On 03/03/2018 12:59 AM, Ilia Mirkin wrote:
On Fri, Mar 2, 2018 at 6:46 PM, Mario Kleiner
<mario.kleiner...@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.
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
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