From: James Lin <[email protected]> [why] On DCN 4.2 the global alpha is reported using 12 bits (MPCC_GLOBAL_ALPHA spans bits [0:11]), whereas other ASICs such as DCN 3.1.4 use an 8-bit field (MPCC_GLOBAL_ALPHA spans bits [16:23]). The DRM plane alpha property is 16-bit and amdgpu_dm unconditionally scaled it down by >> 8, which only matches the 8-bit hardware field. On DCN 4.2 this fed a value that was 4 bits too small into the 12-bit field, so the hardware applied the wrong global alpha and the resulting blended output did not match the expected hw * alpha value.
[how] Detect DCN 4.2 via amdgpu_ip_version(adev, DCE_HWIP, 0) and scale the 16-bit plane alpha by >> 4 to fill the 12-bit MPCC_GLOBAL_ALPHA field. All other ASICs keep the existing >> 8 behavior for their 8-bit field. Reviewed-by: ChiaHsuan (Tom) Chung <[email protected]> Signed-off-by: James Lin <[email protected]> Signed-off-by: George Zhang <[email protected]> --- .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_plane.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_plane.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_plane.c index 20bac36be335..458b3dcdbfa3 100644 --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_plane.c +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_plane.c @@ -137,8 +137,18 @@ void amdgpu_dm_plane_fill_blending_from_plane_state(const struct drm_plane_state } if (plane_state->alpha < 0xffff) { + struct amdgpu_device *adev = drm_to_adev(plane_state->plane->dev); *global_alpha = true; - *global_alpha_value = plane_state->alpha >> 8; + /* + * DCN 4.2 uses a 12-bit MPCC_GLOBAL_ALPHA field, while + * other ASICs use an 8-bit field. The DRM plane alpha is + * 16-bit, so scale it down to the width the hardware expects. + */ + if (amdgpu_ip_version(adev, DCE_HWIP, 0) == IP_VERSION(4, 2, 0)) + *global_alpha_value = plane_state->alpha >> 4; + else + *global_alpha_value = plane_state->alpha >> 8; + } } EXPORT_IF_KUNIT(amdgpu_dm_plane_fill_blending_from_plane_state); -- 2.53.0
