Today, I finally output the dev_dbg information. For the convenience of searching in the future, I specially record it:
1. Modify the macro definition level of the default information (in the kernel\include\linux\printk.h file):
/* 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 */
Change the value to 8
#define DEFAULT_CONSOLE_LOGLEVEL 8 /* anything MORE serious than KERN_DEBUG */
This line indicates that only prints with a print level higher than DEFAULT_CONSOLE_LOGLEVEL (with a value smaller than DEFAULT_CONSOLE_LOGLEVEL ) will appear on the terminal.
And KERN_DEBUG is also 7, so our debugging will not be printed directly
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. Add at the front of the *.c file to output dev_dbg information:
#define DEBUG 1
Because the macro definition of dev_dbg is in kernel\include\linux\device.h, and this file is usually referenced by other files, it is referenced by kernel/include/linux/platform_device.h in this BSP, so it must be defined before referencing this header file DEBUG.