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

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Date:	Sat, 18 Aug 2012 09:19:12 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Bruno Prémont <bonbons@...ux-vserver.org>
cc:	Jiri Kosina <jkosina@...e.cz>, <linux-input@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linux-fbdev@...r.kernel.org>
Subject: Re: [PATCH 0/7] HID: picoLCD updates

On Sat, 18 Aug 2012, Bruno Prémont wrote:

> Hi Jiri,
> 
> [CCing Alan Stern]
> 
> On Thu, 16 August 2012 Jiri Kosina <jkosina@...e.cz> wrote:
> > On Thu, 16 Aug 2012, Bruno Prémont wrote:
> > 
> > > > 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? 
> > 
> > Yup, through hid_hw_stop() -> usbhid_stop().
> > 
> > > 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.
> 
> Huh, after changing some of the hid-picolcd data in order to have less racy
> coupling between hid and framebuffer I'm now dying way too often in _mmx_memcpy
> and most of the time I don't get a (complete) trace...

There was a similar problem reported recently.  It turned out to be 
caused by a __devinitconst annotation attached to a usb_device_id 
table.

If there are any __devinit* annotations in the hid-picolcd driver, you 
should see if removing them helps.

Alan Stern

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