drm/dp: Add helpers for DFP YCbCr 4:2:0 handling

Add helpers to determine whether the DFP supports
YCbCr 4:2:0 passthrough or YCbCr 4:4:4->4:2:0 conversion.

v2: Add kdocs (Lyude)
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200904115354.25336-18-ville.syrjala@linux.intel.comReviewed-by: Lyude Paul <lyude@redhat.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/drm_dp_helper.c

@@ -808,6 +808,66 @@ int drm_dp_downstream_max_bpc(const u8 dpcd[DP_RECEIVER_CAP_SIZE],
 }
 EXPORT_SYMBOL(drm_dp_downstream_max_bpc);
 
+/**
+ * drm_dp_downstream_420_passthrough() - determine downstream facing port
+ *                                       YCbCr 4:2:0 pass-through capability
+ * @dpcd: DisplayPort configuration data
+ * @port_cap: downstream facing port capabilities
+ *
+ * Returns: whether the downstream facing port can pass through YCbCr 4:2:0
+ */
+bool drm_dp_downstream_420_passthrough(const u8 dpcd[DP_RECEIVER_CAP_SIZE],
+				       const u8 port_cap[4])
+{
+	if (!drm_dp_is_branch(dpcd))
+		return false;
+
+	if (dpcd[DP_DPCD_REV] < 0x13)
+		return false;
+
+	switch (port_cap[0] & DP_DS_PORT_TYPE_MASK) {
+	case DP_DS_PORT_TYPE_DP:
+		return true;
+	case DP_DS_PORT_TYPE_HDMI:
+		if ((dpcd[DP_DOWNSTREAMPORT_PRESENT] & DP_DETAILED_CAP_INFO_AVAILABLE) == 0)
+			return false;
+
+		return port_cap[3] & DP_DS_HDMI_YCBCR420_PASS_THROUGH;
+	default:
+		return false;
+	}
+}
+EXPORT_SYMBOL(drm_dp_downstream_420_passthrough);
+
+/**
+ * drm_dp_downstream_444_to_420_conversion() - determine downstream facing port
+ *                                             YCbCr 4:4:4->4:2:0 conversion capability
+ * @dpcd: DisplayPort configuration data
+ * @port_cap: downstream facing port capabilities
+ *
+ * Returns: whether the downstream facing port can convert YCbCr 4:4:4 to 4:2:0
+ */
+bool drm_dp_downstream_444_to_420_conversion(const u8 dpcd[DP_RECEIVER_CAP_SIZE],
+					     const u8 port_cap[4])
+{
+	if (!drm_dp_is_branch(dpcd))
+		return false;
+
+	if (dpcd[DP_DPCD_REV] < 0x13)
+		return false;
+
+	switch (port_cap[0] & DP_DS_PORT_TYPE_MASK) {
+	case DP_DS_PORT_TYPE_HDMI:
+		if ((dpcd[DP_DOWNSTREAMPORT_PRESENT] & DP_DETAILED_CAP_INFO_AVAILABLE) == 0)
+			return false;
+
+		return port_cap[3] & DP_DS_HDMI_YCBCR444_TO_420_CONV;
+	default:
+		return false;
+	}
+}
+EXPORT_SYMBOL(drm_dp_downstream_444_to_420_conversion);
+
 /**
  * drm_dp_downstream_mode() - return a mode for downstream facing port
  * @dpcd: DisplayPort configuration data

include/drm/drm_dp_helper.h

@@ -407,6 +407,10 @@ struct drm_device;
 # define DP_DS_DVI_HIGH_COLOR_DEPTH	    (1 << 2)
 /* offset 3 for HDMI */
 # define DP_DS_HDMI_FRAME_SEQ_TO_FRAME_PACK (1 << 0)
+# define DP_DS_HDMI_YCBCR422_PASS_THROUGH   (1 << 1)
+# define DP_DS_HDMI_YCBCR420_PASS_THROUGH   (1 << 2)
+# define DP_DS_HDMI_YCBCR444_TO_422_CONV    (1 << 3)
+# define DP_DS_HDMI_YCBCR444_TO_420_CONV    (1 << 4)
 
 #define DP_MAX_DOWNSTREAM_PORTS		    0x10
 
@@ -1663,6 +1667,10 @@ int drm_dp_downstream_min_tmds_clock(const u8 dpcd[DP_RECEIVER_CAP_SIZE],
 int drm_dp_downstream_max_bpc(const u8 dpcd[DP_RECEIVER_CAP_SIZE],
 			      const u8 port_cap[4],
 			      const struct edid *edid);
+bool drm_dp_downstream_420_passthrough(const u8 dpcd[DP_RECEIVER_CAP_SIZE],
+				       const u8 port_cap[4]);
+bool drm_dp_downstream_444_to_420_conversion(const u8 dpcd[DP_RECEIVER_CAP_SIZE],
+					     const u8 port_cap[4]);
 struct drm_display_mode *drm_dp_downstream_mode(struct drm_device *dev,
 						const u8 dpcd[DP_RECEIVER_CAP_SIZE],
 						const u8 port_cap[4]);