linux-kernel - RE: [PATCH v4 2/2] usb: dwc3: add debugfs node to dump FIFO/Queue available space

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Date:	Thu, 14 Apr 2016 14:18:43 +0300
From:	Felipe Balbi <balbi@...nel.org>
To:	"Du\, Changbin" <changbin.du@...el.com>
Cc:	"gregkh\@linuxfoundation.org" <gregkh@...uxfoundation.org>,
	"linux-usb\@vger.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v4 2/2] usb: dwc3: add debugfs node to dump FIFO/Queue available space


Hi,

"Du, Changbin" <changbin.du@...el.com> writes:
> Hi, Balbi.
>
> Feel free to change it, I may not have enough time on this currently.
> "per-endpoint directory" is great idea, then we do not need find out
> wanted info from one big file, but just go to specific dir. 

that was the idea, glad you liked it ;-)

> Btw, I'd mention that not all out ep has a rx fifo. So in my original patch,

yeah, rx fifos are dynamically allocated by the HW itself, AFAICT.

> not all FIFO/Queue info are valid. We need pick out the real info we need.
> And I didn't find any method to read the FIFO map.
>
> At last, comparing with the FIFO/Queue info, I think software transfer
> Requests list, TRBs info, EVENTs history are much more useful for debugging
> the driver. If you can also add these info to each EP folder, that is awesome!
> :)

I'll think about adding these but for the lifetime of requests and trbs
and events, etc, we have tracepoints for that. I usually do the
following when debugging:

# mount -t debugfs none /sys/kernel/debug
# cd /sys/kernel/debug/tracing
# echo 2048 > buffer_size_kb
# echo 1 > events/dwc3/enable

(do something to break it)

# cp trace /mnt/sdcard # or something like that

then read the file. You can make it as large or as small as you like
(given some constraints, of course ;-) but I've had no issues allocating
128MiB in the past.

-- 
balbi

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