[PATCH] drm/amd/display: Fix 10bit 4K display on CIK GPUs

[Mario Kleiner]

On Thu, Jul 15, 2021 at 6:10 PM Alex Deucher <alexdeucher at gmail.com> wrote:
>
> On Wed, Jul 14, 2021 at 4:15 AM Liviu Dudau <liviu at dudau.co.uk> wrote:
> >
> > Commit 72a7cf0aec0c ("drm/amd/display: Keep linebuffer pixel depth at
> > 30bpp for DCE-11.0.") doesn't seems to have fixed 10bit 4K rendering over
> > DisplayPort for CIK GPUs. On my machine with a HAWAII GPU I get a broken
> > image that looks like it has an effective resolution of 1920x1080 but
> > scaled up in an irregular way. Reverting the commit or applying this
> > patch fixes the problem on v5.14-rc1.
> >
> > Fixes: 72a7cf0aec0c ("drm/amd/display: Keep linebuffer pixel depth at 30bpp for DCE-11.0.")
> > Signed-off-by: Liviu Dudau <liviu at dudau.co.uk>
>
> Harry or Mario any ideas?  Maybe we need finer grained DCE version
> checking?  I don't remember all of the caveats of this stuff.  DCE11
> and older is getting to be pretty old at this point.  I can just apply
> this if you don't have any insights.
>
> Alex
>

Hi Alex

I'd be fine with applying this. As my original commit says, photometer
measurements showed that increasing the line buffer depth was only
needed for my DCN-1 RavenRidge, not for my DCE-11.2 Polaris11 or a
DCE-8.3 cik, so this should probably not cause harm to the increased
precision modes.

Note that given the hardware and USB-C/DP-HDMI adapters i have, I only
tested this on a 2560x1440 at 144 Hz DP monitor with DCN-1, DCE-11.2, and
a 2560x1440 at 100 Hz HDMI monitor iirc with DCN-1, DCE-8.3, and i think
on a 2880x1800 at 60 Hz MBP Retina eDP panel with DCE-11.2. These are the
highest resolution/framerate monitors I have atm.I don't have access
to any 4k monitors, so maybe the problem is somehow specific to such
high resolutions? Maybe somewhere else in the code something would
need to be adapted? Lacking actual hw docs, my coding here is by
pattern matching against existing DC code, guessing and testing on my
limited hw samples.

Acked-by: Mario Kleiner <mario.kleiner.de at gmail.com>

-mario

> > ---
> >  drivers/gpu/drm/amd/display/dc/core/dc_resource.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/amd/display/dc/core/dc_resource.c b/drivers/gpu/drm/amd/display/dc/core/dc_resource.c
> > index a6a67244a322e..1596f6b7fed7c 100644
> > --- a/drivers/gpu/drm/amd/display/dc/core/dc_resource.c
> > +++ b/drivers/gpu/drm/amd/display/dc/core/dc_resource.c
> > @@ -1062,7 +1062,7 @@ bool resource_build_scaling_params(struct pipe_ctx *pipe_ctx)
> >          * so use only 30 bpp on DCE_VERSION_11_0. Testing with DCE 11.2 and 8.3
> >          * did not show such problems, so this seems to be the exception.
> >          */
> > -       if (plane_state->ctx->dce_version != DCE_VERSION_11_0)
> > +       if (plane_state->ctx->dce_version > DCE_VERSION_11_0)
> >                 pipe_ctx->plane_res.scl_data.lb_params.depth = LB_PIXEL_DEPTH_36BPP;
> >         else
> >                 pipe_ctx->plane_res.scl_data.lb_params.depth = LB_PIXEL_DEPTH_30BPP;
> > --
> > 2.32.0
> >
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