[PATCH 1/2] drm/amd/display: Introduce overlay cursor mode

[Pekka Paalanen]

On Fri, 15 Mar 2024 13:09:57 -0400
<sunpeng.li at amd.com> wrote:

> From: Leo Li <sunpeng.li at amd.com>
> 
> [Why]
> 
> DCN is the display hardware for amdgpu. DRM planes are backed by DCN
> hardware pipes, which carry pixel data from one end (memory), to the
> other (output encoder).
> 
> Each DCN pipe has the ability to blend in a cursor early on in the
> pipeline. In other words, there are no dedicated cursor planes in DCN,
> which makes cursor behavior somewhat unintuitive for compositors.
> 
> For example, if the cursor is in RGB format, but the top-most DRM plane
> is in YUV format, DCN will not be able to blend them. Because of this,
> amdgpu_dm rejects all configurations where a cursor needs to be enabled
> on top of a YUV formatted plane.
> 
> From a compositor's perspective, when computing an allocation for
> hardware plane offloading, this cursor-on-yuv configuration result in an
> atomic test failure. Since the failure reason is not obvious at all,
> compositors will likely fall back to full rendering, which is not ideal.
> 
> Instead, amdgpu_dm can try to accommodate the cursor-on-yuv
> configuration by opportunistically reserving a separate DCN pipe just
> for the cursor. We can refer to this as "overlay cursor mode". It is
> contrasted with "native cursor mode", where the native DCN per-pipe
> cursor is used.

I can't comment on the code, but this explanation sounds like a really
good move!


Thanks,
pq

> [How]
> 
> On each crtc, compute whether the cursor plane should be enabled in
> overlay mode (which currently, is iff the immediate plane below has a
> YUV format). If it is, mark the CRTC as requesting overlay cursor mode.
> 
> During DC validation, attempt to enable a separate DCN pipe for the
> cursor if it's in overlay mode. If that fails, or if no overlay mode is
> requested, then fallback to native mode.
> 
> Signed-off-by: Leo Li <sunpeng.li at amd.com>
> ---
>  .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 309 +++++++++++++++---
>  .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h |   7 +
>  .../amd/display/amdgpu_dm/amdgpu_dm_crtc.c    |   1 +
>  .../amd/display/amdgpu_dm/amdgpu_dm_plane.c   |  13 +-
>  4 files changed, 288 insertions(+), 42 deletions(-)
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