drm/stm: ltdc: add YCbCr 422 output support

LTDC 40100 hw version supports the YCbCr 422 output,
reducing the output pins from 24 to 16. This feature
is useful for some external devices like HDMI bridges.

Both ITU-R BT.601 & ITU-R BT.709 are supported.

It is also possible to choose the chrominance order between
* Cb is output first (Y0Cb, then Y1Cr, Y2Cb and so on).
* Cr is output first (Y0Cr, then Y1Cb, Y2Cr and so on).
Signed-off-by: Yannick Fertre <yannick.fertre@foss.st.com>
Acked-by: Philippe Cornu <philippe.cornu@foss.st.com>
Reviewed-by: Philippe Cornu <philippe.cornu@foss.st.com>
Reviewed-by: Raphael Gallais-Pou <raphael.gallais-pou@foss.st.com>
Signed-off-by: Philippe Cornu <philippe.cornu@foss.st.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211215214750.20105-1-yannick.fertre@foss.st.com

drivers/gpu/drm/stm/ltdc.c

@@ -76,6 +76,7 @@
 #define LTDC_LIPCR	0x0040		/* Line Interrupt Position Conf. */
 #define LTDC_CPSR	0x0044		/* Current Position Status */
 #define LTDC_CDSR	0x0048		/* Current Display Status */
+#define LTDC_EDCR	0x0060		/* External Display Control */
 #define LTDC_FUT	0x0090		/* Fifo underrun Threshold */
 
 /* Layer register offsets */
@@ -170,6 +171,10 @@
 #define ISR_TERRIF	BIT(2)		/* Transfer ERRor Interrupt Flag */
 #define ISR_RRIF	BIT(3)		/* Register Reload Interrupt Flag */
 
+#define EDCR_OCYEN	BIT(25)		/* Output Conversion to YCbCr 422: ENable */
+#define EDCR_OCYSEL	BIT(26)		/* Output Conversion to YCbCr 422: SELection of the CCIR */
+#define EDCR_OCYCO	BIT(27)		/* Output Conversion to YCbCr 422: Chrominance Order */
+
 #define LXCR_LEN	BIT(0)		/* Layer ENable */
 #define LXCR_COLKEN	BIT(1)		/* Color Keying Enable */
 #define LXCR_CLUTEN	BIT(4)		/* Color Look-Up Table ENable */
@@ -625,6 +630,7 @@ static void ltdc_crtc_mode_set_nofb(struct drm_crtc *crtc)
 	struct drm_display_mode *mode = &crtc->state->adjusted_mode;
 	u32 hsync, vsync, accum_hbp, accum_vbp, accum_act_w, accum_act_h;
 	u32 total_width, total_height;
+	u32 bus_formats = MEDIA_BUS_FMT_RGB888_1X24;
 	u32 bus_flags = 0;
 	u32 val;
 	int ret;
@@ -650,8 +656,11 @@ static void ltdc_crtc_mode_set_nofb(struct drm_crtc *crtc)
 
 	if (bridge && bridge->timings)
 		bus_flags = bridge->timings->input_bus_flags;
-	else if (connector)
+	else if (connector) {
 		bus_flags = connector->display_info.bus_flags;
+		if (connector->display_info.num_bus_formats)
+			bus_formats = connector->display_info.bus_formats[0];
+	}
 
 	if (!pm_runtime_active(ddev->dev)) {
 		ret = pm_runtime_get_sync(ddev->dev);
@@ -716,6 +725,36 @@ static void ltdc_crtc_mode_set_nofb(struct drm_crtc *crtc)
 	regmap_update_bits(ldev->regmap, LTDC_TWCR, TWCR_TOTALH | TWCR_TOTALW, val);
 
 	regmap_write(ldev->regmap, LTDC_LIPCR, (accum_act_h + 1));
+
+	/* Configure the output format (hw version dependent) */
+	if (ldev->caps.ycbcr_output) {
+		/* Input video dynamic_range & colorimetry */
+		int vic = drm_match_cea_mode(mode);
+		u32 val;
+
+		if (vic == 6 || vic == 7 || vic == 21 || vic == 22 ||
+		    vic == 2 || vic == 3 || vic == 17 || vic == 18)
+			/* ITU-R BT.601 */
+			val = 0;
+		else
+			/* ITU-R BT.709 */
+			val = EDCR_OCYSEL;
+
+		switch (bus_formats) {
+		case MEDIA_BUS_FMT_YUYV8_1X16:
+			/* enable ycbcr output converter */
+			regmap_write(ldev->regmap, LTDC_EDCR, EDCR_OCYEN | val);
+			break;
+		case MEDIA_BUS_FMT_YVYU8_1X16:
+			/* enable ycbcr output converter & invert chrominance order */
+			regmap_write(ldev->regmap, LTDC_EDCR, EDCR_OCYEN | EDCR_OCYCO | val);
+			break;
+		default:
+			/* disable ycbcr output converter */
+			regmap_write(ldev->regmap, LTDC_EDCR, 0);
+			break;
+		}
+	}
 }
 
 static void ltdc_crtc_atomic_flush(struct drm_crtc *crtc,
@@ -1267,6 +1306,7 @@ static int ltdc_get_caps(struct drm_device *ddev)
 		if (ldev->caps.hw_version == HWVER_10200)
 			ldev->caps.pad_max_freq_hz = 65000000;
 		ldev->caps.nb_irq = 2;
+		ldev->caps.ycbcr_output = false;
 		break;
 	case HWVER_20101:
 		ldev->caps.layer_ofs = LAY_OFS_0;
@@ -1275,6 +1315,7 @@ static int ltdc_get_caps(struct drm_device *ddev)
 		ldev->caps.non_alpha_only_l1 = false;
 		ldev->caps.pad_max_freq_hz = 150000000;
 		ldev->caps.nb_irq = 4;
+		ldev->caps.ycbcr_output = false;
 		break;
 	case HWVER_40100:
 		ldev->caps.layer_ofs = LAY_OFS_1;
@@ -1283,6 +1324,7 @@ static int ltdc_get_caps(struct drm_device *ddev)
 		ldev->caps.non_alpha_only_l1 = false;
 		ldev->caps.pad_max_freq_hz = 90000000;
 		ldev->caps.nb_irq = 2;
+		ldev->caps.ycbcr_output = true;
 		break;
 	default:
 		return -ENODEV;

drivers/gpu/drm/stm/ltdc.h

@@ -21,6 +21,7 @@ struct ltdc_caps {
 	bool non_alpha_only_l1; /* non-native no-alpha formats on layer 1 */
 	int pad_max_freq_hz;	/* max frequency supported by pad */
 	int nb_irq;		/* number of hardware interrupts */
+	bool ycbcr_output;	/* ycbcr output converter supported */
 };
 
 #define LTDC_MAX_LAYER	4