[RFC 08/11] drm/bridge: synopsys: dw-hdmi: add 420 mode format negociation

[Neil Armstrong]

Add special negociation case for 420 HDMI2.0 format.

In this case the DW-HDMI CSC cannot handle 420 data, and must be
in passthrought, thus input_bus_cfg must be output_bus_cfg.

Add support for handling a specific 8/10/12/16 variant in the connector
bus_formats if specified.

Signed-off-by: Neil Armstrong <narmstrong@xxxxxxxxxxxx>
---
 drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 45 ++++++++++++++++++-----
 1 file changed, 36 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
index cb560b231d74..b96119c6fad2 100644
--- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
+++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
@@ -2213,23 +2213,50 @@ static int dw_hdmi_bridge_atomic_check(struct drm_bridge *bridge,
 				       struct drm_connector_state *conn_state)
 {
 	struct dw_hdmi *hdmi = bridge->driver_private;
+	struct drm_connector *conn = conn_state->connector;
+	struct drm_display_info *info = &conn->display_info;
+	struct drm_display_mode *mode = &crtc_state->mode;
+	bool is_hdmi2_sink = info->hdmi.scdc.supported;
 	int ret;
 
-	ret = drm_atomic_bridge_choose_output_bus_cfg(bridge_state, crtc_state,
-						      conn_state);
-	if (ret)
-		return ret;
+	/*
+	 * If the current mode enforces 4:2:0, force the output but format
+	 * or use the connector bus formats if a non 8bit 4:2:0 format
+	 * is provided.
+	 */
+	if (drm_mode_is_420_only(info, mode) ||
+		(!is_hdmi2_sink && drm_mode_is_420_also(info, mode))) {
+		if (info->num_bus_formats && info->bus_formats &&
+		    hdmi_bus_fmt_is_yuv420(info->bus_formats[0]))
+			bridge_state->output_bus_cfg.fmt = info->bus_formats[0];
+		else
+			bridge_state->output_bus_cfg.fmt =
+					MEDIA_BUS_FMT_UYYVYY8_0_5X24;
+	} else {
+		ret = drm_atomic_bridge_choose_output_bus_cfg(bridge_state,
+							      crtc_state,
+							      conn_state);
+		if (ret)
+			return ret;
+	}
+
+	if (hdmi_bus_fmt_is_yuv420(bridge_state->output_bus_cfg.fmt)) {
+		/* The DW-HDMI CSC cannot interpolate and decimate in 4:2:0 */
+		bridge_state->input_bus_cfg.fmt =
+			bridge_state->output_bus_cfg.fmt;
+	} else {
+		ret = drm_atomic_bridge_choose_input_bus_cfg(bridge_state,
+				                             crtc_state,
+							     conn_state);
+		if (ret)
+			return ret;
+	}
 
 	dev_dbg(hdmi->dev, "selected output format %x\n",
 			bridge_state->output_bus_cfg.fmt);
 
 	hdmi->hdmi_data.enc_out_bus_format = bridge_state->output_bus_cfg.fmt;
 
-	ret = drm_atomic_bridge_choose_input_bus_cfg(bridge_state, crtc_state,
-						      conn_state);
-	if (ret)
-		return ret;
-
 	dev_dbg(hdmi->dev, "selected input format %x\n",
 			bridge_state->input_bus_cfg.fmt);
 
-- 
2.22.0