linux-kernel - Re: USB keyboard backlight powering down.

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Date:	Tue, 16 Oct 2012 10:29:30 -0700
From:	Sarah Sharp <sarah.a.sharp@...ux.intel.com>
To:	Dave Jones <davej@...hat.com>, Michael Spang <spang@...omium.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>, greno@...izon.net,
	Fedora Kernel Team <kernel-team@...oraproject.org>
Subject: Re: USB keyboard backlight powering down.

On Tue, Oct 16, 2012 at 11:20:23AM -0400, Dave Jones wrote:
> Gerry (CC'd) reported a bug to us that since 3.6.1, his illuminated
> Logitech USB keyboard doesn't light up until he hits a key, and then
> it immediately powers back off, defeating the purpose of having an
> illumated keyboard.

Does he have the udev bug that turns on auto-suspend for USB keyboards?
ISTR there was a Fedora bug that was fixed.

I ask because it sounds like the keyboard is suspended between key
strokes, and that powers down the light.  The USB hid driver doesn't
auto-suspend devices that have user toggleable LEDs.  For instance, it
won't suspend a keyboard if the caps lock or num lock key is set.  But
I'm betting the device doesn't advertise the backlight like the caps
lock key is advertised.

> Looking over the 3.6.1 changelog, I see this change, which sounds
> like it might be responsible ?

Did he actually do a git bisect?  Because that commit only applies to
when the system is suspended, not when the USB device is suspended.

Sarah Sharp

> commit ee537508bdc0c00b96ac497f3d82a68f820e6182
> Author: Michael Spang <spang@...omium.org>
> Date:   Fri Sep 14 13:05:49 2012 -0400
> 
>     Increase XHCI suspend timeout to 16ms
>     
>     commit a6e097dfdfd189b6929af6efa1d289af61858386 upstream.
>     
>     The Intel XHCI specification says that after clearing the run/stop bit
>     the controller may take up to 16ms to halt. We've seen a device take
>     14ms, which with the current timeout of 10ms causes the kernel to
>     abort the suspend. Increasing the timeout to the recommended value
>     fixes the problem.
>     
>     This patch should be backported to kernels as old as 2.6.37, that
>     contain the commit 5535b1d5f8885695c6ded783c692e3c0d0eda8ca "USB: xHCI:
>     PCI power management implementation".
>     
>     Signed-off-by: Michael Spang <spang@...omium.org>
>     Signed-off-by: Sarah Sharp <sarah.a.sharp@...ux.intel.com>
>     Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> 
> 
> Any thoughts on how we could prevent this generically, or is this
> something we're going to have to quirk around for specific devices we
> don't want to power down ?
> 
> 	Dave
> 
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