[Intel-gfx] [REGRESSION BISECTED] backlight control stops workin with 3.14 and later

[Daniel Vetter]

On Tue, Jul 22, 2014 at 8:42 AM, Hans de Goede <hdegoede at redhat.com> wrote:
> Hi Jani et al,
>
> A friend of mine Bertrik Sikken (in the Cc) his backlight control
> stopped working for him on his Samsung N150Plus netbook.
>
> I took a quick look, and the raw intel_backlight backlight interface
> works under 3.14, but the firmware samsung_laptop backlight interface,
> which is what most userspace apps will use by default, stops working
> in 3.14 .
>
> I've asked him to bisect this and the bisect points out this
> commit as the culprit:
>
> b35684b8fa94e04f55fd38bf672b737741d2f9e2 is the first bad commit
> commit b35684b8fa94e04f55fd38bf672b737741d2f9e2
> Author: Jani Nikula <jani.nikula at intel.com>
> Date:   Thu Nov 14 12:13:41 2013 +0200
>
>     drm/i915: do full backlight setup at enable time
>
>     We should now have all the information we need to do a full
>     initialization of the backlight registers.
>
>     v2: Keep QUIRK_NO_PCH_PWM_ENABLE for now (Imre).
>
>     Signed-off-by: Jani Nikula <jani.nikula at intel.com>
>     Reviewed-by: Imre Deak <imre.deak at intel.com>
>     Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
>
> Note that this laptop has an acpi_video backlight interface too,
> but that has been broken from the start and gets disabled by
> samsung-laptop based on dmi matching.

How does the intel backlight fare? Please test both 3.14 and 3.15 and
also test what happens when you blacklist the samsung-laptop driver
(if that's possible without wreaking the machine).

Also please grab latest intel-gpu-tools and record a register dump
with intel_reg_dump, again for both broken and working kernels.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch