Re: [PATCH xf86-video-amdgpu 0/7] Enabling Color Management - Round 3

["Michel Dänzer" <michel-otUistvHUpPR7s880joybQ@public.gmane.org>]

On 2018-06-08 04:33 PM, Michel Dänzer wrote:
> On 2018-06-08 12:21 AM, Leo Li wrote:
>> On 2018-06-06 01:03 PM, Michel Dänzer wrote:
>>> On 2018-06-06 06:01 PM, Michel Dänzer wrote:
>>>>
>>>> Running Xorg in depth 30[0] results in completely wrong colours
>>>> (everything has a red tint) with current kernels. I think this is
>>>> because DC now preserves the gamma LUT values, but xf86-video-amdgpu
>>>> never sets them at depth 30, so the hardware is still using values for
>>>> 24-bit RGB.
>>>
>>> Actually, looks like I made a mistake in my testing before; this issue
>>> only occurs as of patch 6 of this series.
>>
>> It seems to be caused by legacy gamma being disabled on depth 30. When
>> that's the case, the gamma_set() hook is set to null. RandR won't
>> compute the legacy LUT, causing LUT interpolation/composition to spit
>> out an invalid LUT. I verified this by commenting out the `pScrn->depth
>> == 30` conditionals guarding the legacy gamma features (in pre_init, and
>> mode_major).
>>
>> I'm not certain of the best way to fix this. Would it make sense to
>> enable legacy gamma on 30bpp if non-legacy is supported? We can do that
>> since legacy gamma gets interpolated/composed to non-legacy.
>>
>> However, it doesn't make sense when you look at the LUT size, since
>> legacy gamma supports only 256 elements (should be 1024 on depth 30?)
>> In which case we can skip interpolation/composition altogether.
> 
> Right, we'll probably need to increase the RandR LUT size as well at
> depth 30.
> 
> 
> Anyway, let's not hold up this patch series over this. Simply keep all
> this code disabled (i.e. same as if the kernel didn't expose the
> properties) at depth 30 for now.

Or, if there's a straightforward way to expose the properties while
ignoring the RandR LUT at depth 30, that's another option for this series.


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