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

From: Peter Chen
Date: Wed Dec 12 2018 - 20:21:38 EST

> >
> > 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.

> - 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