32 vsync_len;
  13. 	u32 sync;
  14. 	u32 vmode;
  15. 	u32 flag;
  16. };
  17.  
  18. /**
  19.  * fb_var_to_videomode - convert fb_var_screeninfo to fb_videomode
  20.  * @mode: pointer to struct fb_videomode
  21.  * @var: pointer to struct fb_var_screeninfo
  22.  */
  23. void fb_var_to_videomode(struct fb_videomode *mode,
  24.              const struct fb_var_screeninfo *var)
  25. {
  26.     u32 pixclock, hfreq, htotal, vtotal;
  27.  
  28.     mode->name = NULL;
  29.     mode->xres = var->xres;
  30.     mode->yres = var->yres;
  31.     mode->pixclock = var->pixclock;
  32.     mode->hsync_len = var->hsync_len;
  33.     mode->vsync_len = var->vsync_len;
  34.     mode->left_margin = var->left_margin;
  35.     mode->right_margin = var->right_margin;
  36.     mode->upper_margin = var->upper_margin;
  37.     mode->lower_margin = var->lower_margin;
  38.     mode->sync = var->sync;
  39.     mode->vmode = var->vmode & FB_VMODE_MASK;
  40.     mode->flag = FB_MODE_IS_FROM_VAR;
  41.     mode->refresh = 0;
  42.  
  43.     if (!var->pixclock)
  44.         return;
  45.  
  46.     pixclock = PICOS2KHZ(var->pixclock) * 1000;
  47.  
  48.     htotal = var->xres + var->right_margin + var->hsync_len +
  49.         var->left_margin;
  50.     vtotal = var->yres + var->lower_margin + var->vsync_len +
  51.         var->upper_margin;
  52.  
  53.     if (var->vmode & FB_VMODE_INTERLACED)
  54.         vtotal /= 2;
  55.     if (var->vmode & FB_VMODE_DOUBLE)
  56.         vtotal *= 2;
  57.  
  58.     hfreq = pixclock/htotal;
  59.     mode->refresh = hfreq/vtotal;
  60. }
  61.  
  62. /**
  63.  * fb_add_videomode: adds videomode entry to modelist
  64.  * @mode: videomode to add
  65.  * @head: struct list_head of modelist
  66.  *
  67.  * NOTES:
  68.  * Will only add unmatched mode entries
  69.  */
  70. int fb_add_videomode(const struct fb_videomode *mode, struct list_head *head)
  71. {
  72.     struct list_head *pos;
  73.     struct fb_modelist *modelist;d
  74.     struct fb_videomode *m;
  75.     int found = 0;
  76.     /*遍历所有的fb_modelist，查找mode是否存在*/
  77.     list_for_each(pos, head) {
  78.         modelist = list_entry(pos, struct fb_modelist, list);
  79.         m = &modelist->mode;
  80.         if (fb_mode_is_equal(m, mode)) {    /*比较两个fb_videomode*/
  81.             found = 1;                        /*该fb_videomode已存在*/
  82.             break;
  83.         }
  84.     }
  85.     if (!found) {    /*不存在*/
  86.         modelist = kmalloc(sizeof(struct fb_modelist),    /*分配fb_modelist*/
  87.                           GFP_KERNEL);
  88.  
  89.         if (!modelist)
  90.             return -ENOMEM;
  91.         modelist->mode = *mode;            /*保存mode*/
  92.         list_add(&modelist->list, head);/*添加mode至链表中*/
  93.     }
  94.     return 0;
  95. }
  96.  
  97. /**
  98.  * fb_mode_is_equal - compare 2 videomodes
  99.  * @mode1: first videomode
  100.  * @mode2: second videomode
  101.  *
  102.  * RETURNS:
  103.  * 1 if equal, 0 if not
  104.  */
  105. int fb_mode_is_equal(const struct fb_videomode *mode1,
  106.              const struct fb_videomode *mode2)
  107. {
  108.     return (mode1->xres         == mode2->xres &&
  109.         mode1->yres         == mode2->yres &&
  110.         mode1->pixclock     == mode2->pixclock &&
  111.         mode1->hsync_len    == mode2->hsync_len &&
  112.         mode1->vsync_len    == mode2->vsync_len &&
  113.         mode1->left_margin  == mode2->left_margin &&
  114.         mode1->right_margin == mode2->right_margin &&
  115.         mode1->upper_margin == mode2->upper_margin &&
  116.         mode1->lower_margin == mode2->lower_margin &&
  117.         mode1->sync         == mode2->sync &&
  118.         mode1->vmode        == mode2->vmode);
  119. }
  120.

fb_var_to_videomode函数只是将fb_var_screeninfo结构转换成fb_videomode结构。而fb_add_videomode函数查找是否该fb_videomode已经存在，如果不存在则添加到列表中。

3.4 字符设备方法

  在看过framebuffer子系统建立和注册过程后，我们看下framebuffer留给用户空间的API是怎样实现的。

本小结只分析5个常用的方法，即open，release，read，write和ioctl。

  因为所有的方法和struct fb_ops定义的方法有紧密的联系，而该结构的定义由驱动程序给出，在这里我们提前看下在驱动中是如何定义的。

 下列代码位于drivers/video/s3c2410fb..c

  1. static struct fb_ops s3c2410fb_ops = {
  2. 	.owner		= THIS_MODULE,
  3. 	.fb_check_var	= s3c2410fb_check_var,		        /*检查变量的合法性*/
  4. 	.fb_set_par	= s3c2410fb_set_par,			/*将参数写入LCD控制器，该函数由帧缓冲核心调用*/
  5. 	.fb_blank	= s3c2410fb_blank,			/*该方法支持显示消隐和去消隐*/
  6. 	.fb_setcolreg	= s3c2410fb_setcolreg,                  /*设置颜色寄存器*/
  7. 	.fb_fillrect	= cfb_fillrect,				/*用像素行填充矩形框，通用库函数*/
  8. 	.fb_copyarea	= cfb_copyarea,				/*将屏幕的一个矩形区域复制到另一个区域，通用库函数*/
  9. 	.fb_imageblit	= cfb_imageblit,			/*显示一副图像，通用库函数*/
  10. };
最下面的三个方法使用的是内核提供的库函数，而上面4个则是由驱动提供。

3.4.1 open方法

下列代码位于drivers/video/fbmem.c

  1. static int
  2. fb_open(struct inode *inode, struct file *file)
  3. __acquires(&info->lock)
  4. __releases(&info->lock)
  5. {
  6. 	int fbidx = iminor(inode);
  7. 	struct fb_info *info;
  8. 	int res = 0;
  9.  
  10. 	if (fbidx >= FB_MAX)
  11. 		return -ENODEV;
  12. 	info = registered_fb[fbidx];		/*在register_framebuffer函数中已经设置了元素*/
  13. 	if (!info)
  14. 		request_module("fb%d", fbidx);	/*加载模块，这里不加载*/
  15. 	info = registered_fb[fbidx];
  16. 	if (!info)
  17. 		return -ENODEV;
  18. 	mutex_lock(&info->lock);			/*加锁互斥体*/
  19. 	if (!try_module_get(info->fbops->owner)) {	/*增加模块引用计数*/
  20. 		res = -ENODEV;
  21. 		goto out;
  22. 	}
  23. 	file->private_data = info;		/*保存info*/
  24. 	if (info->fbops->fb_open) {		/*这里fb_open方法为空*/
  25. 		res = info->fbops->fb_open(info,1);
  26. 		if (res)
  27. 			module_put(info->fbops->owner);
  28. 	}
  29. #ifdef CONFIG_FB_DEFERRED_IO
  30. 	if (info->fbdefio)
  31. 		fb_deferred_io_open(info, inode, file);
  32. #endif
  33. out:
  34. 	mutex_unlock(&info->lock);		/*解锁互斥体*/
  35. 	return res;
  36. }
主要的一个工作就是增加模块引用计数。还有，程序会判断是否fb_open在驱动中给出，如果有则调用该方法。我们已经知道fb_open没有给出。

3.4.2 release方法

下列代码位于drivers/video/fbmem.c

  1. static int 
  2. fb_release(struct inode *inode, struct file *file)
  3. __acquires(&info->lock)
  4. __releases(&info->lock)
  5. {
  6. 	struct fb_info * const info = file->private_data;
  7.  
  8. 	mutex_lock(&info->lock);
  9. 	if (info->fbops->fb_release)	/*这里fb_release为空*/
  10. 		info->fbops->fb_release(info,1);
  11. 	module_put(info->fbops->owner);	/*减少模块引用计数*/
  12. 	mutex_unlock(&info->lock);
  13. 	return 0;
  14. }

和open相反，减少模块引用计数。

3.4.3 write方法

  通过调用该方法，LCD将显示画面。

  下列代码位于drivers/video/fbmem.c

  1. static ssize_t
  2. fb_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
  3. {
  4.     unsigned long p = *ppos;
  5.     struct inode *inode = file->f_path.dentry->d_inode;
  6.     int fbidx = iminor(inode);
  7.     struct fb_info *info = registered_fb[fbidx];
  8.     u32 *buffer, *src;
  9.     u32 __iomem *dst;
  10.     int c, i, cnt = 0, err = 0;
  11.     unsigned long total_size;
  12.  
  13.     if (!info || !info->screen_base)    /*screen_base在驱动中给出*/
  14.         return -ENODEV;
  15.  
  16.     if (info->state != FBINFO_STATE_RUNNING)
  17.         return -EPERM;
  18.  
  19.     if (info->fbops->fb_write)    /*没有fb_write方法*/
  20.         return info->fbops->fb_write(info, buf, count, ppos);
  21.     
  22.     total_size = info->screen_size;    /*screen_size没有给出*/
  23.  
  24.     if (total_size == 0)
  25.         total_size = info->fix.smem_len;/*153600字节，驱动probe方法中计算*/
  26.  
  27.     if (p > total_size)
  28.         return -EFBIG;
  29.  
  30.     if (count > total_size) {    /*要写入的字节数大于153600*/
  31.         err = -EFBIG;        /*file too big*/
  32.         count = total_size;
  33.     }
  34.  
  35.     if (count + p > total_size) {/*偏移量加上字节数超出了缓冲区*/
  36.         if (!err)
  37.             err = -ENOSPC;
  38.  
  39.         count = total_size - p;
  40.     }
  41.  
  42.     /*分配buffer，GFP_KERNEL*/
  43.     buffer = kmalloc((count > PAGE_SIZE) ? PAGE_SIZE : count,
  44.              GFP_KERNEL);                /
  45.     if (!buffer)
  46.         return -ENOMEM;
  47.  
  48.     dst = (u32 __iomem *) (info->screen_base + p);/*修改目的指针*/
  49.  
  50.     if (info->fbops->fb_sync)    /*没有定义fb_sync*/
  51.         info->fbops->fb_sync(info);
  52.  
  53.     while (count) {
  54.         c = (count > PAGE_SIZE) ? PAGE_SIZE : count;
  55.         src = buffer;
  56.  
  57.         /*从buf(用户空间)拷贝数据到src中，一开始为1页，最后为count字节*/
  58.         if (copy_from_user(src, buf, c)) {    
  59.             err = -EFAULT;
  60.             break;
  61.         }
  62.         /*一次for循环，写入4个字节数据到dst处*/
  63.         for (i = c >> 2; i--; )
  64.             fb_writel(*src++, dst++);
  65.         /*最后还有3个，2个或者1个字节*/
  66.         if (c & 3) {
  67.             u8 *src8 = (u8 *) src;
  68.             u8 __iomem *dst8 = (u8 __iomem *) dst;
  69.             /*一次写入一个字节*/
  70.             for (i = c & 3; i--; )
  71.                 fb_writeb(*src8++, dst8++);
  72.  
  73.             dst = (u32 __iomem *) dst8;
  74.         }
  75.  
  76.         *ppos += c;    /*用户空间偏移量增加*/
  77.         buf += c;    /*用户空间指针增加*/
  78.         cnt += c;    /*修改已发送字节数*/
  79.         count -= c;    /*减去1页*/
  80.     }
  81.  
  82.     kfree(buffer);    /*释放buffer*/
  83.  
  84.     return (cnt) ? cnt : err;
  85. }

这里，做了一系列的检查之后，开始拷贝数据。这里一个有三个buffer，一个是用户空间提供的buf，一个是在这里新开辟的buffer，还有就是驱动层提供的screen_base。

数据流如下：
 

用户空间的数据首先被复制到buffer中，然后从buffer中复制到screen_base中，最后被映射到LCD上，LCD就显示响应的画面了。

3.4.4 read方法

该方法用于读取屏幕画面的数据。

read和write类似，只是数据流是反响的，就不多做介绍了。

下列代码位于drivers/video/fbmem.c

  1. static ssize_t
  2. fb_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
  3. {
  4. 	unsigned long p = *ppos;
  5. 	struct inode *inode = file->f_path.dentry->d_inode;
  6. 	int fbidx = iminor(inode);
  7. 	struct fb_info *info = registered_fb[fbidx];
  8. 	u32 *buffer, *dst;
  9. 	u32 __iomem *src;
  10. 	int c, i, cnt = 0, err = 0;
  11. 	unsigned long total_size;
  12.  
  13. 	if (!info || ! info->screen_base)
  14. 		return -ENODEV;
  15.  
  16. 	if (info->state != FBINFO_STATE_RUNNING)
  17. 		return -EPERM;
  18.  
  19. 	if (info->fbops->fb_read)	/*没有定义fb_read*/
  20. 		return info->fbops->fb_read(info, buf, count, ppos);
  21. 	
  22. 	total_size = info->screen_size;
  23.  
  24. 	if (total_size == 0)
  25. 		total_size = info->fix.smem_len;
  26.  
  27. 	if (p >= total_size)
  28. 		return 0;
  29.  
  30. 	if (count >= total_size)
  31. 		count = total_size;
  32.  
  33. 	if (count + p > total_size)
  34. 		count = total_size - p;
  35.  
  36. 	buffer = kmalloc((count > PAGE_SIZE) ? PAGE_SIZE : count,
  37. 			 GFP_KERNEL);
  38. 	if (!buffer)
  39. 		return -ENOMEM;
  40.  
  41. 	src = (u32 __iomem *) (info->screen_base + p);
  42.  
  43. 	if (info->fbops->fb_sync)
  44. 		info->fbops->fb_sync(info);/*没有定义fb_sync*/
  45.  
  46. 	while (count) {
  47. 		c  = (count > PAGE_SIZE) ? PAGE_SIZE : count;
  48. 		dst = buffer;
  49. 		for (i = c >> 2; i--; )
  50. 			*dst++ = fb_readl(src++);
  51. 		if (c & 3) {
  52. 			u8 *dst8 = (u8 *) dst;
  53. 			u8 __iomem *src8 = (u8 __iomem *) src;
  54.  
  55. 			for (i = c & 3; i--;)
  56. 				*dst8++ = fb_readb(src8++);
  57.  
  58. 			src = (u32 __iomem *) src8;
  59. 		}
  60.  
  61. 		if (copy_to_user(buf, buffer, c)) {
  62. 			err = -EFAULT;
  63. 			break;
  64. 		}
  65. 		*ppos += c;
  66. 		buf += c;
  67. 		cnt += c;
  68. 		count -= c;
  69. 	}
  70.  
  71. 	kfree(buffer);
  72.  
  73. 	return (err) ? err : cnt;
  74. }
3.4.5 ioctl方法

这里只是简单的看下ioctl方法，这个函数调用很多其他的函数，详细的请自己看吧。

下列代码位于drivers/video/fbmem.c

  1. static long fb_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
  2. {
  3. 	/*获取inode，再获取对应的fb_info*/
  4. 	struct inode *inode = file->f_path.dentry->d_inode;
  5. 	int fbidx = iminor(inode);	
  6. 	struct fb_info *info = registered_fb[fbidx];
  7.  
  8. 	return do_fb_ioctl(info, cmd, arg);
  9. }
  10.  
  11. static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
  12.             unsigned long arg)
  13. {
  14.     struct fb_ops *fb;
  15.     struct fb_var_screeninfo var;
  16.     struct fb_fix_screeninfo fix;
  17.     struct fb_con2fbmap con2fb;
  18.     struct fb_cmap cmap_from;
  19.     struct fb_cmap_user cmap;
  20.     struct fb_event event;
  21.     void __user *argp = (void __user *)arg;
  22.     long ret = 0;
  23.  
  24.     switch (cmd) {
  25.     /*获取fb_var_screeninfo*/
  26.     case FBIOGET_VSCREENINFO:    
  27.         if (!lock_fb_info(info))    /*加锁互斥体info->lock*/
  28.             return -ENODEV;
  29.         var = info->var;            /*复制var*/
  30.         unlock_fb_info(info);
  31.  
  32.         ret = copy_to_user(argp, &var, sizeof(var)) ? -EFAULT : 0;    /*复制var到用户空间*/
  33.         break;
  34.     /*设置fb_var_screeninfo*/
  35.     case FBIOPUT_VSCREENINFO:
  36.         if (copy_from_user(&var, argp, sizeof(var)))    /*从用户空间获取var*/
  37.             return -EFAULT;
  38.         if (!lock_fb_info(info))
  39.             return -ENODEV;
  40.         acquire_console_sem();
  41.         info->flags |= FBINFO_MISC_USEREVENT;
  42.         ret = fb_set_var(info, &var);            /*设置var*/
  43.         info->flags &= ~FBINFO_MISC_USEREVENT;
  44.         release_console_sem();
  45.         unlock_fb_info(info);
  46.         if (!ret && copy_to_user(argp, &var, sizeof(var)))
  47.             ret = -EFAULT;
  48.         break;
  49.     /*获取fb_fix_screeninfo*/    /*fix为不可改变信息，只能获取，不能设置*/
  50.     case FBIOGET_FSCREENINFO:
  51.         if (!lock_fb_info(info))
  52.             return -ENODEV;
  53.         fix = info->fix;
  54.         unlock_fb_info(info);
  55.  
  56.         ret = copy_to_user(argp, &fix, sizeof(fix)) ? -EFAULT : 0;
  57.         break;
  58.     /*设置fb_cmap*/    
  59.     case FBIOPUTCMAP:
  60.         if (copy_from_user(&cmap, argp, sizeof(cmap)))
  61.             return -EFAULT;
  62.         ret = fb_set_user_cmap(&cmap, info);    /*设置fb_cmap*/
  63.         break;
  64.     /*获取fb_cmap*/    
  65.     case FBIOGETCMAP:
  66.         if (copy_from_user(&cmap, argp, sizeof(cmap)))
  67.             return -EFAULT;
  68.         if (!lock_fb_info(info))
  69.             return -ENODEV;
  70.         cmap_from = info->cmap;
  71.         unlock_fb_info(info);
  72.         ret = fb_cmap_to_user(&cmap_from, &cmap);/*获取fb_cmp*/
  73.         break;
  74.     case FBIOPAN_DISPLAY:
  75.         if (copy_from_user(&var, argp, sizeof(var)))
  76.             return -EFAULT;
  77.         if (!lock_fb_info(info))
  78.             return -ENODEV;
  79.         acquire_console_sem();
  80.         ret = fb_pan_display(info, &var);
  81.         release_console_sem();
  82.         unlock_fb_info(info);
  83.         if (ret == 0 && copy_to_user(argp, &var, sizeof(var)))
  84.             return -EFAULT;
  85.         break;
  86.     case FBIO_CURSOR:
  87.         ret = -EINVAL;
  88.         break;
  89.     case FBIOGET_CON2FBMAP:
  90.         if (copy_from_user(&con2fb, argp, sizeof(con2fb)))
  91.             return -EFAULT;
  92.         if (con2fb.console < 1 || con2fb.console > MAX_NR_CONSOLES)
  93.             return -EINVAL;
  94.         con2fb.framebuffer = -1;
  95.         event.data = &con2fb;
  96.         if (!lock_fb_info(info))
  97.             return -ENODEV;
  98.         event.info = info;
  99.         fb_notifier_call_chain(FB_EVENT_GET_CONSOLE_MAP, &event);
  100.         unlock_fb_info(info);
  101.         ret = copy_to_user(argp, &con2fb, sizeof(con2fb)) ? -EFAULT : 0;
  102.         break;
  103.     case FBIOPUT_CON2FBMAP:
  104.         if (copy_from_user(&con2fb, argp, sizeof(con2fb)))
  105.             return -EFAULT;
  106.         if (con2fb.console < 1 || con2fb.console > MAX_NR_CONSOLES)
  107.             return -EINVAL;
  108.         if (con2fb.framebuffer < 0 || con2fb.framebuffer >= FB_MAX)
  109.             return -EINVAL;
  110.         if (!registered_fb[con2fb.framebuffer])
  111.             request_module("fb%d", con2fb.framebuffer);
  112.         if (!registered_fb[con2fb.framebuffer]) {
  113.             ret = -EINVAL;
  114.             break;
  115.         }
  116.         event.data = &con2fb;
  117.         if (!lock_fb_info(info))
  118.             return -ENODEV;
  119.         event.info = info;
  120.         ret = fb_notifier_call_chain(FB_EVENT_SET_CONSOLE_MAP, &event);
  121.         unlock_fb_info(info);
  122.         break;
  123.     case FBIOBLANK:
  124.         if (!lock_fb_info(info))
  125.             return -ENODEV;
  126.         acquire_console_sem();
  127.         info->flags |= FBINFO_MISC_USEREVENT;
  128.         ret = fb_blank(info, arg);        ?*最后调用驱动提供的s3c2410fb_blank*/
  129.         info->flags &= ~FBINFO_MISC_USEREVENT;
  130.         release_console_sem();
  131.         unlock_fb_info(info);
  132.         break;
  133.     default:
  134.         if (!lock_fb_info(info))
  135.             return -ENODEV;
  136.         fb = info->fbops;
  137.         if (fb->fb_ioctl)        /*fb_ioctl为空*/
  138.             ret = fb->fb_ioctl(info, cmd, arg);
  139.         else
  140.             ret = -ENOTTY;
  141.         unlock_fb_info(info);
  142.     }
  143.     return ret;
  144. }

正如2.2小结所说的，fb_fix_screeninfo只能获取不能设置，因此，ioctl只提供了获取fb_fix_screeninfo的方法，而没有提供设置fb_fix_screeninfo的方法。

3.5 小结

  本节对frambuffer的核心层进行了介绍。包括frambuffer子系统的创建，frambuffer的注册和提供给用户空间的5个API函数。下面开始介绍驱动层。

4. 驱动层

本节将开始介绍S3C2440的frambuffer驱动，该驱动源码位于drivers/video/s3c2410fb.c

首先来看下驱动模块的初始化和清除函数。

4.1 s3c2410fb_init和s3c2410fb_cleanup

  1. static struct platform_driver s3c2410fb_driver = {
  2.     .probe        = s3c2410fb_probe,
  3.     .remove        = s3c2410fb_remove,
  4.     .suspend    = s3c2410fb_suspend,
  5.     .resume        = s3c2410fb_resume,
  6.     .driver        = {
  7.         .name    = "s3c2410-lcd",
  8.         .owner    = THIS_MODULE,
  9.     },
  10. };
  11.  
  12. int __init s3c2410fb_init(void)
  13. {
  14. 	int ret = platform_driver_register(&s3c2410fb_driver);
  15.  
  16. 	if (ret == 0)
  17. 		ret = platform_driver_register(&s3c2412fb_driver);;
  18.  
  19. 	return ret;
  20. }
  21.  
  22. static void __exit s3c2410fb_cleanup(void)
  23. {
  24. 	platform_driver_unregister(&s3c2410fb_driver);
  25. 	platform_driver_unregister(&s3c2412fb_driver);
  26. }
  27.  
  28. module_init(s3c2410fb_init);
  29. module_exit(s3c2410fb_cleanup);

当platform_driver_register调用的最后会调用probe方法。接下来就来看看probe方法。

4.2 probe方法

  1. struct s3c2410fb_info {
  2.     struct device        *dev;
  3.     struct clk        *clk;
  4.  
  5.     struct resource        *mem;
  6.     void __iomem        *io;        /*虚拟地址*/
  7.     void __iomem        *irq_base;
  8.  
  9.     enum s3c_drv_type    drv_type;
  10.     struct s3c2410fb_hw    regs;
  11.  
  12.     unsigned int        palette_ready;
  13.  
  14.     /* keep these registers in case we need to re-write palette */
  15.     u32            palette_buffer[256];
  16.     u32            pseudo_pal[16];
  17. };
  18.  
  19. struct s3c2410fb_mach_info {
  20.  
  21. 	struct s3c2410fb_display *displays;	/* attached diplays info */
  22. 	unsigned num_displays;			/* number of defined displays */
  23. 	unsigned default_display;
  24.  
  25. 	/* GPIOs */
  26.  
  27. 	unsigned long	gpcup;
  28. 	unsigned long	gpcup_mask;
  29. 	unsigned long	gpccon;
  30. 	unsigned long	gpccon_mask;
  31. 	unsigned long	gpdup;
  32. 	unsigned long	gpdup_mask;
  33. 	unsigned long	gpdcon;
  34. 	unsigned long	gpdcon_mask;
  35.  
  36. 	/* lpc3600 control register */
  37. 	unsigned long	lpcsel;
  38. };
  39.  
  40. /* LCD description */
  41. struct s3c2410fb_display {
  42.     /* LCD type */
  43.     unsigned type;
  44.  
  45.     /* Screen size */
  46.     unsigned short width;
  47.     unsigned short height;
  48.  
  49.     /* Screen info */
  50.     unsigned short xres;
  51.     unsigned short yres;
  52.     unsigned short bpp;
  53.  
  54.     unsigned pixclock;        /* pixclock in picoseconds */
  55.     unsigned short left_margin;  /* value in pixels (TFT) or HCLKs (STN) */
  56.     unsigned short right_margin; /* value in pixels (TFT) or HCLKs (STN) */
  57.     unsigned short hsync_len;    /* value in pixels (TFT) or HCLKs (STN) */
  58.     unsigned short upper_margin;    /* value in lines (TFT) or 0 (STN) */
  59.     unsigned short lower_margin;    /* value in lines (TFT) or 0 (STN) */
  60.     unsigned short vsync_len;    /* value in lines (TFT) or 0 (STN) */
  61.  
  62.     /* lcd configuration registers */
  63.     unsigned long    lcdcon5;
  64. };
  65.  
  66. static int __init s3c24xxfb_probe(struct platform_device *pdev,
  67.                   enum s3c_drv_type drv_type)
  68. {
  69.     struct s3c2410fb_info *info;
  70.     struct s3c2410fb_display *display;
  71.     struct fb_info *fbinfo;
  72.     struct s3c2410fb_mach_info *mach_info;
  73.     struct resource *res;
  74.     int ret;
  75.     int irq;
  76.     int i;
  77.     int size;
  78.     u32 lcdcon1;
  79.     /*dev.platform_data由函数s3c24xx_fb_set_platdata(mach-smdk2410.c)设置，指向s3c2410fb_mach_info*/
  80.     mach_info = pdev->dev.platform_data;    
  81.     if (mach_info == NULL) {
  82.         dev_err(&pdev->dev,
  83.             "no platform data for lcd, cannot attach\n");
  84.         return -EINVAL;
  85.     }
  86.                                     /*在mach-smdk2440.c中，default_display=0, num_displays=1*/
  87.     if (mach_info->default_display >= mach_info->num_displays) {     
  88.         dev_err(&pdev->dev, "default is %d but only %d displays\n",
  89.             mach_info->default_display, mach_info->num_displays);
  90.         return -EINVAL;
  91.     }
  92.  
  93.     display = mach_info->displays + mach_info->default_display;
  94.  
  95.     irq = platform_get_irq(pdev, 0);    /*获取IRQ号,16号中断*/
  96.     if (irq < 0) {
  97.         dev_err(&pdev->dev, "no irq for device\n");
  98.         return -ENOENT;
  99.     }
  100.                                         /*分配struct fb_info 其中包括sizeof字节的私有数据区*/
  101.     fbinfo = framebuffer_alloc(sizeof(struct s3c2410fb_info), &pdev->dev);
  102.     if (!fbinfo)
  103.         return -ENOMEM;
  104.  
  105.     platform_set_drvdata(pdev, fbinfo);    /*让platform_device->dev.driver_data指向struct fb_info*/
  106.  
  107.     info = fbinfo->par;                    /*par指向s3c2410fb_info*/
  108.     info->dev = &pdev->dev;
  109.     info->drv_type = drv_type;
  110.  
  111.     res = platform_get_resource(pdev, IORESOURCE_MEM, 0);/*获取平台资源*/
  112.     if (res == NULL) {
  113.         dev_err(&pdev->dev, "failed to get memory registers\n");
  114.         ret = -ENXIO;
  115.         goto dealloc_fb;
  116.     }
  117.  
  118.     size = (res->end - res->start) + 1;                /*IO内存申请*/
  119.     info->mem = request_mem_region(res->start, size, pdev->name);    
  120.     if (info->mem == NULL) {
  121.         dev_err(&pdev->dev, "failed to get memory region\n");
  122.         ret = -ENOENT;
  123.         goto dealloc_fb;
  124.     }
  125.  
  126.     info->io = ioremap(res->start, size);            /*IO内存映射,获取lcd第一个寄存器的映射地址*/                
  127.     if (info->io == NULL) {
  128.         dev_err(&pdev->dev, "ioremap() of registers failed\n");        
  129.         ret = -ENXIO;    
  130.         goto release_mem;
  131.     }
  132.                                             /*irq_base对应的物理地址是0X4D00 0054(寄存器LCDINTPND)*/
  133.     info->irq_base = info->io + ((drv_type == DRV_S3C2412) ? S3C2412_LCDINTBASE : S3C2410_LCDINTBASE);
  134.                                                                             
  135.     dprintk("devinit\n");
  136.  
  137.     strcpy(fbinfo->fix.id, driver_name);    /*复制名字*/
  138.  
  139.     /* Stop the video */
  140.     lcdcon1 = readl(info->io + S3C2410_LCDCON1);
  141.     writel(lcdcon1 & ~S3C2410_LCDCON1_ENVID, info->io + S3C2410_LCDCON1); /*禁止LCD*/
  142.  
  143.     fbinfo->fix.type        = FB_TYPE_PACKED_PIXELS;
  144.     fbinfo->fix.type_aux        = 0;
  145.     fbinfo->fix.xpanstep        = 0;
  146.     fbinfo->fix.ypanstep        = 0;
  147.     fbinfo->fix.ywrapstep        = 0;
  148.     fbinfo->fix.accel        = FB_ACCEL_NONE;    /* no hardware accelerator    */
  149.  
  150.     fbinfo->var.nonstd        = 0;
  151.     fbinfo->var.activate        = FB_ACTIVATE_NOW;
  152.     fbinfo->var.accel_flags     = 0;
  153.     fbinfo->var.vmode        = FB_VMODE_NONINTERLACED;
  154.  
  155.     fbinfo->fbops            = &s3c2410fb_ops;
  156.     fbinfo->flags            = FBINFO_FLAG_DEFAULT;
  157.     fbinfo->pseudo_palette      = &info->pseudo_pal;
  158.  
  159.     for (i = 0; i < 256; i++)
  160.         info->palette_buffer[i] = PALETTE_BUFF_CLEAR;
  161.  
  162.     ret = request_irq(irq, s3c2410fb_irq, IRQF_DISABLED, pdev->name, info);    /*申请IRQ，快速中断*/
  163.     if (ret) {
  164.         dev_err(&pdev->dev, "cannot get irq %d - err %d\n", irq, ret);
  165.         ret = -EBUSY;
  166.         goto release_regs;
  167.     }
  168.  
  169.     info->clk = clk_get(NULL, "lcd");        /*获取时钟信息*/
  170.     if (!info->clk || IS_ERR(info->clk)) {
  171.         printk(KERN_ERR "failed to get lcd clock source\n");
  172.         ret = -ENOENT;
  173.         goto release_irq;
  174.     }
  175.  
  176.     clk_enable(info->clk);                    /*使能时钟*/
  177.     dprintk("got and enabled clock\n");
  178.  
  179.     msleep(1);
  180.  
  181.     /* find maximum required memory size for display */
  182.     /*在多个屏幕中，找出需要的最大memory*/
  183.     for (i = 0; i < mach_info->num_displays; i++) {
  184.         unsigned long smem_len = mach_info->displays[i].xres;
  185.         /*所需的memory空间 = xres * yres * bpp / 8*/
  186.         smem_len *= mach_info->displays[i].yres;
  187.         smem_len *= mach_info->displays[i].bpp;
  188.         smem_len >>= 3;
  189.         if (fbinfo->fix.smem_len < smem_len)
  190.             fbinfo->fix.smem_len = smem_len;
  191.     }
  192.  
  193.     /* Initialize video memory */    /*根据上面fix.smem_len的大小，获取DMA映射内存，一致性映射方式*/
  194.     ret = s3c2410fb_map_video_memory(fbinfo);
  195.     if (ret) {
  196.         printk(KERN_ERR "Failed to allocate video RAM: %d\n", ret);
  197.         ret = -ENOMEM;
  198.         goto release_clock;
  199.     }
  200.  
  201.     dprintk("got video memory\n");
  202.  
  203.     fbinfo->var.xres = display->xres;            /*320*/
  204.     fbinfo->var.yres = display->yres;            /*240*/    
  205.     fbinfo->var.bits_per_pixel = display->bpp;    /*16*/
  206.  
  207.     s3c2410fb_init_registers(fbinfo);            /*LCD寄存器初始化*/        
  208.  
  209.     s3c2410fb_check_var(&fbinfo->var, fbinfo);
  210.  
  211.     ret = register_framebuffer(fbinfo);            /*注册framebuffer*/
  212.     if (ret < 0) {
  213.         printk(KERN_ERR "Failed to register framebuffer device: %d\n",ret);
  214.         goto free_video_memory;
  215.     }
  216.  
  217.     /* create device files */
  218.     ret = device_create_file(&pdev->dev, &dev_attr_debug); /*添加设备属性*/
  219.     if (ret) {
  220.         printk(KERN_ERR "failed to add debug attribute\n");
  221.     }
  222.  
  223.     printk(KERN_INFO "fb%d: %s frame buffer device\n",
  224.         fbinfo->node, fbinfo->fix.id);
  225.  
  226.     return 0;
  227. /*一旦某个步骤发生错误，以注册的相反顺序开始注销*/
  228. free_video_memory:
  229.     s3c2410fb_unmap_video_memory(fbinfo);
  230. release_clock:
  231.     clk_disable(info->clk);
  232.     clk_put(info->clk);
  233. release_irq:
  234.     free_irq(irq, info);
  235. release_regs:
  236.     iounmap(info->io);
  237. release_mem:
  238.     release_resource(info->mem);
  239.     kfree(info->mem);
  240. dealloc_fb:
  241.     platform_set_drvdata(pdev, NULL);
  242.     framebuffer_release(fbinfo);    
  243.     return ret;
  244. }

这里使用了三个新的数据结构。s3c2410fb_info是驱动程序使用的，里面将保存所有驱动程序所要使用的资源等。而s3c2410fb_display和s3c2410fb_mach_info，是由板级信息，通过platform总线添加到内核中。

s3c2410fb_display中的成员将被复制到fb_var_screeninfo结构中。

该板级信息的定义在arch/arm/mach-s3c2440/mach-smdk2440.c中,来看下

  1. static struct s3c2410fb_display smdk2440_lcd_cfg __initdata = {
  2.  
  3. 	.lcdcon5	= S3C2410_LCDCON5_FRM565 |
  4. 			  S3C2410_LCDCON5_INVVLINE |
  5. 			  S3C2410_LCDCON5_INVVFRAME |
  6. 			  S3C2410_LCDCON5_PWREN |
  7. 			  S3C2410_LCDCON5_HWSWP,
  8.  
  9. 	.type		= S3C2410_LCDCON1_TFT,
  10.  
  11. 	.width		= 320,//240,
  12. 	.height		= 240,//320,
  13.  
  14. 	.pixclock	= 149000,//166667, /* HCLK 60 MHz, divisor 10 */
  15. 	.xres		= 320,//240,
  16. 	.yres		= 240,//320,
  17. 	.bpp		= 16,
  18. 	.left_margin	= 20,
  19. 	.right_margin	= 38,//8,
  20. 	.hsync_len	= 30,//4,
  21. 	.upper_margin	= 15,//8,
  22. 	.lower_margin	= 12,//7,
  23. 	.vsync_len	= 3,//4,
  24. };
  25.  
  26. static struct s3c2410fb_mach_info smdk2440_fb_info __initdata = {
  27. 	.displays	= &smdk2440_lcd_cfg,
  28. 	.num_displays	= 1,
  29. 	.default_display = 0,
  30.  
  31. #if 0
  32. 	/* currently setup by downloader */
  33. 	.gpccon		= 0xaa940659,
  34. 	.gpccon_mask	= 0xffffffff,
  35. 	.gpcup		= 0x0000ffff,
  36. 	.gpcup_mask	= 0xffffffff,
  37. 	.gpdcon		= 0xaa84aaa0,
  38. 	.gpdcon_mask	= 0xffffffff,
  39. 	.gpdup		= 0x0000faff,
  40. 	.gpdup_mask	= 0xffffffff,
  41. #endif
  42. //no
  43. //	.lpcsel		= ((0xCE6) & ~7) | 1<<4,
  44. };

这里NOTE：每个LCD屏幕的参数不一样，因此上面的参数会有所不同，这是需要移植的地方。

随后，我们看下在probe方法中调用的几个函数。首先是s3c2410fb_map_video_memory。

  1. /*
  2.  * s3c2410fb_map_video_memory():
  3.  *	Allocates the DRAM memory for the frame buffer.  This buffer is
  4.  *	remapped into a non-cached, non-buffered, memory region to
  5.  *	allow palette and pixel writes to occur without flushing the
  6.  *	cache.  Once this area is remapped, all virtual memory
  7.  *	access to the video memory should occur at the new region.
  8.  */
  9. static int __init s3c2410fb_map_video_memory(struct fb_info *info)
  10. {
  11. 	struct s3c2410fb_info *fbi = info->par;
  12. 	dma_addr_t map_dma;
  13. 	unsigned map_size = PAGE_ALIGN(info->fix.smem_len);
  14.  
  15. 	dprintk("map_video_memory(fbi=%p) map_size %u\n", fbi, map_size);
  16. 		/*分配DMA缓冲区，并保存DMA缓冲区虚拟地址*/
  17. 	info->screen_base = dma_alloc_writecombine(fbi->dev, map_size,
  18. 						   &map_dma, GFP_KERNEL);
  19.  
  20. 	if (info->screen_base) {
  21. 		/* prevent initial garbage on screen */
  22. 		dprintk("map_video_memory: clear %p:%08x\n",
  23. 			info->screen_base, map_size);
  24. 		memset(info->screen_base, 0x00, map_size);	/*DMA缓冲区清0*/
  25.  
  26. 		info->fix.smem_start = map_dma;	/*保存DMA缓冲区物理地址*/
  27.  
  28. 		dprintk("map_video_memory: dma=%08lx cpu=%p size=%08x\n",
  29. 			info->fix.smem_start, info->screen_base, map_size);
  30. 	}
  31.  
  32. 	return info->screen_base ? 0 : -ENOMEM;
  33. }


该函数根据fix.smem_len的大小，分配了一个DMA缓冲区，保存了该缓冲区的物理地址和虚拟地址。

接着是s3c2410fb_init_registers：

  1. /*
  2.  * s3c2410fb_init_registers - Initialise all LCD-related registers
  3.  */
  4. static int s3c2410fb_init_registers(struct fb_info *info)
  5. {
  6.     struct s3c2410fb_info *fbi = info->par;        /*par指向s3c2410fb_info*/
  7.     struct s3c2410fb_mach_info *mach_info = fbi->dev->platform_data;
  8.     unsigned long flags;
  9.     void __iomem *regs = fbi->io;
  10.     void __iomem *tpal;
  11.     void __iomem *lpcsel;
  12.  
  13.     if (is_s3c2412(fbi)) {
  14.         tpal = regs + S3C2412_TPAL;
  15.         lpcsel = regs + S3C2412_TCONSEL;
  16.     } else {
  17.         tpal = regs + S3C2410_TPAL;
  18.         lpcsel = regs + S3C2410_LPCSEL;
  19.     }
  20.  
  21.     /* Initialise LCD with values from haret */
  22.  
  23.     local_irq_save(flags);                        /*禁止所有中断*/
  24.  
  25.     /* modify the gpio(s) with interrupts set (bjd) */    /*初始化io管脚*/
  26.  
  27.     modify_gpio(S3C2410_GPCUP,  mach_info->gpcup,  mach_info->gpcup_mask);
  28.     modify_gpio(S3C2410_GPCCON, mach_info->gpccon, mach_info->gpccon_mask);
  29.     modify_gpio(S3C2410_GPDUP,  mach_info->gpdup,  mach_info->gpdup_mask);
  30.     modify_gpio(S3C2410_GPDCON, mach_info->gpdcon, mach_info->gpdcon_mask);
  31.  
  32.     local_irq_restore(flags);                    /*恢复中断*/
  33.  
  34.     dprintk("LPCSEL    = 0x%08lx\n", mach_info->lpcsel);    /*设置TCONSEL，禁止LPC3600*/
  35.     writel(mach_info->lpcsel, lpcsel);
  36.  
  37.     dprintk("replacing TPAL %08x\n", readl(tpal));
  38.  
  39.     /* ensure temporary palette disabled */
  40.     writel(0x00, tpal);    /*禁止调色板*/
  41.  
  42.     return 0;
  43. }
  44.  
  45. static inline void modify_gpio(void __iomem *reg,
  46.                    unsigned long set, unsigned long mask)
  47. {
  48.     unsigned long tmp;
  49.  
  50.     tmp = readl(reg) & ~mask;
  51.     writel(tmp | set, reg);
  52. }
最后是s3c2410fb_check_var： 

  1. /*
  2.  *	s3c2410fb_check_var():
  3.  *	Get the video params out of 'var'. If a value doesn't fit, round it up,
  4.  *	if it's too big, return -EINVAL.
  5.  *	检查变量的合法性
  6.  */
  7. static int s3c2410fb_check_var(struct fb_var_screeninfo *var,
  8. 			       struct fb_info *info)
  9. {
  10. 	struct s3c2410fb_info *fbi = info->par;			/*par指向s3c2410fb_info*/
  11. 	struct s3c2410fb_mach_info *mach_info = fbi->dev->platform_data;/*指向s3c2410fb_mach_info*/
  12. 	struct s3c2410fb_display *display = NULL;
  13. 	struct s3c2410fb_display *default_display = mach_info->displays +
  14. 						    mach_info->default_display;
  15. 	int type = default_display->type; 	/*S3C2410_LCDCON1_TFT*/
  16. 	unsigned i;
  17.  
  18. 	dprintk("check_var(var=%p, info=%p)\n", var, info);
  19.  
  20. 	/* validate x/y resolution */
  21. 	/* choose default mode if possible */			/*var中的成员在probe中设置*/
  22. 	if (var->yres == default_display->yres &&
  23. 	    var->xres == default_display->xres &&
  24. 	    var->bits_per_pixel == default_display->bpp)
  25. 		display = default_display;
  26. 	else
  27. 		for (i = 0; i < mach_info->num_displays; i++)
  28. 			if (type == mach_info->displays[i].type &&
  29. 			    var->yres == mach_info->displays[i].yres &&
  30. 			    var->xres == mach_info->displays[i].xres &&
  31. 			    var->bits_per_pixel == mach_info->displays[i].bpp) {
  32. 				display = mach_info->displays + i;
  33. 				break;
  34. 			}
  35.  
  36. 	if (!display) {
  37. 		dprintk("wrong resolution or depth %dx%d at %d bpp\n",
  38. 			var->xres, var->yres, var->bits_per_pixel);
  39. 		return -EINVAL;
  40. 	}
  41.  
  42. 	/* it is always the size as the display */
  43. 	var->xres_virtual = display->xres;
  44. 	var->yres_virtual = display->yres;
  45. 	var->height = display->height;
  46. 	var->width = display->width;
  47.  
  48. 	/* copy lcd settings */
  49. 	var->pixclock = display->pixclock;
  50. 	var->left_margin = display->left_margin;
  51. 	var->right_margin = display->right_margin;
  52. 	var->upper_margin = display->upper_margin;
  53. 	var->lower_margin = display->lower_margin;
  54. 	var->vsync_len = display->vsync_len;
  55. 	var->hsync_len = display->hsync_len;
  56.  
  57. 	fbi->regs.lcdcon5 = display->lcdcon5;
  58. 	/* set display type */
  59. 	fbi->regs.lcdcon1 = display->type;
  60.  
  61. 	var->transp.offset = 0;
  62. 	var->transp.length = 0;
  63. 	/* set r/g/b positions */
  64. 	switch (var->bits_per_pixel) {
  65. 	case 1:
  66. 	case 2:
  67. 	case 4:
  68. 		var->red.offset	= 0;
  69. 		var->red.length	= var->bits_per_pixel;
  70. 		var->green	= var->red;
  71. 		var->blue	= var->red;
  72. 		break;
  73. 	case 8:
  74. 		if (display->type != S3C2410_LCDCON1_TFT) {
  75. 			/* 8 bpp 332 */
  76. 			var->red.length		= 3;
  77. 			var->red.offset		= 5;
  78. 			var->green.length	= 3;
  79. 			var->green.offset	= 2;
  80. 			var->blue.length	= 2;
  81. 			var->blue.offset	= 0;
  82. 		} else {
  83. 			var->red.offset		= 0;
  84. 			var->red.length		= 8;
  85. 			var->green		= var->red;
  86. 			var->blue		= var->red;
  87. 		}
  88. 		break;
  89. 	case 12:
  90. 		/* 12 bpp 444 */
  91. 		var->red.length		= 4;
  92. 		var->red.offset		= 8;
  93. 		var->green.length	= 4;
  94. 		var->green.offset	= 4;
  95. 		var->blue.length	= 4;
  96. 		var->blue.offset	= 0;
  97. 		break;
  98.  
  99. 	default:
  100. 	case 16:
  101. 		if (display->lcdcon5 & S3C2410_LCDCON5_FRM565) { /*使用565格式*/
  102. 			/* 16 bpp, 565 format */
  103. 			var->red.offset		= 11;
  104. 			var->green.offset	= 5;
  105. 			var->blue.offset	= 0;
  106. 			var->red.length		= 5;
  107. 			var->green.length	= 6;
  108. 			var->blue.length	= 5;
  109. 		} else {
  110. 			/* 16 bpp, 5551 format */
  111. 			var->red.offset		= 11;
  112. 			var->green.offset	= 6;
  113. 			var->blue.offset	= 1;
  114. 			var->red.length		= 5;
  115. 			var->green.length	= 5;
  116. 			var->blue.length	= 5;
  117. 		}
  118. 		break;
  119. 	case 32:
  120. 		/* 24 bpp 888 and 8 dummy */
  121. 		var->red.length		= 8;
  122. 		var->red.offset		= 16;
  123. 		var->green.length	= 8;
  124. 		var->green.offset	= 8;
  125. 		var->blue.length	= 8;
  126. 		var->blue.offset	= 0;
  127. 		break;
  128. 	}
  129. 	return 0;
  130. }
  131.  
  132. /* Interpretation of offset for color fields: All offsets are from the right,
  133.  * inside a "pixel" value, which is exactly 'bits_per_pixel' wide (means: you
  134.  * can use the offset as right argument to <<). A pixel afterwards is a bit
  135.  * stream and is written to video memory as that unmodified.
  136.  *
  137.  * For pseudocolor: offset and length should be the same for all color
  138.  * components. Offset specifies the position of the least significant bit
  139.  * of the pallette index in a pixel value. Length indicates the number
  140.  * of available palette entries (i.e. # of entries = 1 << length).
  141.  */
  142. struct fb_bitfield {
  143.     __u32 offset;            /* beginning of bitfield    */
  144.     __u32 length;            /* length of bitfield        */
  145.     __u32 msb_right;        /* != 0 : Most significant bit is */ 
  146.                     /* right */ 
  147. };
该函数主要将板级信息s3c2410fb_display复制到对应的地方，然后根据RGB的模式设置位域。

4.3 fb_ops方法

在驱动程序中，定义了fb_ops，如下：

  1. static struct fb_ops s3c2410fb_ops = {
  2. 	.owner		= THIS_MODULE,
  3. 	.fb_check_var	= s3c2410fb_check_var,		/*检查变量的合法性*/
  4. 	.fb_set_par	= s3c2410fb_set_par,			/*将参数写入LCD控制器，该函数由帧缓冲核心调用*/
  5. 	.fb_blank	= s3c2410fb_blank,				/*该方法支持显示消隐和去消隐*/
  6. 	.fb_setcolreg	= s3c2410fb_setcolreg,		/*设置颜色寄存器*/
  7. 	.fb_fillrect	= cfb_fillrect,				/*用像素行填充矩形框，通用库函数*/
  8. 	.fb_copyarea	= cfb_copyarea,				/*将屏幕的一个矩形区域复制到另一个区域，通用库函数*/
  9. 	.fb_imageblit	= cfb_imageblit,			/*显示一副图像，通用库函数*/
  10. };

其中s3c2410fb_check_var在4.2节中已经分析过了，最后三个方法是通用库函数，在这里不作分析。
剩余三个也是驱动程序提供的，现在对这三个程序进行分析。

4.3. 1 s3c2410fb_set_par
  1. /*
  2.  *      s3c2410fb_set_par - Alters the hardware state.
  3.  *      @info: frame buffer structure that represents a single frame buffer
  4.  *		根据var中的值设置LCD控制器的寄存器
  5.  */
  6. static int s3c2410fb_set_par(struct fb_info *info)
  7. {
  8. 	struct fb_var_screeninfo *var = &info->var;
  9.  
  10. 	switch (var->bits_per_pixel) {
  11. 	case 32:
  12. 	case 16:
  13. 	case 12:
  14. 		info->fix.visual = FB_VISUAL_TRUECOLOR;
  15. 		break;
  16. 	case 1:
  17. 		info->fix.visual = FB_VISUAL_MONO01;
  18. 		break;
  19. 	default:
  20. 		info->fix.visual = FB_VISUAL_PSEUDOCOLOR;
  21. 		break;
  22. 	}
  23.  
  24. 	info->fix.line_length = (var->xres_virtual * var->bits_per_pixel) / 8; /* 320*16/8 = 640Bytes */
  25.  
  26. 	/* activate this new configuration */
  27.  
  28. 	s3c2410fb_activate_var(info);
  29. 	return 0;
  30. }

该函数根据像素的位数设置了视觉模式，本例为16为，使用真彩色。然后计算了每行的数据元素大小。共240行。

然后调用了s3c2410fb_activate_var来设置控制器并激活LCD。

s3c2410fb_activate_var函数如下：

  1. /* s3c2410fb_activate_var
  2.  *
  3.  * activate (set) the controller from the given framebuffer
  4.  * information
  5.  */
  6. static void s3c2410fb_activate_var(struct fb_info *info)
  7. {
  8. 	struct s3c2410fb_info *fbi = info->par;
  9. 	void __iomem *regs = fbi->io;
  10. 	int type = fbi->regs.lcdcon1 & S3C2410_LCDCON1_TFT; /*regs.lcdcon1在s3c2410fb_check_var设置*/
  11. 	struct fb_var_screeninfo *var = &info->var;
  12. 	int clkdiv = s3c2410fb_calc_pixclk(fbi, var->pixclock) / 2;
  13.  
  14. 	dprintk("%s: var->xres  = %d\n", __func__, var->xres);
  15. 	dprintk("%s: var->yres  = %d\n", __func__, var->yres);
  16. 	dprintk("%s: var->bpp   = %d\n", __func__, var->bits_per_pixel);
  17.  
  18. 	if (type == S3C2410_LCDCON1_TFT) {
  19. 		s3c2410fb_calculate_tft_lcd_regs(info, &fbi->regs);/*根据var，计算出控制寄存器需要设置的值*/
  20. 		--clkdiv;
  21. 		if (clkdiv < 0)
  22. 			clkdiv = 0;
  23. 	} else {
  24. 		s3c2410fb_calculate_stn_lcd_regs(info, &fbi->regs);
  25. 		if (clkdiv < 2)
  26. 			clkdiv = 2;
  27. 	}
  28.  
  29. 	fbi->regs.lcdcon1 |=  S3C2410_LCDCON1_CLKVAL(clkdiv);/*设置CLKVAL*/
  30.  
  31. 	/* write new registers */
  32.  
  33. 	dprintk("new register set:\n");
  34. 	dprintk("lcdcon[1] = 0x%08lx\n", fbi->regs.lcdcon1);
  35. 	dprintk("lcdcon[2] = 0x%08lx\n", fbi->regs.lcdcon2);
  36. 	dprintk("lcdcon[3] = 0x%08lx\n", fbi->regs.lcdcon3);
  37. 	dprintk("lcdcon[4] = 0x%08lx\n", fbi->regs.lcdcon4);
  38. 	dprintk("lcdcon[5] = 0x%08lx\n", fbi->regs.lcdcon5);
  39. 	/*把计算好的值填入LCD控制器中*/
  40. 	writel(fbi->regs.lcdcon1 & ~S3C2410_LCDCON1_ENVID,	
  41. 		regs + S3C2410_LCDCON1);						/*仍然禁止LCD*/
  42. 	writel(fbi->regs.lcdcon2, regs + S3C2410_LCDCON2);
  43. 	writel(fbi->regs.lcdcon3, regs + S3C2410_LCDCON3);
  44. 	writel(fbi->regs.lcdcon4, regs + S3C2410_LCDCON4);
  45. 	writel(fbi->regs.lcdcon5, regs + S3C2410_LCDCON5);
  46.  
  47. 	/* set lcd address pointers */
  48. 	s3c2410fb_set_lcdaddr(info);						/*设置LCD帧缓冲起始地址*/
  49.  
  50. 	fbi->regs.lcdcon1 |= S3C2410_LCDCON1_ENVID,
  51. 	writel(fbi->regs.lcdcon1, regs + S3C2410_LCDCON1);	/*使能LCD*/
  52. }
其中调用的三个函数如下： 
  1. static unsigned int s3c2410fb_calc_pixclk(struct s3c2410fb_info *fbi,
  2.                       unsigned long pixclk)
  3. {
  4.     unsigned long clk = clk_get_rate(fbi->clk);         /*获取当前时钟频率(Hz)*/
  5.     unsigned long long div;
  6.  
  7.     /* pixclk is in picoseconds, our clock is in Hz
  8.      *
  9.      * Hz -> picoseconds is / 10^-12
  10.      */
  11.  
  12.     div = (unsigned long long)clk * pixclk;
  13.     div >>= 12;            /* div / 2^12 */
  14.     do_div(div, 625 * 625UL * 625); /* div / 5^12 */
  15.  
  16.     dprintk("pixclk %ld, divisor is %ld\n", pixclk, (long)div);
  17.     return div;
  18. }
  19.  
  20. /* s3c2410fb_calculate_tft_lcd_regs
  21.  *
  22.  * calculate register values from var settings
  23.  */
  24. static void s3c2410fb_calculate_tft_lcd_regs(const struct fb_info *info,
  25.                          struct s3c2410fb_hw *regs)
  26. {
  27.     const struct s3c2410fb_info *fbi = info->par;
  28.     const struct fb_var_screeninfo *var = &info->var;
  29.  
  30.     switch (var->bits_per_pixel) {
  31.     case 1:
  32.         regs->lcdcon1 |= S3C2410_LCDCON1_TFT1BPP;
  33.         break;
  34.     case 2:
  35.         regs->lcdcon1 |= S3C2410_LCDCON1_TFT2BPP;
  36.         break;
  37.     case 4:
  38.         regs->lcdcon1 |= S3C2410_LCDCON1_TFT4BPP;
  39.         break;
  40.     case 8:
  41.         regs->lcdcon1 |= S3C2410_LCDCON1_TFT8BPP;
  42.         regs->lcdcon5 |= S3C2410_LCDCON5_BSWP |
  43.                  S3C2410_LCDCON5_FRM565;
  44.         regs->lcdcon5 &= ~S3C2410_LCDCON5_HWSWP;
  45.         break;
  46.     case 16:
  47.         regs->lcdcon1 |= S3C2410_LCDCON1_TFT16BPP;
  48.         regs->lcdcon5 &= ~S3C2410_LCDCON5_BSWP;
  49.         regs->lcdcon5 |= S3C2410_LCDCON5_HWSWP;
  50.         break;
  51.     case 32:
  52.         regs->lcdcon1 |= S3C2410_LCDCON1_TFT24BPP;
  53.         regs->lcdcon5 &= ~(S3C2410_LCDCON5_BSWP |
  54.                    S3C2410_LCDCON5_HWSWP |
  55.                    S3C2410_LCDCON5_BPP24BL);
  56.         break;
  57.     default:
  58.         /* invalid pixel depth */
  59.         dev_err(fbi->dev, "invalid bpp %d\n",
  60.             var->bits_per_pixel);
  61.     }
  62.     /* update X/Y info */
  63.     dprintk("setting vert: up=%d, low=%d, sync=%d\n",
  64.         var->upper_margin, var->lower_margin, var->vsync_len);
  65.  
  66.     dprintk("setting horz: lft=%d, rt=%d, sync=%d\n",
  67.         var->left_margin, var->right_margin, var->hsync_len);
  68.     /*
  69.         所有时序参数必须减1，因为在公式中:
  70.         Frame Rate = 1/ [ { (VSPW+1) + (VBPD+1) + (LIINEVAL + 1) + (VFPD+1) } x {(HSPW+1) + (HBPD +1)
  71.         + (HFPD+1) + (HOZVAL + 1) } x { 2 x ( CLKVAL+1 ) / ( HCLK ) } ]
  72.     */
  73.     regs->lcdcon2 = S3C2410_LCDCON2_LINEVAL(var->yres - 1) |
  74.             S3C2410_LCDCON2_VBPD(var->upper_margin - 1) |
  75.             S3C2410_LCDCON2_VFPD(var->lower_margin - 1) |
  76.             S3C2410_LCDCON2_VSPW(var->vsync_len - 1);
  77.  
  78.     regs->lcdcon3 = S3C2410_LCDCON3_HBPD(var->right_margin - 1) |
  79.             S3C2410_LCDCON3_HFPD(var->left_margin - 1) |
  80.             S3C2410_LCDCON3_HOZVAL(var->xres - 1);
  81.  
  82.     regs->lcdcon4 = S3C2410_LCDCON4_HSPW(var->hsync_len - 1);
  83. }
  84.  
  85. /* s3c2410fb_set_lcdaddr
  86.  *
  87.  * initialise lcd controller address pointers
  88.  */
  89. static void s3c2410fb_set_lcdaddr(struct fb_info *info)
  90. {
  91. 	unsigned long saddr1, saddr2, saddr3;
  92. 	struct s3c2410fb_info *fbi = info->par;
  93. 	void __iomem *regs = fbi->io;
  94.  
  95. 	saddr1  = info->fix.smem_start >> 1;  	/*帧缓冲区起始地址*/
  96. 	saddr2  = info->fix.smem_start;			
  97. 	saddr2 += info->fix.line_length * info->var.yres;
  98. 	saddr2 >>= 1;							/*帧缓冲区结束地址*/
  99.  
  100. 	saddr3 = S3C2410_OFFSIZE(0) |
  101. 		 S3C2410_PAGEWIDTH((info->fix.line_length / 2) & 0x3ff); /*offset = 0, pagewidth = 320*/
  102.  
  103. 	dprintk("LCDSADDR1 = 0x%08lx\n", saddr1);
  104. 	dprintk("LCDSADDR2 = 0x%08lx\n", saddr2);
  105. 	dprintk("LCDSADDR3 = 0x%08lx\n", saddr3);
  106.  
  107. 	writel(saddr1, regs + S3C2410_LCDSADDR1);
  108. 	writel(saddr2, regs + S3C2410_LCDSADDR2);
  109. 	writel(saddr3, regs + S3C2410_LCDSADDR3);
  110. }

s3c2410fb_calc_pixclk用于计算时钟频率。

s3c2410fb_calculate_tft_lcd_regs设置了LCD的控制寄存器。

s3c2410fb_set_lcdaddr设置了LCD的地址寄存器，该寄存器的设置请参考datasheet。

4.3. 2 s3c2410fb_blank

该方法完成消隐功能。

  1. /*
  2.  *      s3c2410fb_blank
  3.  *	@blank_mode: the blank mode we want.
  4.  *	@info: frame buffer structure that represents a single frame buffer
  5.  *
  6.  *	Blank the screen if blank_mode != 0, else unblank. Return 0 if
  7.  *	blanking succeeded, != 0 if un-/blanking failed due to e.g. a
  8.  *	video mode which doesn't support it. Implements VESA suspend
  9.  *	and powerdown modes on hardware that supports disabling hsync/vsync:
  10.  *
  11.  *	Returns negative errno on error, or zero on success.
  12.  *
  13.  */
  14. static int s3c2410fb_blank(int blank_mode, struct fb_info *info)
  15. {
  16.     struct s3c2410fb_info *fbi = info->par;
  17.     void __iomem *tpal_reg = fbi->io;
  18.  
  19.     dprintk("blank(mode=%d, info=%p)\n", blank_mode, info);
  20.  
  21.     tpal_reg += is_s3c2412(fbi) ? S3C2412_TPAL : S3C2410_TPAL;
  22.  
  23.     if (blank_mode == FB_BLANK_POWERDOWN) {    /*消隐*/
  24.         s3c2410fb_lcd_enable(fbi, 0);        /*禁止LCD*/
  25.     } else {
  26.         s3c2410fb_lcd_enable(fbi, 1);        /*启动LCD*/
  27.     }
  28.  
  29.     if (blank_mode == FB_BLANK_UNBLANK)        /*去消隐*/
  30.         writel(0x0, tpal_reg);                /*禁止temporary palette*/
  31.     else {                                    /*消隐*/
  32.         dprintk("setting TPAL to output 0x000000\n");
  33.         writel(S3C2410_TPAL_EN, tpal_reg);    /*使能temporary palette，颜色为黑色*/
  34.     }
  35.  
  36.     return 0;
  37. }
在消隐时，屏幕将全黑。

4.3.3 s3c2410fb_setcolreg

该函数的功能用于设置LCD的调色板。调色板的概念请看我的转帖：LCD调色板。

  1. static int s3c2410fb_setcolreg(unsigned regno,
  2.                    unsigned red, unsigned green, unsigned blue,
  3.                    unsigned transp, struct fb_info *info)
  4. {
  5.     struct s3c2410fb_info *fbi = info->par;    /*par指向s3c2410fb_info*/
  6.     void __iomem *regs = fbi->io;
  7.     unsigned int val;
  8.  
  9.     /* dprintk("setcol: regno=%d, rgb=%d,%d,%d\n",
  10.            regno, red, green, blue); */
  11.  
  12.     switch (info->fix.visual) {    
  13.     case FB_VISUAL_TRUECOLOR:    /*使用真彩色*/
  14.         /* true-colour, use pseudo-palette */
  15.  
  16.         if (regno < 16) {    /*16种颜色，为什么只用16种颜色???????????*/
  17.             u32 *pal = info->pseudo_palette;
  18.  
  19.             val  = chan_to_field(red,   &info->var.red);
  20.             val |= chan_to_field(green, &info->var.green);
  21.             val |= chan_to_field(blue,  &info->var.blue);
  22.  
  23.             pal[regno] = val;    /*保存颜色值*/
  24.         }
  25.         break;
  26.  
  27.     case FB_VISUAL_PSEUDOCOLOR:
  28.         if (regno < 256) {
  29.             /* currently assume RGB 5-6-5 mode */
  30.  
  31.             val  = (red   >>  0) & 0xf800;
  32.             val |= (green >>  5) & 0x07e0;
  33.             val |= (blue  >> 11) & 0x001f;
  34.  
  35.             writel(val, regs + S3C2410_TFTPAL(regno));
  36.             schedule_palette_update(fbi, regno, val);
  37.         }
  38.  
  39.         break;
  40.  
  41.     default:
  42.         return 1;    /* unknown type */
  43.     }
  44.  
  45.     return 0;
  46. }
  47. /* from pxafb.c */
  48. static inline unsigned int chan_to_field(unsigned int chan,
  49.                      struct fb_bitfield *bf)
  50. {    
  51.     /*下面用到的length和offset在s3c2410fb_check_var函数中设置*/
  52.     chan &= 0xffff;                /*取低16位*/
  53.     chan >>= 16 - bf->length;   /*取第length为到16位为有效位*/
  54.     return chan << bf->offset;    /*移动到相应的位置。*/
  55. }

我们使用的是真彩色，可以设置16种颜色，颜色的位域值通过调用chan_to_field获得，然后保存了颜色的值。但是比较奇怪的是，这里并没有将值保存到0x4d000400为起始的内存中，不知为何。 反而倒是在伪彩色模式下， 使用了writel(val, regs + S3C2410_TFTPAL(regno))写到内存中，然后调用schedule_palette_update函数来更新palette表。我们来看下。

  1. static void schedule_palette_update(struct s3c2410fb_info *fbi,
  2. 				    unsigned int regno, unsigned int val)
  3. {
  4. 	unsigned long flags;
  5. 	unsigned long irqen;
  6. 	void __iomem *irq_base = fbi->irq_base;
  7.  
  8. 	local_irq_save(flags);
  9.  
  10. 	fbi->palette_buffer[regno] = val;
  11.  
  12. 	if (!fbi->palette_ready) {
  13. 		fbi->palette_ready = 1;
  14.  
  15. 		/* enable IRQ */
  16. 		irqen = readl(irq_base + S3C24XX_LCDINTMSK);
  17. 		irqen &= ~S3C2410_LCDINT_FRSYNC;
  18. 		writel(irqen, irq_base + S3C24XX_LCDINTMSK);
  19. 	}
  20.  
  21. 	local_irq_restore(flags);
  22. }
这个函数的作用就是开启了LCD的帧同步中断，这个中断在VSYNC信号从无效变成有效时产生。当中断产生时，会调用在probe方法中注册的ISR。ISR如下： 

  1. static irqreturn_t s3c2410fb_irq(int irq, void *dev_id)
  2. {
  3. 	struct s3c2410fb_info *fbi = dev_id;
  4. 	void __iomem *irq_base = fbi->irq_base;
  5. 	unsigned long lcdirq = readl(irq_base + S3C24XX_LCDINTPND);
  6. b
  7. 	if (lcdirq & S3C2410_LCDINT_FRSYNC) {
  8. 		if (fbi->palette_ready)
  9. 			s3c2410fb_write_palette(fbi);
  10.  
  11. 		writel(S3C2410_LCDINT_FRSYNC, irq_base + S3C24XX_LCDINTPND);
  12. 		writel(S3C2410_LCDINT_FRSYNC, irq_base + S3C24XX_LCDSRCPND);
  13. 	}
  14.  
  15. 	return IRQ_HANDLED;
  16. }
  17.  
  18. static void s3c2410fb_write_palette(struct s3c2410fb_info *fbi)
  19. {
  20.     unsigned int i;
  21.     void __iomem *regs = fbi->io;
  22.  
  23.     fbi->palette_ready = 0;  /*清除ready标志*/
  24.  
  25.     for (i = 0; i < 256; i++) {
  26.         unsigned long ent = fbi->palette_buffer[i];
  27.         if (ent == PALETTE_BUFF_CLEAR)
  28.             continue;
  29.  
  30.         writel(ent, regs + S3C2410_TFTPAL(i));
  31.  
  32.         /* it seems the only way to know exactly
  33.          * if the palette wrote ok, is to check
  34.          * to see if the value verifies ok
  35.          */
  36.  
  37.         if (readw(regs + S3C2410_TFTPAL(i)) == ent)
  38.             fbi->palette_buffer[i] = PALETTE_BUFF_CLEAR;
  39.         else
  40.             fbi->palette_ready = 1;   /* retry */
  41.     }
  42. }
在中断函数中调用了s3c2410fb_write_palette，该函数对写入内存的颜色值进行检查。如果确认其已经写入，则将palette_buffer中的清除，否则retry。

5. 总结

本文对frambuffer子系统做了简单的介绍。frambuffer子系统的函数相当之多，在这里是不可能一一介绍的。本文首先介绍了主要的数据结构，

随后分析了frambuffer核心层，在核心层简单的分析了5个API函数，接着，对驱动层做了介绍，驱动层的大多数函数都给出了分析。




 

 

 

 

 

 

 

 

 


                

        
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