drm/amd/display: Rework CRTC color management

[Why]
To prepare for the upcoming DRM plane color management properties
we need to correct a lot of wrong behavior and assumptions made for
CRTC color management.

The documentation added by this commit in amdgpu_dm_color explains
how the HW color pipeline works and its limitations with the DRM
interface.

The current implementation does the following wrong:
- Implicit sRGB DGM when no CRTC DGM is set
- Implicit sRGB RGM when no CRTC RGM is set
- No way to specify a non-linear DGM matrix that produces correct output
- No way to specify a correct RGM when a linear DGM is used

We had workarounds for passing kms_color tests but not all of the
behavior we had wrong was covered by these tests (especially when
it comes to non-linear DGM). Testing both DGM and RGM at the same time
isn't something kms_color tests well either.

[How]
The specifics for how color management works in AMDGPU and the new
behavior can be found by reading the documentation added to
amdgpu_dm_color.c from this patch.

All of the incorrect cases from the old implementation have been
addressed for the atomic interface, but there still a few TODOs for
the legacy one.

Note: this does cause regressions for kms_color@pipe-a-ctm-* over HDMI.

The result looks correct from visual inspection but the CRC no longer
matches. For reference, the test was previously doing the following:

linear degamma -> CTM -> sRGB regamma -> RGB to YUV (709) -> ...

Now the test is doing:

linear degamma -> CTM -> linear regamma -> RGB to YUV (709) -> ...
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Sun peng Li <Sunpeng.Li@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -2878,6 +2878,7 @@ static int fill_dc_plane_attributes(struct amdgpu_device *adev,
 				    struct drm_plane_state *plane_state,
 				    struct drm_crtc_state *crtc_state)
 {
+	struct dm_crtc_state *dm_crtc_state = to_dm_crtc_state(crtc_state);
 	const struct amdgpu_framebuffer *amdgpu_fb =
 		to_amdgpu_framebuffer(plane_state->fb);
 	struct dc_scaling_info scaling_info;
@@ -2922,13 +2923,11 @@ static int fill_dc_plane_attributes(struct amdgpu_device *adev,
 	 * Always set input transfer function, since plane state is refreshed
 	 * every time.
 	 */
-	ret = amdgpu_dm_set_degamma_lut(crtc_state, dc_plane_state);
-	if (ret) {
-		dc_transfer_func_release(dc_plane_state->in_transfer_func);
-		dc_plane_state->in_transfer_func = NULL;
-	}
+	ret = amdgpu_dm_update_plane_color_mgmt(dm_crtc_state, dc_plane_state);
+	if (ret)
+		return ret;
 
-	return ret;
+	return 0;
 }
 
 static void update_stream_scaling_settings(const struct drm_display_mode *mode,
@@ -3517,6 +3516,8 @@ dm_crtc_duplicate_state(struct drm_crtc *crtc)
 	state->vrr_supported = cur->vrr_supported;
 	state->freesync_config = cur->freesync_config;
 	state->crc_enabled = cur->crc_enabled;
+	state->cm_has_degamma = cur->cm_has_degamma;
+	state->cm_is_degamma_srgb = cur->cm_is_degamma_srgb;
 
 	/* TODO Duplicate dc_stream after objects are stream object is flattened */
 
@@ -5674,8 +5675,18 @@ static void amdgpu_dm_commit_planes(struct drm_atomic_state *state,
 			bundle->stream_update.dst = acrtc_state->stream->dst;
 		}
 
-		if (new_pcrtc_state->color_mgmt_changed)
-			bundle->stream_update.out_transfer_func = acrtc_state->stream->out_transfer_func;
+		if (new_pcrtc_state->color_mgmt_changed) {
+			/*
+			 * TODO: This isn't fully correct since we've actually
+			 * already modified the stream in place.
+			 */
+			bundle->stream_update.gamut_remap =
+				&acrtc_state->stream->gamut_remap_matrix;
+			bundle->stream_update.output_csc_transform =
+				&acrtc_state->stream->csc_color_matrix;
+			bundle->stream_update.out_transfer_func =
+				acrtc_state->stream->out_transfer_func;
+		}
 
 		acrtc_state->stream->abm_level = acrtc_state->abm_level;
 		if (acrtc_state->abm_level != dm_old_crtc_state->abm_level)
@@ -6525,10 +6536,9 @@ static int dm_update_crtc_state(struct amdgpu_display_manager *dm,
 	 */
 	if (dm_new_crtc_state->base.color_mgmt_changed ||
 	    drm_atomic_crtc_needs_modeset(new_crtc_state)) {
-		ret = amdgpu_dm_set_regamma_lut(dm_new_crtc_state);
+		ret = amdgpu_dm_update_crtc_color_mgmt(dm_new_crtc_state);
 		if (ret)
 			goto fail;
-		amdgpu_dm_set_ctm(dm_new_crtc_state);
 	}
 
 	/* Update Freesync settings. */
@@ -6831,6 +6841,8 @@ dm_determine_update_type_for_commit(struct amdgpu_display_manager *dm,
 						new_dm_plane_state->dc_state->in_transfer_func;
 				stream_update.gamut_remap =
 						&new_dm_crtc_state->stream->gamut_remap_matrix;
+				stream_update.output_csc_transform =
+						&new_dm_crtc_state->stream->csc_color_matrix;
 				stream_update.out_transfer_func =
 						new_dm_crtc_state->stream->out_transfer_func;
 			}

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h

@@ -278,6 +278,9 @@ struct dm_crtc_state {
 	struct drm_crtc_state base;
 	struct dc_stream_state *stream;
 
+	bool cm_has_degamma;
+	bool cm_is_degamma_srgb;
+
 	int active_planes;
 	bool interrupts_enabled;
 
@@ -367,10 +370,9 @@ void amdgpu_dm_crtc_handle_crc_irq(struct drm_crtc *crtc);
 #define MAX_COLOR_LEGACY_LUT_ENTRIES 256
 
 void amdgpu_dm_init_color_mod(void);
-int amdgpu_dm_set_degamma_lut(struct drm_crtc_state *crtc_state,
-			      struct dc_plane_state *dc_plane_state);
-void amdgpu_dm_set_ctm(struct dm_crtc_state *crtc);
-int amdgpu_dm_set_regamma_lut(struct dm_crtc_state *crtc);
+int amdgpu_dm_update_crtc_color_mgmt(struct dm_crtc_state *crtc);
+int amdgpu_dm_update_plane_color_mgmt(struct dm_crtc_state *crtc,
+				      struct dc_plane_state *dc_plane_state);
 
 extern const struct drm_encoder_helper_funcs amdgpu_dm_encoder_helper_funcs;
 

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

@@ -27,6 +27,47 @@
 #include "amdgpu_dm.h"
 #include "dc.h"
 #include "modules/color/color_gamma.h"
+#include "basics/conversion.h"
+
+/*
+ * The DC interface to HW gives us the following color management blocks
+ * per pipe (surface):
+ *
+ * - Input gamma LUT (de-normalized)
+ * - Input CSC (normalized)
+ * - Surface degamma LUT (normalized)
+ * - Surface CSC (normalized)
+ * - Surface regamma LUT (normalized)
+ * - Output CSC (normalized)
+ *
+ * But these aren't a direct mapping to DRM color properties. The current DRM
+ * interface exposes CRTC degamma, CRTC CTM and CRTC regamma while our hardware
+ * is essentially giving:
+ *
+ * Plane CTM -> Plane degamma -> Plane CTM -> Plane regamma -> Plane CTM
+ *
+ * The input gamma LUT block isn't really applicable here since it operates
+ * on the actual input data itself rather than the HW fp representation. The
+ * input and output CSC blocks are technically available to use as part of
+ * the DC interface but are typically used internally by DC for conversions
+ * between color spaces. These could be blended together with user
+ * adjustments in the future but for now these should remain untouched.
+ *
+ * The pipe blending also happens after these blocks so we don't actually
+ * support any CRTC props with correct blending with multiple planes - but we
+ * can still support CRTC color management properties in DM in most single
+ * plane cases correctly with clever management of the DC interface in DM.
+ *
+ * As per DRM documentation, blocks should be in hardware bypass when their
+ * respective property is set to NULL. A linear DGM/RGM LUT should also
+ * considered as putting the respective block into bypass mode.
+ *
+ * This means that the following
+ * configuration is assumed to be the default:
+ *
+ * Plane DGM Bypass -> Plane CTM Bypass -> Plane RGM Bypass -> ...
+ * CRTC DGM Bypass -> CRTC CTM Bypass -> CRTC RGM Bypass
+ */
 
 #define MAX_DRM_LUT_VALUE 0xFFFF
 
@@ -41,6 +82,13 @@ void amdgpu_dm_init_color_mod(void)
 	setup_x_points_distribution();
 }
 
+/* Extracts the DRM lut and lut size from a blob. */
+static const struct drm_color_lut *
+__extract_blob_lut(const struct drm_property_blob *blob, uint32_t *size)
+{
+	*size = blob ? drm_color_lut_size(blob) : 0;
+	return blob ? (struct drm_color_lut *)blob->data : NULL;
+}
 
 /*
  * Return true if the given lut is a linear mapping of values, i.e. it acts
@@ -50,7 +98,7 @@ void amdgpu_dm_init_color_mod(void)
  * f(a) = (0xFF00/MAX_COLOR_LUT_ENTRIES-1)a; for integer a in
  *                                           [0, MAX_COLOR_LUT_ENTRIES)
  */
-static bool __is_lut_linear(struct drm_color_lut *lut, uint32_t size)
+static bool __is_lut_linear(const struct drm_color_lut *lut, uint32_t size)
 {
 	int i;
 	uint32_t expected;
@@ -75,9 +123,8 @@ static bool __is_lut_linear(struct drm_color_lut *lut, uint32_t size)
  * Convert the drm_color_lut to dc_gamma. The conversion depends on the size
  * of the lut - whether or not it's legacy.
  */
-static void __drm_lut_to_dc_gamma(struct drm_color_lut *lut,
-				  struct dc_gamma *gamma,
-				  bool is_legacy)
+static void __drm_lut_to_dc_gamma(const struct drm_color_lut *lut,
+				  struct dc_gamma *gamma, bool is_legacy)
 {
 	uint32_t r, g, b;
 	int i;
@@ -107,103 +154,16 @@ static void __drm_lut_to_dc_gamma(struct drm_color_lut *lut,
 	}
 }
 
-/**
- * amdgpu_dm_set_regamma_lut: Set regamma lut for the given CRTC.
- * @crtc: amdgpu_dm crtc state
- *
- * Update the underlying dc_stream_state's output transfer function (OTF) in
- * preparation for hardware commit. If no lut is specified by user, we default
- * to SRGB.
- *
- * RETURNS:
- * 0 on success, -ENOMEM if memory cannot be allocated to calculate the OTF.
- */
-int amdgpu_dm_set_regamma_lut(struct dm_crtc_state *crtc)
-{
-	struct drm_property_blob *blob = crtc->base.gamma_lut;
-	struct dc_stream_state *stream = crtc->stream;
-	struct amdgpu_device *adev = (struct amdgpu_device *)
-		crtc->base.state->dev->dev_private;
-	struct drm_color_lut *lut;
-	uint32_t lut_size;
-	struct dc_gamma *gamma = NULL;
-	enum dc_transfer_func_type old_type = stream->out_transfer_func->type;
-
-	bool ret;
-
-	if (!blob && adev->asic_type <= CHIP_RAVEN) {
-		/* By default, use the SRGB predefined curve.*/
-		stream->out_transfer_func->type = TF_TYPE_PREDEFINED;
-		stream->out_transfer_func->tf = TRANSFER_FUNCTION_SRGB;
-		return 0;
-	}
-
-	if (blob) {
-		lut = (struct drm_color_lut *)blob->data;
-		lut_size = blob->length / sizeof(struct drm_color_lut);
-
-		gamma = dc_create_gamma();
-		if (!gamma)
-			return -ENOMEM;
-
-		gamma->num_entries = lut_size;
-		if (gamma->num_entries == MAX_COLOR_LEGACY_LUT_ENTRIES)
-			gamma->type = GAMMA_RGB_256;
-		else if (gamma->num_entries == MAX_COLOR_LUT_ENTRIES)
-			gamma->type = GAMMA_CS_TFM_1D;
-		else {
-			/* Invalid lut size */
-			dc_gamma_release(&gamma);
-			return -EINVAL;
-		}
-
-		/* Convert drm_lut into dc_gamma */
-		__drm_lut_to_dc_gamma(lut, gamma, gamma->type == GAMMA_RGB_256);
-	}
-
-	/* predefined gamma ROM only exist for RAVEN and pre-RAVEN ASIC,
-	 * set canRomBeUsed accordingly
-	 */
-	stream->out_transfer_func->type = TF_TYPE_DISTRIBUTED_POINTS;
-	ret = mod_color_calculate_regamma_params(stream->out_transfer_func,
-			gamma, true, adev->asic_type <= CHIP_NAVI10, NULL);
-
-	if (gamma)
-		dc_gamma_release(&gamma);
-
-	if (!ret) {
-		stream->out_transfer_func->type = old_type;
-		DRM_ERROR("Out of memory when calculating regamma params\n");
-		return -ENOMEM;
-	}
-
-	return 0;
-}
-
-/**
- * amdgpu_dm_set_ctm: Set the color transform matrix for the given CRTC.
- * @crtc: amdgpu_dm crtc state
- *
- * Update the underlying dc_stream_state's gamut remap matrix in preparation
- * for hardware commit. If no matrix is specified by user, gamut remap will be
- * disabled.
+/*
+ * Converts a DRM CTM to a DC CSC float matrix.
+ * The matrix needs to be a 3x4 (12 entry) matrix.
  */
-void amdgpu_dm_set_ctm(struct dm_crtc_state *crtc)
+static void __drm_ctm_to_dc_matrix(const struct drm_color_ctm *ctm,
+				   struct fixed31_32 *matrix)
 {
-
-	struct drm_property_blob *blob = crtc->base.ctm;
-	struct dc_stream_state *stream = crtc->stream;
-	struct drm_color_ctm *ctm;
 	int64_t val;
 	int i;
 
-	if (!blob) {
-		stream->gamut_remap_matrix.enable_remap = false;
-		return;
-	}
-
-	stream->gamut_remap_matrix.enable_remap = true;
-	ctm = (struct drm_color_ctm *)blob->data;
 	/*
 	 * DRM gives a 3x3 matrix, but DC wants 3x4. Assuming we're operating
 	 * with homogeneous coordinates, augment the matrix with 0's.
@@ -215,83 +175,306 @@ void amdgpu_dm_set_ctm(struct dm_crtc_state *crtc)
 	for (i = 0; i < 12; i++) {
 		/* Skip 4th element */
 		if (i % 4 == 3) {
-			stream->gamut_remap_matrix.matrix[i] = dc_fixpt_zero;
+			matrix[i] = dc_fixpt_zero;
 			continue;
 		}
 
 		/* gamut_remap_matrix[i] = ctm[i - floor(i/4)] */
-		val = ctm->matrix[i - (i/4)];
+		val = ctm->matrix[i - (i / 4)];
 		/* If negative, convert to 2's complement. */
 		if (val & (1ULL << 63))
 			val = -(val & ~(1ULL << 63));
 
-		stream->gamut_remap_matrix.matrix[i].value = val;
+		matrix[i].value = val;
 	}
 }
 
+/* Calculates the legacy transfer function - only for sRGB input space. */
+static int __set_legacy_tf(struct dc_transfer_func *func,
+			   const struct drm_color_lut *lut, uint32_t lut_size,
+			   bool has_rom)
+{
+	struct dc_gamma *gamma = NULL;
+	bool res;
 
-/**
- * amdgpu_dm_set_degamma_lut: Set degamma lut for the given CRTC.
- * @crtc: amdgpu_dm crtc state
- *
- * Update the underlying dc_stream_state's input transfer function (ITF) in
- * preparation for hardware commit. If no lut is specified by user, we default
- * to SRGB degamma.
- *
- * We support degamma bypass, predefined SRGB, and custom degamma
- *
- * RETURNS:
- * 0 on success
- * -EINVAL if crtc_state has a degamma_lut of invalid size
- * -ENOMEM if gamma allocation fails
- */
-int amdgpu_dm_set_degamma_lut(struct drm_crtc_state *crtc_state,
-			      struct dc_plane_state *dc_plane_state)
+	ASSERT(lut && lut_size == MAX_COLOR_LEGACY_LUT_ENTRIES);
+
+	gamma = dc_create_gamma();
+	if (!gamma)
+		return -ENOMEM;
+
+	gamma->type = GAMMA_RGB_256;
+	gamma->num_entries = lut_size;
+	__drm_lut_to_dc_gamma(lut, gamma, true);
+
+	res = mod_color_calculate_regamma_params(func, gamma, true, has_rom,
+						 NULL);
+
+	return res ? 0 : -ENOMEM;
+}
+
+/* Calculates the output transfer function based on expected input space. */
+static int __set_output_tf(struct dc_transfer_func *func,
+			   const struct drm_color_lut *lut, uint32_t lut_size,
+			   bool has_rom)
 {
-	struct drm_property_blob *blob = crtc_state->degamma_lut;
-	struct drm_color_lut *lut;
-	uint32_t lut_size;
-	struct dc_gamma *gamma;
-	bool ret;
-
-	if (!blob) {
-		/* Default to SRGB */
-		dc_plane_state->in_transfer_func->type = TF_TYPE_PREDEFINED;
-		dc_plane_state->in_transfer_func->tf = TRANSFER_FUNCTION_SRGB;
-		return 0;
-	}
+	struct dc_gamma *gamma = NULL;
+	bool res;
 
-	lut = (struct drm_color_lut *)blob->data;
-	if (__is_lut_linear(lut, MAX_COLOR_LUT_ENTRIES)) {
-		dc_plane_state->in_transfer_func->type = TF_TYPE_BYPASS;
-		dc_plane_state->in_transfer_func->tf = TRANSFER_FUNCTION_LINEAR;
-		return 0;
-	}
+	ASSERT(lut && lut_size == MAX_COLOR_LUT_ENTRIES);
 
 	gamma = dc_create_gamma();
 	if (!gamma)
 		return -ENOMEM;
 
-	lut_size = blob->length / sizeof(struct drm_color_lut);
 	gamma->num_entries = lut_size;
-	if (gamma->num_entries == MAX_COLOR_LUT_ENTRIES)
+	__drm_lut_to_dc_gamma(lut, gamma, false);
+
+	if (func->tf == TRANSFER_FUNCTION_LINEAR) {
+		/*
+		 * Color module doesn't like calculating regamma params
+		 * on top of a linear input. But degamma params can be used
+		 * instead to simulate this.
+		 */
 		gamma->type = GAMMA_CUSTOM;
-	else {
-		dc_gamma_release(&gamma);
-		return -EINVAL;
+		res = mod_color_calculate_degamma_params(func, gamma, true);
+	} else {
+		/*
+		 * Assume sRGB. The actual mapping will depend on whether the
+		 * input was legacy or not.
+		 */
+		gamma->type = GAMMA_CS_TFM_1D;
+		res = mod_color_calculate_regamma_params(func, gamma, false,
+							 has_rom, NULL);
 	}
 
+	dc_gamma_release(&gamma);
+
+	return res ? 0 : -ENOMEM;
+}
+
+/* Caculates the input transfer function based on expected input space. */
+static int __set_input_tf(struct dc_transfer_func *func,
+			  const struct drm_color_lut *lut, uint32_t lut_size)
+{
+	struct dc_gamma *gamma = NULL;
+	bool res;
+
+	gamma = dc_create_gamma();
+	if (!gamma)
+		return -ENOMEM;
+
+	gamma->type = GAMMA_CUSTOM;
+	gamma->num_entries = lut_size;
+
 	__drm_lut_to_dc_gamma(lut, gamma, false);
 
-	dc_plane_state->in_transfer_func->type = TF_TYPE_DISTRIBUTED_POINTS;
-	ret = mod_color_calculate_degamma_params(dc_plane_state->in_transfer_func, gamma, true);
+	res = mod_color_calculate_degamma_params(func, gamma, true);
 	dc_gamma_release(&gamma);
-	if (!ret) {
-		dc_plane_state->in_transfer_func->type = TF_TYPE_BYPASS;
-		DRM_ERROR("Out of memory when calculating degamma params\n");
-		return -ENOMEM;
+
+	return res ? 0 : -ENOMEM;
+}
+
+/**
+ * amdgpu_dm_update_crtc_color_mgmt: Maps DRM color management to DC stream.
+ * @crtc: amdgpu_dm crtc state
+ *
+ * With no plane level color management properties we're free to use any
+ * of the HW blocks as long as the CRTC CTM always comes before the
+ * CRTC RGM and after the CRTC DGM.
+ *
+ * The CRTC RGM block will be placed in the RGM LUT block if it is non-linear.
+ * The CRTC DGM block will be placed in the DGM LUT block if it is non-linear.
+ * The CRTC CTM will be placed in the gamut remap block if it is non-linear.
+ *
+ * The RGM block is typically more fully featured and accurate across
+ * all ASICs - DCE can't support a custom non-linear CRTC DGM.
+ *
+ * For supporting both plane level color management and CRTC level color
+ * management at once we have to either restrict the usage of CRTC properties
+ * or blend adjustments together.
+ *
+ * Returns 0 on success.
+ */
+int amdgpu_dm_update_crtc_color_mgmt(struct dm_crtc_state *crtc)
+{
+	struct dc_stream_state *stream = crtc->stream;
+	struct amdgpu_device *adev =
+		(struct amdgpu_device *)crtc->base.state->dev->dev_private;
+	bool has_rom = adev->asic_type <= CHIP_RAVEN;
+	struct drm_color_ctm *ctm = NULL;
+	const struct drm_color_lut *degamma_lut, *regamma_lut;
+	uint32_t degamma_size, regamma_size;
+	bool has_regamma, has_degamma;
+	bool is_legacy;
+	int r;
+
+	degamma_lut = __extract_blob_lut(crtc->base.degamma_lut, &degamma_size);
+	if (degamma_lut && degamma_size != MAX_COLOR_LUT_ENTRIES)
+		return -EINVAL;
+
+	regamma_lut = __extract_blob_lut(crtc->base.gamma_lut, &regamma_size);
+	if (regamma_lut && regamma_size != MAX_COLOR_LUT_ENTRIES &&
+	    regamma_size != MAX_COLOR_LEGACY_LUT_ENTRIES)
+		return -EINVAL;
+
+	has_degamma =
+		degamma_lut && !__is_lut_linear(degamma_lut, degamma_size);
+
+	has_regamma =
+		regamma_lut && !__is_lut_linear(regamma_lut, regamma_size);
+
+	is_legacy = regamma_size == MAX_COLOR_LEGACY_LUT_ENTRIES;
+
+	/* Reset all adjustments. */
+	crtc->cm_has_degamma = false;
+	crtc->cm_is_degamma_srgb = false;
+
+	/* Setup regamma and degamma. */
+	if (is_legacy) {
+		/*
+		 * Legacy regamma forces us to use the sRGB RGM as a base.
+		 * This also means we can't use linear DGM since DGM needs
+		 * to use sRGB as a base as well, resulting in incorrect CRTC
+		 * DGM and CRTC CTM.
+		 *
+		 * TODO: Just map this to the standard regamma interface
+		 * instead since this isn't really right. One of the cases
+		 * where this setup currently fails is trying to do an
+		 * inverse color ramp in legacy userspace.
+		 */
+		crtc->cm_is_degamma_srgb = true;
+		stream->out_transfer_func->type = TF_TYPE_DISTRIBUTED_POINTS;
+		stream->out_transfer_func->tf = TRANSFER_FUNCTION_SRGB;
+
+		r = __set_legacy_tf(stream->out_transfer_func, regamma_lut,
+				    regamma_size, has_rom);
+		if (r)
+			return r;
+	} else if (has_regamma) {
+		/* CRTC RGM goes into RGM LUT. */
+		stream->out_transfer_func->type = TF_TYPE_DISTRIBUTED_POINTS;
+		stream->out_transfer_func->tf = TRANSFER_FUNCTION_LINEAR;
+
+		r = __set_output_tf(stream->out_transfer_func, regamma_lut,
+				    regamma_size, has_rom);
+		if (r)
+			return r;
+	} else {
+		/*
+		 * No CRTC RGM means we can just put the block into bypass
+		 * since we don't have any plane level adjustments using it.
+		 */
+		stream->out_transfer_func->type = TF_TYPE_BYPASS;
+		stream->out_transfer_func->tf = TRANSFER_FUNCTION_LINEAR;
+	}
+
+	/*
+	 * CRTC DGM goes into DGM LUT. It would be nice to place it
+	 * into the RGM since it's a more featured block but we'd
+	 * have to place the CTM in the OCSC in that case.
+	 */
+	crtc->cm_has_degamma = has_degamma;
+
+	/* Setup CRTC CTM. */
+	if (crtc->base.ctm) {
+		ctm = (struct drm_color_ctm *)crtc->base.ctm->data;
+
+		/*
+		 * Gamut remapping must be used for gamma correction
+		 * since it comes before the regamma correction.
+		 *
+		 * OCSC could be used for gamma correction, but we'd need to
+		 * blend the adjustments together with the required output
+		 * conversion matrix - so just use the gamut remap block
+		 * for now.
+		 */
+		__drm_ctm_to_dc_matrix(ctm, stream->gamut_remap_matrix.matrix);
+
+		stream->gamut_remap_matrix.enable_remap = true;
+		stream->csc_color_matrix.enable_adjustment = false;
+	} else {
+		/* Bypass CTM. */
+		stream->gamut_remap_matrix.enable_remap = false;
+		stream->csc_color_matrix.enable_adjustment = false;
 	}
 
 	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 prepartion done on the stream for color management.
+ *
+ * Returns 0 on success.
+ */
+int amdgpu_dm_update_plane_color_mgmt(struct dm_crtc_state *crtc,
+				      struct dc_plane_state *dc_plane_state)
+{
+	const struct drm_color_lut *degamma_lut;
+	uint32_t degamma_size;
+	int r;
+
+	if (crtc->cm_has_degamma) {
+		degamma_lut = __extract_blob_lut(crtc->base.degamma_lut,
+						 &degamma_size);
+		ASSERT(degamma_size == MAX_COLOR_LUT_ENTRIES);
+
+		dc_plane_state->in_transfer_func->type =
+			TF_TYPE_DISTRIBUTED_POINTS;
+
+		/*
+		 * This case isn't fully correct, but also fairly
+		 * uncommon. This is userspace trying to use a
+		 * legacy gamma LUT + atomic degamma LUT
+		 * at the same time.
+		 *
+		 * Legacy gamma requires the input to be in linear
+		 * space, so that means we need to apply an sRGB
+		 * degamma. But color module also doesn't support
+		 * a user ramp in this case so the degamma will
+		 * be lost.
+		 *
+		 * Even if we did support it, it's still not right:
+		 *
+		 * Input -> CRTC DGM -> sRGB DGM -> CRTC CTM ->
+		 * sRGB RGM -> CRTC RGM -> Output
+		 *
+		 * The CSC will be done in the wrong space since
+		 * we're applying an sRGB DGM on top of the CRTC
+		 * DGM.
+		 *
+		 * TODO: Don't use the legacy gamma interface and just
+		 * map these to the atomic one instead.
+		 */
+		if (crtc->cm_is_degamma_srgb)
+			dc_plane_state->in_transfer_func->tf =
+				TRANSFER_FUNCTION_SRGB;
+		else
+			dc_plane_state->in_transfer_func->tf =
+				TRANSFER_FUNCTION_LINEAR;
+
+		r = __set_input_tf(dc_plane_state->in_transfer_func,
+				   degamma_lut, degamma_size);
+		if (r)
+			return r;
+	} else if (crtc->cm_is_degamma_srgb) {
+		/*
+		 * For legacy gamma support we need the regamma input
+		 * in linear space. Assume that the input is sRGB.
+		 */
+		dc_plane_state->in_transfer_func->type = TF_TYPE_PREDEFINED;
+		dc_plane_state->in_transfer_func->tf = TRANSFER_FUNCTION_SRGB;
+	} else {
+		/* ...Otherwise we can just bypass the DGM block. */
+		dc_plane_state->in_transfer_func->type = TF_TYPE_BYPASS;
+		dc_plane_state->in_transfer_func->tf = TRANSFER_FUNCTION_LINEAR;
+	}
+
+	return 0;
+}