RE: [PATCH v1 2/2] usb:cdns3 Add Cadence USB3 DRD Driver

[Peter Chen]

> >
> > Felipe, I use Dynamic Debug for debugging, and show debug messages
> > with "dmesg" after testing/debugging. I see dwc3 using trace,  any
> > benefits for switching to trace?
> 
> The benefits I see are
> 

Thanks, bin.

> - *by default*, the debug log doesn't have to go through uart console,
>   which is slow.
> 
>   I typically 'cat trace_pipe' from a telnet which is much faster then
>   uart. But Dynamic Debug log by default got printed on uart, I have to
>   set printk level to not print them, which is an extra step.
> 

It depends on the rootfs's setting. By default, the debug message level should be off (
console level = 7)

> - tracepoint uses one place to decode the message vs DD has to repeat
>   the similar print statement in the code; and tracepoint decodes it
>   offline which reduce the kernel runtime overhead too.
> 

offline? You mean when you run "cat trace_pipe"?

> - with tracepoint, it is easier to turn on debug for a specific group of
>   messages.
> 

The DD can, but we don't do it often.

https://www.kernel.org/doc/html/latest/admin-guide/dynamic-debug-howto.html?highlight=dynamic%20debug

> - you can adjust the ftrace buffer size at runtime. can we do that for
>   printk? I don't remember.

It may can't. The log buf can only be changed by bootargs: log_buf_len

Peter