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 11:37:21 +0000
From:	"Du, Changbin" <changbin.du@...el.com>
To:	Felipe Balbi <balbi@...nel.org>
CC:	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v4 2/2] usb: dwc3: add debugfs node to dump FIFO/Queue
 available space

> > 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

Thanks for the sharing, this is a good approach to capture dynamic
behaviors. But a dump of current state has below advantages:
1. a quick view for the pending transfers. Then we can quickly 
     checking the transfer status.
2. no side-effect. This is important in some case. We usually
    encounter some transfer issues but very hard to reproduce
    it. But we cannot enable trace all the time since performance
    concern. Then I thought it was so great if I can have a look for
    the trb status. :)

Best Regards,
Du, Changbin