Re: [PATCH 1/4] drm/i915: save/restore the legacy backlight control

["Indan Zupancic" <indan@nul.nu>]

On Tue, August 28, 2012 16:14, Daniel Vetter wrote:
> On Tue, Aug 28, 2012 at 03:56:31PM +0200, Indan Zupancic wrote:
>> Hello,
>>
>> On Tue, August 28, 2012 08:53, Jani Nikula wrote:
>> > From: Daniel Vetter <daniel.vetter@ffwll.ch>
>> >
>> > This is a prep patch to stop drm/i915 from changing the LBPC registers
>> > itself - but we still need to properly save/restore it on
>> > suspend/resume.
>> >
>> > Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
>> > Signed-off-by: Jani Nikula <jani.nikula@intel.com>
>> > ---
[...]
>> It seems weird that LBPC wouldn't be restored during resume by some BIOSes,
>> is this really necessary?
>
> ba3820ade317ee36e496b9b40d2ec3987dd4aef0 claims so. But that commit
> managed to put too many things into the same thing unfortunately.

Is that the right SHA? Because that just reverts my combination mode
removal patch. Assuming it is the right commit, then I think it's
incorrect in saying that it caused backlight dimming problems after
resume. That particular problem was caused by a bogus shift. The
problems caused by removing the mode was a lower max brightness
and/or less brightness levels.

By the way, saving LBPC only makes sense if it's done before it was
set to 0 to disable the panel. I don't know if the current code does
the right thing, I haven't looked at it for a while.

Greetings,

Indan