[PATCH 5.15.y] drm/amd/display: enable cursor degamma for DCN3+ DRM legacy gamma

[Melissa Wen <mwen@igalia.com>]

For DRM legacy gamma, AMD display manager applies implicit sRGB degamma
using a pre-defined sRGB transfer function. It works fine for DCN2
family where degamma ROM and custom curves go to the same color block.
But, on DCN3+, degamma is split into two blocks: degamma ROM for
pre-defined TFs and `gamma correction` for user/custom curves and
degamma ROM settings doesn't apply to cursor plane. To get DRM legacy
gamma working as expected, enable cursor degamma ROM for implict sRGB
degamma on HW with this configuration.

Cc: stable@vger.kernel.org
Link: https://gitlab.freedesktop.org/drm/amd/-/issues/2803
Fixes: 96b020e2163f ("drm/amd/display: check attr flag before set cursor degamma on DCN3+")
Signed-off-by: Melissa Wen <mwen@igalia.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 57a943ebfcdb4a97fbb409640234bdb44bfa1953)
Signed-off-by: Melissa Wen <mwen@igalia.com>
---
 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
index 4cf33abfb7cc..dd7e0f8c3706 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -8790,6 +8790,13 @@ static void handle_cursor_update(struct drm_plane *plane,
 	attributes.rotation_angle    = 0;
 	attributes.attribute_flags.value = 0;
 
+	/* Enable cursor degamma ROM on DCN3+ for implicit sRGB degamma in DRM
+	 * legacy gamma setup.
+	 */
+	if (crtc_state->cm_is_degamma_srgb &&
+	    adev->dm.dc->caps.color.dpp.gamma_corr)
+		attributes.attribute_flags.bits.ENABLE_CURSOR_DEGAMMA = 1;
+
 	attributes.pitch = afb->base.pitches[0] / afb->base.format->cpp[0];
 
 	if (crtc_state->stream) {
-- 
2.40.1