linux-kernel - Re: [PATCH 0/7] HID: picoLCD updates

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Date:	Thu, 16 Aug 2012 18:30:21 +0200
From:	Bruno Prémont <bonbons@...ux-vserver.org>
To:	Jiri Kosina <jkosina@...e.cz>
Cc:	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-fbdev@...r.kernel.org
Subject: Re: [PATCH 0/7] HID: picoLCD updates

On Wed, 15 August 2012 Jiri Kosina <jkosina@...e.cz> wrote:
> On Wed, 15 Aug 2012, Bruno Prémont wrote:
> > > I see. Alan Stern has fixed a huge pile of things in this area in 3.6-rc1. 
> > > I have expected all of those to actually be on theoretical problems not 
> > > ever having happened in the wild, but it might be that you are actually 
> > > chasing on of those.
> > >
> > > Could you please retest with latest Linus' tree (or at least eb055fd0560b) 
> > > to see whether this hasn't actually been fixed already by Alan's series?
> > 
> > I've started trying that out, it seems Alan's work improved things.
> > 
> > For the first few attempts I have not seen SLAB corruptions, though after
> > a few rounds I hit accumulation of the following messages:
> > [  297.174828] hid-picolcd 0003:04D8:C002.0003: output queue full
> > [  297.181098] hid-picolcd 0003:04D8:C002.0003: output queue full
> > [  297.187820] hid-picolcd 0003:04D8:C002.0003: output queue full
> > [  297.194087] hid-picolcd 0003:04D8:C002.0003: output queue full
> > 
> > with sporadically in between:
> > [  292.668019] hid-picolcd 0003:04D8:C002.0003: usb_submit_urb(out) failed: -1
> > 
> > At first glance I think the queue filling up and never draining is caused
> > by hid_hw_stop() stalling the queue and the time between both being just too
> > short.
> 
> I don't really understand this explanation. Once usb_kill_urb() returns, 
> the URB should be available for future use (and therefore all queues 
> completely drained).

I won't have time today to check, though my guess is that on each
echo $usb-id > bind; echo $usb-id > unbind
under /sys/bus/hid/drivers/hid-picolcd/ the USB urb queue fills a bit does
not get cleared.

Is usb_kill_urb() called when unbinding just the specific hid driver? If so
my short timing between bind/unbind must be triggering something else...

Otherwise I'm missing something as at first time I got no "output queue full"
messages, but as I repeated the bind/unbind sequences the prints per bind/unbind
iteration increased in number.

Anyhow, on Friday evening/week-end I will continue digging and report back with my
findings.

Thanks,
Bruno
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