今天终于将dev_dbg信息输出了，为了以后方便查找，特记录下来：
1、修改缺省信息的宏定义级别(kernel\include\linux\printk.h文件内)：
/* printk's without a loglevel use this.. */
#define MESSAGE_LOGLEVEL_DEFAULT CONFIG_MESSAGE_LOGLEVEL_DEFAULT
/* We show everything that is MORE important than this.. */
#define CONSOLE_LOGLEVEL_SILENT 0 /* Mum's the word */
#define CONSOLE_LOGLEVEL_MIN 1 /* Minimum loglevel we let people use */
#define CONSOLE_LOGLEVEL_QUIET 4 /* Shhh ..., when booted with "quiet" */
#define CONSOLE_LOGLEVEL_DEFAULT 8 /* anything MORE serious than KERN_DEBUG */
#define CONSOLE_LOGLEVEL_DEBUG 10 /* issue debug messages */
#define CONSOLE_LOGLEVEL_MOTORMOUTH 15 /* You can't shut this one up *///#define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
将值改为8
#define DEFAULT_CONSOLE_LOGLEVEL 8 /* anything MORE serious than KERN_DEBUG */
该行表示只有打印级别高于DEFAULT_CONSOLE_LOGLEVEL(值小于DEFAULT_CONSOLE_LOGLEVEL)的打印才会出现在终端上。
而 KERN_DEBUG也为7，所以我们的调试不会直接打印出来
kernel\include\linux\kern_levels.h
#define KERN_SOH "\001" /* ASCII Start Of Header */
#define KERN_SOH_ASCII '\001'
#define KERN_EMERG KERN_SOH "0" /* system is unusable */
#define KERN_ALERT KERN_SOH "1" /* action must be taken immediately */
#define KERN_CRIT KERN_SOH "2" /* critical conditions */
#define KERN_ERR KERN_SOH "3" /* error conditions */
#define KERN_WARNING KERN_SOH "4" /* warning conditions */
#define KERN_NOTICE KERN_SOH "5" /* normal but significant condition */
#define KERN_INFO KERN_SOH "6" /* informational */
#define KERN_DEBUG KERN_SOH "7" /* debug-level messages */2、在要输出dev_dbg信息的*.c文件的最前面添加：
#define DEBUG 1
因为dev_dbg的宏定义在kernel\include\linux\device.h，而这文件通常被其它文件引用，在本BSP内被kernel/include/linux/platform_device.h引用，因此必须在引用这头文件之前定义DEBUG。