Re: [REGRESSION BISECTED] backlight control stops workin with 3.14 and later

[Jani Nikula <jani.nikula@intel.com>]

On Wed, 23 Jul 2014, Hans de Goede <hdegoede@redhat.com> wrote:
> Hi,
>
> On 07/22/2014 08:52 AM, Daniel Vetter wrote:
>> On Tue, Jul 22, 2014 at 8:42 AM, Hans de Goede <hdegoede@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@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@intel.com>
>>>     Reviewed-by: Imre Deak <imre.deak@intel.com>
>>>     Signed-off-by: Daniel Vetter <daniel.vetter@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?
>
> That works fine with 3.14 .
>
>> Please test both 3.14 and 3.15 and
>
> We've tested with 3.14, please let us know if you also want
> Bertrik to test with 3.15.
>
>> also test what happens when you blacklist the samsung-laptop driver
>> (if that's possible without wreaking the machine).
>
> Then the vendor interface won't get promoted, acpi-video will load,
> and things likely will not work.
>
> Bertrik, can you try blacklisting the samsung-laptop module, then
> check /sys/class/backlight, the samsung_laptop dir should be gone
> replaced by an acpi_video0 (or some such) dir. Please try if that
> works. If that does not work, try booting with both the module
> blacklisted and "acpi_backlight=vendor" on the kernel commandline,
> then you should see only the intel-backlight under /sys/class/backlight
> and things should work.
>
>> Also please grab latest intel-gpu-tools and record a register dump
>> with intel_reg_dump, again for both broken and working kernels.
>
> Bertrik, can you do this please (without the blacklisting or special
> kernel commandline options).

Please attach dmesg with drm.debug=0xe module parameter set for some
recent kernel.

BR,
Jani.


>
> Regards,
>
> Hans

-- 
Jani Nikula, Intel Open Source Technology Center