[Intel-gfx] [PATCH 0/4] drm/i915: Re: clear up backlight inversion confusion on gen4

Carsten Emde C.Emde at osadl.org
Thu Apr 26 18:48:33 CEST 2012

On 04/23/2012 06:55 PM, Carsten Emde wrote:
> On 04/23/2012 05:56 PM, Daniel Vetter wrote:
>> On Mon, Apr 23, 2012 at 05:38:27PM +0200, Carsten Emde wrote:
>>> On 04/23/2012 05:22 PM, Daniel Vetter wrote:
>> Ok, so the polarity bit does work as advertised. But I still don't
>> understand how your machine works,
Let's go ahead and summarize what we have up to now.

1. With KMS enabled, the backlight panel of the Acer Aspire 5734Z remains dark.

2. Further evaluation showed that the brightness is inverted on this machine,
i.e. while setting the Legacy Backlight Brightness (LBB) register to 0x0
normally causes the backlight to be turned off, and 0xFF causes the backlight
to be set to 100% intensity, the Acer Aspire 5734Z turns the backlight off at
0xFF and sets it to maximum intensity at 0.

3. In a first step, a quirk was introduced to cope with this particular oddity.

4. Daniel Vetter found out there is a bit in the 2nd backlight control register
(BLC_PWM_CTL2) that indicates panel backlight brightness is inverted.

5. On the Acer Aspire 5734Z, however, this bit is not set.

6. Chris Wilson found out that Daniel's bit #28 sometimes could be bit #29.

7. On the Aspire 5734Z, bit #29 is set.

As a conclusion, I have prepared a patch series that
- uses Danieĺ's patch to invert brightness, if required,
- reverts the quirk to invert backlight brightness,
- introduces a new quirk to indicate bit #29 instead of #28 is used,
- marks the Acer Aspire 5734Z to use the quirked bit.

With these patches applied, the Acer Aspire 5734Z works.


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