[PATCH V3 2/3] drm/bridge: dw-hdmi-qp: Add support for missing HPD

[Chris Morgan]

From: Chris Morgan <macromorgan at hotmail.com>

Add support for the dw-hdmi-qp driver to handle devices with missing
HPD pins.

Since in this situation we are now polling for the EDID data via i2c
change the error message to a rate limited debug message when we are
unable to complete an i2c read, as a disconnected device would
otherwise fill dmesg with i2c read errors.

Reviewed-by: Cristian Ciocaltea <cristian.ciocaltea at collabora.com>
Signed-off-by: Chris Morgan <macromorgan at hotmail.com>
---
 drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c | 34 +++++++++++++++++---
 1 file changed, 30 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c
index 39332c57f2c5..929b2e95a5c5 100644
--- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c
+++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi-qp.c
@@ -145,6 +145,7 @@ struct dw_hdmi_qp {
 	struct regmap *regm;
 
 	unsigned long tmds_char_rate;
+	bool no_hpd;
 };
 
 static void dw_hdmi_qp_write(struct dw_hdmi_qp *hdmi, unsigned int val,
@@ -535,14 +536,22 @@ static int dw_hdmi_qp_i2c_read(struct dw_hdmi_qp *hdmi,
 
 		stat = wait_for_completion_timeout(&i2c->cmp, HZ / 10);
 		if (!stat) {
-			dev_err(hdmi->dev, "i2c read timed out\n");
+			if (hdmi->no_hpd)
+				dev_dbg_ratelimited(hdmi->dev,
+						    "i2c read timed out\n");
+			else
+				dev_err(hdmi->dev, "i2c read timed out\n");
 			dw_hdmi_qp_write(hdmi, 0x01, I2CM_CONTROL0);
 			return -EAGAIN;
 		}
 
 		/* Check for error condition on the bus */
 		if (i2c->stat & I2CM_NACK_RCVD_IRQ) {
-			dev_err(hdmi->dev, "i2c read error\n");
+			if (hdmi->no_hpd)
+				dev_dbg_ratelimited(hdmi->dev,
+						    "i2c read error\n");
+			else
+				dev_err(hdmi->dev, "i2c read error\n");
 			dw_hdmi_qp_write(hdmi, 0x01, I2CM_CONTROL0);
 			return -EIO;
 		}
@@ -879,6 +888,15 @@ static enum drm_connector_status
 dw_hdmi_qp_bridge_detect(struct drm_bridge *bridge, struct drm_connector *connector)
 {
 	struct dw_hdmi_qp *hdmi = bridge->driver_private;
+	const struct drm_edid *drm_edid;
+
+	if (hdmi->no_hpd) {
+		drm_edid = drm_edid_read_ddc(connector, bridge->ddc);
+		if (drm_edid)
+			return connector_status_connected;
+		else
+			return connector_status_disconnected;
+	}
 
 	return hdmi->phy.ops->read_hpd(hdmi, hdmi->phy.data);
 }
@@ -904,6 +922,11 @@ dw_hdmi_qp_bridge_tmds_char_rate_valid(const struct drm_bridge *bridge,
 {
 	struct dw_hdmi_qp *hdmi = bridge->driver_private;
 
+	/*
+	 * TODO: when hdmi->no_hpd is 1 we must not support modes that
+	 * require scrambling, including every mode with a clock above
+	 * HDMI14_MAX_TMDSCLK.
+	 */
 	if (rate > HDMI14_MAX_TMDSCLK) {
 		dev_dbg(hdmi->dev, "Unsupported TMDS char rate: %lld\n", rate);
 		return MODE_CLOCK_HIGH;
@@ -1074,12 +1097,15 @@ struct dw_hdmi_qp *dw_hdmi_qp_bind(struct platform_device *pdev,
 	if (ret)
 		return ERR_PTR(ret);
 
+	hdmi->no_hpd = device_property_read_bool(dev, "no-hpd");
+
 	hdmi->bridge.driver_private = hdmi;
 	hdmi->bridge.ops = DRM_BRIDGE_OP_DETECT |
 			   DRM_BRIDGE_OP_EDID |
 			   DRM_BRIDGE_OP_HDMI |
-			   DRM_BRIDGE_OP_HDMI_AUDIO |
-			   DRM_BRIDGE_OP_HPD;
+			   DRM_BRIDGE_OP_HDMI_AUDIO;
+	if (!hdmi->no_hpd)
+		hdmi->bridge.ops |= DRM_BRIDGE_OP_HPD;
 	hdmi->bridge.of_node = pdev->dev.of_node;
 	hdmi->bridge.type = DRM_MODE_CONNECTOR_HDMIA;
 	hdmi->bridge.vendor = "Synopsys";
-- 
2.43.0