Re: USB keyboard backlight powering down.

From: Sarah Sharp
Date: Tue Oct 16 2012 - 13:29:20 EST

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@xxxxxxxxxxxx>
> 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@xxxxxxxxxxxx>
> Signed-off-by: Sarah Sharp <>
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> 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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