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 11:58:47 +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

> Hi,
> 
> "Du, Changbin" <changbin.du@...el.com> writes:
> >> > 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. :)
> 
> yeah, okay. We can definitely add "current state" of almost anything,
> but if you need history, then debugfs is not the best interface and I'd
> point you to tracepoints ;-)
> 
> I'll think about how I can add TRB state, seems like we'd need to dump
> the entire endpoint ring, and that's 256 TRBs per endpoint :-p Then we
> also need to know endpoint's dequeue and enqueue pointer. Oh well, let
> me get this first setup of files out of the way, then we can add more
> later much more easily.
> 
> --
> Balbi

Okay, things need finish step by step. Thank you, Balbi. ( �b- �b)つロ

Best Regards,
Du, Changbin