[Nouveau] Nouveau Digest, Vol 131, Issue 3

[Ilia Mirkin]

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.

>> It's sending 8bpc data out to the screen, unless you're using a DP
>> monitor (and probably would need a Kepler GPU for that anyways).
>
>
> I think a long time ago i tested 10 bpc output over VGA with the proprietary
> driver on GeForce 8800, and the current readme for the NVidia blob says it
> can do 10 bpc over VGA and DisplayPort, but only dithering over DVI and
> HDMI.

I think that 10bpc HDMI support came with HDMI 1.3. Older devices (esp
Tesla era) won't support that. Intuitively seems like it should Just
Work (tm) over VGA. Not sure which DP version supported 10bpc+.

> I think i read somewhere that at least Pascal could do some deep color
> output over HDMI as well, which makes sense for HDMI-based HDR-10 support.

I believe Kepler+ devices (and perhaps GF119 as well) should support
higher bpc over HDMI. However there's no support for that in nouveau
right now. I happen to have a monitor (TV) that advertises 12bpc
support, so I may play with it.

Here's how dithering is controlled:

https://github.com/envytools/envytools/blob/master/rnndb/display/nv_evo.xml#L435

(and also exposed in the public display class docs at
http://download.nvidia.com/open-gpu-doc/Display-Class-Methods/2/ )

In theory turning off dithering should also flip off that ENABLE bit,
but perhaps we messed something up. Or HDMI is extra-special and
doesn't respect that bit and always has it enabled.

  -ilia