drm/amd/display: decouple steps for mapping CRTC degamma to DC plane

The next patch adds pre-blending degamma to AMD color mgmt pipeline, but
pre-blending degamma caps (DPP) is currently in use to provide DRM CRTC
atomic degamma or implict degamma on legacy gamma. Detach degamma usage
regarging CRTC color properties to manage plane and CRTC color
correction combinations.
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Melissa Wen <mwen@igalia.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_color.c

@@ -789,20 +789,9 @@ int amdgpu_dm_update_crtc_color_mgmt(struct dm_crtc_state *crtc)
 	return 0;
 }
 
-/**
- * amdgpu_dm_update_plane_color_mgmt: Maps DRM color management to DC plane.
- * @crtc: amdgpu_dm crtc state
- * @dc_plane_state: target DC surface
- *
- * Update the underlying dc_stream_state's input transfer function (ITF) in
- * preparation for hardware commit. The transfer function used depends on
- * the preparation done on the stream for color management.
- *
- * Returns:
- * 0 on success. -ENOMEM if mem allocation fails.
- */
-int amdgpu_dm_update_plane_color_mgmt(struct dm_crtc_state *crtc,
-				      struct dc_plane_state *dc_plane_state)
+static int
+map_crtc_degamma_to_dc_plane(struct dm_crtc_state *crtc,
+			     struct dc_plane_state *dc_plane_state)
 {
 	const struct drm_color_lut *degamma_lut;
 	enum dc_transfer_func_predefined tf = TRANSFER_FUNCTION_SRGB;
@@ -825,8 +814,7 @@ int amdgpu_dm_update_plane_color_mgmt(struct dm_crtc_state *crtc,
 						 &degamma_size);
 		ASSERT(degamma_size == MAX_COLOR_LUT_ENTRIES);
 
-		dc_plane_state->in_transfer_func->type =
-			TF_TYPE_DISTRIBUTED_POINTS;
+		dc_plane_state->in_transfer_func->type = TF_TYPE_DISTRIBUTED_POINTS;
 
 		/*
 		 * This case isn't fully correct, but also fairly
@@ -862,7 +850,7 @@ int amdgpu_dm_update_plane_color_mgmt(struct dm_crtc_state *crtc,
 				   degamma_lut, degamma_size);
 		if (r)
 			return r;
-	} else if (crtc->cm_is_degamma_srgb) {
+	} else {
 		/*
 		 * For legacy gamma support we need the regamma input
 		 * in linear space. Assume that the input is sRGB.
@@ -872,8 +860,44 @@ int amdgpu_dm_update_plane_color_mgmt(struct dm_crtc_state *crtc,
 
 		if (tf != TRANSFER_FUNCTION_SRGB &&
 		    !mod_color_calculate_degamma_params(NULL,
-			    dc_plane_state->in_transfer_func, NULL, false))
+							dc_plane_state->in_transfer_func,
+							NULL, false))
 			return -ENOMEM;
+	}
+
+	return 0;
+}
+
+/**
+ * amdgpu_dm_update_plane_color_mgmt: Maps DRM color management to DC plane.
+ * @crtc: amdgpu_dm crtc state
+ * @dc_plane_state: target DC surface
+ *
+ * Update the underlying dc_stream_state's input transfer function (ITF) in
+ * preparation for hardware commit. The transfer function used depends on
+ * the preparation done on the stream for color management.
+ *
+ * Returns:
+ * 0 on success. -ENOMEM if mem allocation fails.
+ */
+int amdgpu_dm_update_plane_color_mgmt(struct dm_crtc_state *crtc,
+				      struct dc_plane_state *dc_plane_state)
+{
+	bool has_crtc_cm_degamma;
+	int ret;
+
+	has_crtc_cm_degamma = (crtc->cm_has_degamma || crtc->cm_is_degamma_srgb);
+	if (has_crtc_cm_degamma){
+		/*
+		 * AMD HW doesn't have post-blending degamma caps. When DRM
+		 * CRTC atomic degamma is set, we maps it to DPP degamma block
+		 * (pre-blending) or, on legacy gamma, we use DPP degamma to
+		 * linearize (implicit degamma) from sRGB/BT709 according to
+		 * the input space.
+		 */
+		ret = map_crtc_degamma_to_dc_plane(crtc, dc_plane_state);
+		if (ret)
+			return ret;
 	} else {
 		/* ...Otherwise we can just bypass the DGM block. */
 		dc_plane_state->in_transfer_func->type = TF_TYPE_BYPASS;