[Nouveau] Nouveau Digest, Vol 131, Issue 3

[Mario Kleiner]

On Sat, Apr 28, 2018 at 7:22 PM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
> On Thu, Mar 8, 2018 at 11:29 PM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
>> 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?
>
> Mario,
>
> Have you given this any thought? Is there a way to detect one or the
> other scenario? I'd rather not put something in where we check the X
> version at compile time. Did the ABI get bumped in 1.20 perhaps?
>
>   -ilia

Nope, haven't had time to retest on 1.19, too much "fun" trying to
tame all those new server 1.20 bugs which got in the way of depth 30
stuff.
I think the video ABI got bumped in 1.20.

-mario