[PATCH] drm/vc4: Enable limited range RGB output on HDMI with CEA modes.

[Eric Anholt]

Fixes broken grayscale ramps on many HDMI monitors, where large areas
at the ends of the ramp would all appear as black or white.

Signed-off-by: Eric Anholt <eric at anholt.net>
---
 drivers/gpu/drm/vc4/vc4_hdmi.c | 31 +++++++++++++++++++++++++++++--
 drivers/gpu/drm/vc4/vc4_regs.h |  9 ++++++++-
 2 files changed, 37 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
index 9f85a579da74..1e61931846d3 100644
--- a/drivers/gpu/drm/vc4/vc4_hdmi.c
+++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
@@ -301,6 +301,7 @@ static void vc4_hdmi_encoder_mode_set(struct drm_encoder *encoder,
 				      struct drm_display_mode *unadjusted_mode,
 				      struct drm_display_mode *mode)
 {
+	struct vc4_hdmi_encoder *vc4_encoder = to_vc4_hdmi_encoder(encoder);
 	struct drm_device *dev = encoder->dev;
 	struct vc4_dev *vc4 = to_vc4_dev(dev);
 	bool debug_dump_regs = false;
@@ -316,6 +317,7 @@ static void vc4_hdmi_encoder_mode_set(struct drm_encoder *encoder,
 	u32 vertb = (VC4_SET_FIELD(0, VC4_HDMI_VERTB_VSPO) |
 		     VC4_SET_FIELD(mode->vtotal - mode->vsync_end,
 				   VC4_HDMI_VERTB_VBP));
+	u32 csc_ctl;
 
 	if (debug_dump_regs) {
 		DRM_INFO("HDMI regs before:\n");
@@ -354,9 +356,34 @@ static void vc4_hdmi_encoder_mode_set(struct drm_encoder *encoder,
 		 (vsync_pos ? 0 : VC4_HD_VID_CTL_VSYNC_LOW) |
 		 (hsync_pos ? 0 : VC4_HD_VID_CTL_HSYNC_LOW));
 
+	csc_ctl = VC4_SET_FIELD(VC4_HD_CSC_CTL_ORDER_BGR,
+				VC4_HD_CSC_CTL_ORDER);
+
+	if (vc4_encoder->hdmi_monitor && drm_match_cea_mode(mode) > 1) {
+		/* CEA VICs other than #1 requre limited range RGB
+		 * output.  Apply a colorspace conversion to squash
+		 * 0-255 down to 16-235.  The matrix here is:
+		 *
+		 * [ 0      0      0.8594 16]
+		 * [ 0      0.8594 0      16]
+		 * [ 0.8594 0      0      16]
+		 * [ 0      0      0       1]
+		 */
+		csc_ctl |= VC4_HD_CSC_CTL_ENABLE;
+		csc_ctl |= VC4_HD_CSC_CTL_RGB2YCC;
+		csc_ctl |= VC4_SET_FIELD(VC4_HD_CSC_CTL_MODE_CUSTOM,
+					 VC4_HD_CSC_CTL_MODE);
+
+		HD_WRITE(VC4_HD_CSC_12_11, (0x000 << 16) | 0x000);
+		HD_WRITE(VC4_HD_CSC_14_13, (0x100 << 16) | 0x6e0);
+		HD_WRITE(VC4_HD_CSC_22_21, (0x6e0 << 16) | 0x000);
+		HD_WRITE(VC4_HD_CSC_24_23, (0x100 << 16) | 0x000);
+		HD_WRITE(VC4_HD_CSC_32_31, (0x000 << 16) | 0x6e0);
+		HD_WRITE(VC4_HD_CSC_34_33, (0x100 << 16) | 0x000);
+	}
+
 	/* The RGB order applies even when CSC is disabled. */
-	HD_WRITE(VC4_HD_CSC_CTL, VC4_SET_FIELD(VC4_HD_CSC_CTL_ORDER_BGR,
-					       VC4_HD_CSC_CTL_ORDER));
+	HD_WRITE(VC4_HD_CSC_CTL, csc_ctl);
 
 	HDMI_WRITE(VC4_HDMI_FIFO_CTL, VC4_HDMI_FIFO_CTL_MASTER_SLAVE_N);
 
diff --git a/drivers/gpu/drm/vc4/vc4_regs.h b/drivers/gpu/drm/vc4/vc4_regs.h
index 160942a9180e..9ecd6ff3d493 100644
--- a/drivers/gpu/drm/vc4/vc4_regs.h
+++ b/drivers/gpu/drm/vc4/vc4_regs.h
@@ -528,10 +528,17 @@
 # define VC4_HD_CSC_CTL_MODE_SHIFT		2
 # define VC4_HD_CSC_CTL_MODE_RGB_TO_SD_YPRPB	0
 # define VC4_HD_CSC_CTL_MODE_RGB_TO_HD_YPRPB	1
-# define VC4_HD_CSC_CTL_MODE_CUSTOM		2
+# define VC4_HD_CSC_CTL_MODE_CUSTOM		3
 # define VC4_HD_CSC_CTL_RGB2YCC			BIT(1)
 # define VC4_HD_CSC_CTL_ENABLE			BIT(0)
 
+#define VC4_HD_CSC_12_11			0x044
+#define VC4_HD_CSC_14_13			0x048
+#define VC4_HD_CSC_22_21			0x04c
+#define VC4_HD_CSC_24_23			0x050
+#define VC4_HD_CSC_32_31			0x054
+#define VC4_HD_CSC_34_33			0x058
+
 #define VC4_HD_FRAME_COUNT			0x068
 
 /* HVS display list information. */
-- 
2.9.3