[Nouveau] Nouveau Digest, Vol 131, Issue 3

[Ilia Mirkin]

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!

  -ilia