Re: No backlight since linux-4.2.4 - drivers/gpu/drm/radeon/atombios_encoders.c

From: "Michel Dänzer" <michel@daenzer.net>
To: Michael Burian <michael.burian@sbg.at>
Cc: "dri-devel@lists.freedesktop.org" <dri-devel@lists.freedesktop.org>
Subject: Re: No backlight since linux-4.2.4 - drivers/gpu/drm/radeon/atombios_encoders.c
Date: Tue, 27 Oct 2015 18:17:14 +0900	[thread overview]
Message-ID: <562F411A.60906@daenzer.net> (raw)
In-Reply-To: <562F395C.2080109@sbg.at>

On 27.10.2015 17:44, Michael Burian wrote:
> On 10/27/15 03:36, Michel Dänzer wrote:
>>>
>>> [0] contains dmesg output with your patch applied (which fixes the backlight issue)
>>
>> This is very surprising: The patch just adds some debugging output, it's
>> not supposed to have any functional effect. Also, I don't see any of the
>> debugging output added by the patch in
>> dmesg-4.3.0-rc7-00003-g85051e2-dirty-2015-10-26-11-00-41-radeon-bl-debug.
>>
> 
>> Are you sure that my patch was actually applied to the radeon driver
>> when generating that file? Did you update the initrd with the patched
>> radeon.ko?
>>
> 
> the build was done using "make -j4 deb-pkg" on a better equipped machine,
> .deb packages were copied over and installed - maybe something interesting
> happened
> 
> AFAICT the patch should have been applied, at least it was shown with
> git diff and the -dirty suffix was added by the build system, not me.
> All graphics related drivers are compiled in (=y) rather than as
> modules (=m) in .config.
> 
> Another thing I tried yesterday was to add the old way right below the new one
> (this fixes the backlight issue) enclosed by some debug statements that indicate
> start / stop of the old / new method. (see atomdebug.diff - should be applied against
> mainline)

I'm not familiar with the ATOM bytecode, but since the number of
bytecode instructions executed seems the same in both cases, I suspect
that dig->backlight_level == 0 => ATOM_LCD_BLOFF is executed. (The
debugging output in my patch would have provided all of this information
and more, but there wasn't any of it in the dmesg you provided)

I guess the question then becomes how dig->backlight_level is (supposed
to be) initialized.

What values do the following files contain in the broken and working cases?

/sys/class/backlight/radeon_bl0/bl_power
/sys/class/backlight/radeon_bl0/brightness
/sys/class/backlight/radeon_bl0/actual_brightness
/sys/class/backlight/radeon_bl0/max_brightness

-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer
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