drm/i915/display: Prevent double YUV range correction on HDR planes

Prevent the ICL HDR plane pipeline from performing YUV color range
correction twice when the input is in limited range. This is done by
removing the limited-range code from icl_program_input_csc().

Before this patch the following could happen: user space gives us a YUV
buffer in limited range; per the pipeline in [1], the plane would first
go through a "YUV Range correct" stage that expands the range; the plane
would then go through the "Input CSC" stage which would also expand the
range because icl_program_input_csc() would use a matrix and an offset
that assume limited-range input; this would ultimately cause dark and
light colors to appear darker and lighter than they should respectively.

This is an issue because if a buffer switches between being scanned out
and being composited with the GPU, the user will see a color difference.
If this switching happens quickly and frequently, the user will perceive
this as a flickering.

[1] https://01.org/sites/default/files/documentation/intel-gfx-prm-osrc-icllp-vol12-displayengine_0.pdf#page=281

Cc: stable@vger.kernel.org
Signed-off-by: Andres Calderon Jaramillo <andrescj@chromium.org>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201215224219.3896256-1-andrescj@google.com

drivers/gpu/drm/i915/display/intel_display.c

@@ -3584,6 +3584,8 @@ u32 glk_plane_color_ctl(const struct intel_crtc_state *crtc_state,
 			plane_color_ctl |= PLANE_COLOR_YUV_RANGE_CORRECTION_DISABLE;
 	} else if (fb->format->is_yuv) {
 		plane_color_ctl |= PLANE_COLOR_INPUT_CSC_ENABLE;
+		if (plane_state->hw.color_range == DRM_COLOR_YCBCR_FULL_RANGE)
+			plane_color_ctl |= PLANE_COLOR_YUV_RANGE_CORRECTION_DISABLE;
 	}
 
 	return plane_color_ctl;

drivers/gpu/drm/i915/display/intel_sprite.c

@@ -649,13 +649,19 @@ skl_program_scaler(struct intel_plane *plane,
 
 /* Preoffset values for YUV to RGB Conversion */
 #define PREOFF_YUV_TO_RGB_HI		0x1800
-#define PREOFF_YUV_TO_RGB_ME		0x1F00
+#define PREOFF_YUV_TO_RGB_ME		0x0000
 #define PREOFF_YUV_TO_RGB_LO		0x1800
 
 #define  ROFF(x)          (((x) & 0xffff) << 16)
 #define  GOFF(x)          (((x) & 0xffff) << 0)
 #define  BOFF(x)          (((x) & 0xffff) << 16)
 
+/*
+ * Programs the input color space conversion stage for ICL HDR planes.
+ * Note that it is assumed that this stage always happens after YUV
+ * range correction. Thus, the input to this stage is assumed to be
+ * in full-range YCbCr.
+ */
 static void
 icl_program_input_csc(struct intel_plane *plane,
 		      const struct intel_crtc_state *crtc_state,
@@ -703,52 +709,7 @@ icl_program_input_csc(struct intel_plane *plane,
 			0x0, 0x7800, 0x7F10,
 		},
 	};
-
-	/* Matrix for Limited Range to Full Range Conversion */
-	static const u16 input_csc_matrix_lr[][9] = {
-		/*
-		 * BT.601 Limted range YCbCr -> full range RGB
-		 * The matrix required is :
-		 * [1.164384, 0.000, 1.596027,
-		 *  1.164384, -0.39175, -0.812813,
-		 *  1.164384, 2.017232, 0.0000]
-		 */
-		[DRM_COLOR_YCBCR_BT601] = {
-			0x7CC8, 0x7950, 0x0,
-			0x8D00, 0x7950, 0x9C88,
-			0x0, 0x7950, 0x6810,
-		},
-		/*
-		 * BT.709 Limited range YCbCr -> full range RGB
-		 * The matrix required is :
-		 * [1.164384, 0.000, 1.792741,
-		 *  1.164384, -0.213249, -0.532909,
-		 *  1.164384, 2.112402, 0.0000]
-		 */
-		[DRM_COLOR_YCBCR_BT709] = {
-			0x7E58, 0x7950, 0x0,
-			0x8888, 0x7950, 0xADA8,
-			0x0, 0x7950,  0x6870,
-		},
-		/*
-		 * BT.2020 Limited range YCbCr -> full range RGB
-		 * The matrix required is :
-		 * [1.164, 0.000, 1.678,
-		 *  1.164, -0.1873, -0.6504,
-		 *  1.164, 2.1417, 0.0000]
-		 */
-		[DRM_COLOR_YCBCR_BT2020] = {
-			0x7D70, 0x7950, 0x0,
-			0x8A68, 0x7950, 0xAC00,
-			0x0, 0x7950, 0x6890,
-		},
-	};
-	const u16 *csc;
-
-	if (plane_state->hw.color_range == DRM_COLOR_YCBCR_FULL_RANGE)
-		csc = input_csc_matrix[plane_state->hw.color_encoding];
-	else
-		csc = input_csc_matrix_lr[plane_state->hw.color_encoding];
+	const u16 *csc = input_csc_matrix[plane_state->hw.color_encoding];
 
 	intel_de_write_fw(dev_priv, PLANE_INPUT_CSC_COEFF(pipe, plane_id, 0),
 			  ROFF(csc[0]) | GOFF(csc[1]));
@@ -765,14 +726,8 @@ icl_program_input_csc(struct intel_plane *plane,
 
 	intel_de_write_fw(dev_priv, PLANE_INPUT_CSC_PREOFF(pipe, plane_id, 0),
 			  PREOFF_YUV_TO_RGB_HI);
-	if (plane_state->hw.color_range == DRM_COLOR_YCBCR_FULL_RANGE)
-		intel_de_write_fw(dev_priv,
-				  PLANE_INPUT_CSC_PREOFF(pipe, plane_id, 1),
-				  0);
-	else
-		intel_de_write_fw(dev_priv,
-				  PLANE_INPUT_CSC_PREOFF(pipe, plane_id, 1),
-				  PREOFF_YUV_TO_RGB_ME);
+	intel_de_write_fw(dev_priv, PLANE_INPUT_CSC_PREOFF(pipe, plane_id, 1),
+			  PREOFF_YUV_TO_RGB_ME);
 	intel_de_write_fw(dev_priv, PLANE_INPUT_CSC_PREOFF(pipe, plane_id, 2),
 			  PREOFF_YUV_TO_RGB_LO);
 	intel_de_write_fw(dev_priv,