[Nouveau] Nouveau Digest, Vol 131, Issue 3

[Ilia Mirkin]

On Mon, Mar 5, 2018 at 7:33 AM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
> On Mon, Mar 5, 2018 at 1:17 AM, Mario Kleiner
> <mario.kleiner.de at gmail.com> wrote:
>> On 03/03/2018 12:59 AM, Ilia Mirkin wrote:
>>>
>>> On Fri, Mar 2, 2018 at 6:46 PM, Mario Kleiner
>>> <mario.kleiner.de at gmail.com> wrote:
>>>>
>>>> On 03/02/2018 11:29 PM, Ilia Mirkin wrote:
>>>>>
>>>>> OK, so even if you're passing 1024 to xf86HandleColormaps, gamma_set
>>>>> still only gets called with a 256-entry LUT? If so, that works nicely
>>>>> here, but is not intuitive :)
>>>>
>>>>
>>>> Yes. Lots of remapping in the server, i get dizzy everytime i look at it,
>>>> and forget almost immediately how stuff fits together when i don't look
>>>> at
>>>> it. Anyway, the final downsampling from 1024 -> 256 hw lut happens in
>>>> xf86RandR12CrtcComputeGamma(), see
>>>>
>>>>
>>>> https://cgit.freedesktop.org/xorg/xserver/commit/?id=b5f9fcd50a999a00128c0cc3f6e7d1f66182c9d5
>>>>
>>>> for the latest. I'll propose that one to get cherry-picked into the
>>>> server-1.19 branch as well.
>>>
>>>
>>> Hrmph. That means we should try to adjust the gamma_set helper to do
>>> the sampling when receiving a 1024-sized LUT, if people will use older
>>> X servers (seems likely). Should hopefully be straightforward, to
>>> handle just that one case.
>>
>>
>> I think we never receive anything but a 256 slot LUT via gamma_set afaics?
>> The server initializes xf86Crtc's gamma_size to 256 at startup, and none of
>> the ddx'es ever overrides that with actual info from the kernel.
>>
>> What happens on older servers without that patch iff color depth 30 is
>> selected is simply that the gamma table updates no-op, so the server runs
>> with an identity gamma table setup at startup. Not perfect, but also not
>> that bad, given that probably most people run their setups with a gamma of
>> 1.0 anyway. At default depth 24 stuff works as usual.
>
> Ah OK. That's not so bad. I'll try to play around with it this week.
> Thanks for the explanation!

I just tested this out against xorg 1.19.5. With your patch, I get an
extremely dark screen. I think it's just getting the first 256 of the
1024 values (I checked -- gamma_set is still only getting 256 values).
So we have to do something a bit cleverer to fix this scenario...
ideas?

  -ilia