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

[Harry Wentland <harry.wentland@amd.com>]

On 2021-07-15 3:19 p.m., Mario Kleiner wrote:
> On Thu, Jul 15, 2021 at 6:10 PM Alex Deucher <alexdeucher@gmail.com> wrote:
>>
>> On Wed, Jul 14, 2021 at 4:15 AM Liviu Dudau <liviu@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@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@144 Hz DP monitor with DCN-1, DCE-11.2, and
> a 2560x1440@100 Hz HDMI monitor iirc with DCN-1, DCE-8.3, and i think
> on a 2880x1800@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@gmail.com>

Makes sense.

Reviewed-by: Harry Wentland <harry.wentland@amd.com>

Harry

> 
> -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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