USB keyboard backlight powering down.

Dave Jones
2012-10-16T15:20:39Z

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.

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

commit ee537508bdc0c00b96ac497f3d82a68f820e6182
Author: Michael Spang <spang@chromium.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@chromium.org>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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