Android固件加载出错（load failed with error -2)_direct firmware load failed with error -2

         在Android下移植一个降噪模块的驱动到另一个平台,加载固件的时候报错

[  137.659357] xxxxx 0-002c: Direct firmware load failed with error -2
 
[  137.665773] xxxxx 0-002c: Falling back to user helper

查看-2代表的错误码可知，-2代表找不到文件，可是文件的确在/system/lib/firmware下，为什么找不到呢？

include/uapi/asm-generic/errno-base.h

#define	EPERM		 1	/* Operation not permitted */
#define	ENOENT		 2	/* No such file or directory */
#define	ESRCH		 3	/* No such process */
#define	EINTR		 4	/* Interrupted system call */
#define	EIO		 5	/* I/O error */
#define	ENXIO		 6	/* No such device or address */
#define	E2BIG		 7	/* Argument list too long */
#define	ENOEXEC		 8	/* Exec format error */
#define	EBADF		 9	/* Bad file number */
#define	ECHILD		10	/* No child processes */
#define	EAGAIN		11	/* Try again */
#define	ENOMEM		12	/* Out of memory */
#define	EACCES		13	/* Permission denied */
#define	EFAULT		14	/* Bad address */
#define	ENOTBLK		15	/* Block device required */
#define	EBUSY		16	/* Device or resource busy */
#define	EEXIST		17	/* File exists */
#define	EXDEV		18	/* Cross-device link */
#define	ENODEV		19	/* No such device */
#define	ENOTDIR		20	/* Not a directory */
#define	EISDIR		21	/* Is a directory */
#define	EINVAL		22	/* Invalid argument */
#define	ENFILE		23	/* File table overflow */
#define	EMFILE		24	/* Too many open files */
#define	ENOTTY		25	/* Not a typewriter */
#define	ETXTBSY		26	/* Text file busy */
#define	EFBIG		27	/* File too large */
#define	ENOSPC		28	/* No space left on device */
#define	ESPIPE		29	/* Illegal seek */
#define	EROFS		30	/* Read-only file system */
#define	EMLINK		31	/* Too many links */
#define	EPIPE		32	/* Broken pipe */
#define	EDOM		33	/* Math argument out of domain of func */
#define	ERANGE		34	/* Math result not representable */

找到driver/base/firmware_class.c文件，可以看到

static char fw_path_para[256];
static const char * const fw_path[] = {
	fw_path_para,
	"/lib/firmware/updates/" UTS_RELEASE,
	"/lib/firmware/updates",
	"/lib/firmware/" UTS_RELEASE,
	"/lib/firmware"
};
 
/*
 * Typical usage is that passing 'firmware_class.path=$CUSTOMIZED_PATH'
 * from kernel command line because firmware_class is generally built in
 * kernel instead of module.
 */
module_param_string(path, fw_path_para, sizeof(fw_path_para), 0644);
MODULE_PARM_DESC(path, "customized firmware image search path with a higher priority than default path");
 

      原来是固件的位置不对,在Android的文件系统下，根目录下并没有lib文件夹啊，当然通过软链接的方式实现固件加载,在init.rc中将/system/lib/软链接(symlink)到/lib。当然，直接修改源码，想从什么路径进行加载都行啊。还有一个路径，fw_path_path就是读取内核命令行（/proc/cmdline）指定的固件路径，将firmware_class.path=$CUSTOMIZED_PATH'添加到内核命令行中就行。其他Android版本的内核固件路径可参考http://blog.csdn.net/mike8825/article/details/51841871