Strange effect with i915 backlight controller

[Daniel Mack]

On 11/08/2011 01:57 AM, Daniel Mack wrote:
> Didn't get any response yet, hence copying LKML for a broader audience.

Nobody, really?

This is a rather annoying regression, as touching the brightness keys
appearantly switches off the whole machine. I'm sure this is trivial to
fix, I just don't have the insight of this driver and the chipset.

Any pointer greatly appreciated, and I can test patches.


Thanks,
Daniel



> 
> On 11/04/2011 03:36 PM, Daniel Mack wrote:
>> I'm facing a bug on a Samsung X20 notebook which features an i915
>> chipset (output of 'lspci -v' attached).
>>
>> The effect is that setting the backlight to odd values causes the value
>> to be misinterpreted. Harald Hoyer (cc:) had the same thing on a Netbook
>> (I don't recall which model it was).
>>
>> So this will turn the backlight to full brightness:
>>
>> # cat /sys/class/backlight/intel_backlight/max_brightness
>> 29750
>> # echo 29750 > /sys/class/backlight/intel_backlight/brightness
>>
>> However, writing 29749 will turn the display backlight off, and 29748
>> appears to be the next valid lower value.
>>
>> It seems like the IS_PINEVIEW() branch in
>> drivers/gpu/drm/i915/intel_panel.c:intel_panel_actually_set_backlight()
>> could do the right thing, but this code is written for an entirely
>> different model, right?
>>
>> I can reproduce this on 3.0 and 3.1 vanilla as well as with the current
>> mainline git.
>>
>> Let me know if there is any patch that I can test.
>>
>>
>> Thanks,
>> Daniel
>