SDK: ti-processor-sdk-linux-am335x-evm-05.03.00.07.
Hi Marisol! Nice to see a familiar name from my days at Newark. I'm
part of the BeagleBoard.org Foundation so happy to help where I can.
Based on am335x in the Subject, are you working with a BeagleBone Black?
I want to have more debug ouputs in the console window during the Linux kernel booting so that I can trace for example MMC driver loading process.
Added some printk() into the kernel, for example printk("this function is called \n"). After successful compiling and loading the kernel unfortunately I can't see the
expected output message "this function is called" in the console window.
It is generally easier to use the "pr_" helper functions:
https://elinux.org/Debugging_by_printing
pr_err() uses KERN_ERR level should always print regardless of the
printk log level. KERN_ERR is not a good practice for debug output,
but it does eliminate the chance that the log level is filtering out
your print statements.
Try adding this:
pr_err("DEBUG: start name_of_function()");
If you don't see that in dmesg, then it is likely that the function
you put that in is never actually called.
I also tried
echo 8 > /proc/sys/kernel/printk
dmesg
after login but the same results.
Is there any configuration missing in .config file?
level 8 should be sufficient but it is easier if you just set the
level in the .config before you compile your kernel.
CONFIG_PRINTK_TIME=y
CONFIG_CONSOLE_LOGLEVEL_DEFAULT=7
CONFIG_CONSOLE_LOGLEVEL_QUIET=7
CONFIG_MESSAGE_LOGLEVEL_DEFAULT=7
You probably also want to make sure dynamic debugging is enabled:
CONFIG_DYNAMIC_DEBUG=y
Dynamic debugging is a neat feature where you can chose to see more
debug information for a particular source code file:
https://linux-kernel-labs.github.io/refs/heads/master/labs/kernel_modules.html?highlight=config_dynamic_debug#dynamic-debugging
Sometimes you don't even need to add in your own debug print
statements, you just need to enable the dynamic debug output that is
already built-in to a driver or subsystem.
I also see brcmf_dbg() in kernel files, how can I activate it?
Are you trying to debug a Broadcom wifi driver?
Taking a look at Elixir to search the kernel code:
It looks like CONFIG_BRCM_TRACING will enable debug output:
Try setting that in your .config:
https://cateee.net/lkddb/web-lkddb/BRCM_TRACING.html
While it is technically to enable function tracing for the driver, it
looks like it will cause brcmf_dbg() to be defined.
Now the individual invocations of brcmf_dbg() will have a log level
associated with them. It appears that level can be set as kernel
module parameter:
This forum post has more information:
It indicates this can be set while the module is loaded via:
echo 6 > /sys/module/brcmfmac/parameters/debug
Let me me now how it goes.
Thanks,
Drew
