[PATCH 4/4] drm: bridge/dw-hdmi: use rx sense for plug detection if hpd is unreliable

[Philipp Zabel]

Due to the voltage divider on the HPD line, the HDMI connector on
imx6q-sabrelite doesn't reliably detect connected DVI monitors.
This patch allows to use the RX_SENSE signals as a workaround when
enabled by a boolean device tree property 'hpd-unreliable'.

Signed-off-by: Philipp Zabel <p.zabel at pengutronix.de>
---
 drivers/gpu/drm/bridge/dw-hdmi.c | 30 ++++++++++++++++++++----------
 1 file changed, 20 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/bridge/dw-hdmi.c b/drivers/gpu/drm/bridge/dw-hdmi.c
index 2388a55..7ffaa44 100644
--- a/drivers/gpu/drm/bridge/dw-hdmi.c
+++ b/drivers/gpu/drm/bridge/dw-hdmi.c
@@ -111,6 +111,7 @@ struct dw_hdmi {
 	struct device *dev;
 	struct clk *isfr_clk;
 	struct clk *iahb_clk;
+	bool hpd_unreliable;
 
 	struct hdmi_data_info hdmi_data;
 	const struct dw_hdmi_plat_data *plat_data;
@@ -1413,6 +1414,8 @@ dw_hdmi_connector_detect(struct drm_connector *connector, bool force)
 {
 	struct dw_hdmi *hdmi = container_of(connector, struct dw_hdmi,
 					     connector);
+	/* If HPD is not reliable, use RX_SENSE as fallback */
+	u8 stat_mask = hdmi->hpd_unreliable ? HDMI_PHY_RX_SENSE : HDMI_PHY_HPD;
 
 	mutex_lock(&hdmi->mutex);
 	hdmi->force = DRM_FORCE_UNSPECIFIED;
@@ -1420,7 +1423,7 @@ dw_hdmi_connector_detect(struct drm_connector *connector, bool force)
 	dw_hdmi_update_phy_mask(hdmi);
 	mutex_unlock(&hdmi->mutex);
 
-	if (hdmi_readb(hdmi, HDMI_PHY_STAT0) & HDMI_PHY_HPD)
+	if ((hdmi_readb(hdmi, HDMI_PHY_STAT0) & stat_mask) == stat_mask)
 		return connector_status_connected;
 
 	/* free previous EDID block */
@@ -1556,7 +1559,7 @@ static irqreturn_t dw_hdmi_hardirq(int irq, void *dev_id)
 static irqreturn_t dw_hdmi_irq(int irq, void *dev_id)
 {
 	struct dw_hdmi *hdmi = dev_id;
-	u8 intr_stat, phy_int_pol, phy_pol_mask, phy_stat;
+	u8 intr_stat, intr_mask, phy_int_pol, phy_pol_mask, phy_stat;
 
 	intr_stat = hdmi_readb(hdmi, HDMI_IH_PHY_STAT0);
 	phy_int_pol = hdmi_readb(hdmi, HDMI_PHY_POL0);
@@ -1583,9 +1586,12 @@ static irqreturn_t dw_hdmi_irq(int irq, void *dev_id)
 	 * other end of the link.  Use this to decide whether we should
 	 * power on the phy as HPD may be toggled by the sink to merely
 	 * ask the source to re-read the EDID.
+	 * If HPD is known to be unreliable, ignore it completely.
 	 */
-	if (intr_stat &
-	    (HDMI_IH_PHY_STAT0_RX_SENSE | HDMI_IH_PHY_STAT0_HPD)) {
+	intr_mask = hdmi->hpd_unreliable ?
+		    HDMI_IH_PHY_STAT0_RX_SENSE :
+		    HDMI_IH_PHY_STAT0_RX_SENSE | HDMI_IH_PHY_STAT0_HPD;
+	if (intr_stat & intr_mask) {
 		mutex_lock(&hdmi->mutex);
 		if (!hdmi->disabled && !hdmi->force) {
 			/*
@@ -1594,14 +1600,14 @@ static irqreturn_t dw_hdmi_irq(int irq, void *dev_id)
 			 */
 			if (!(phy_stat & HDMI_PHY_RX_SENSE))
 				hdmi->rxsense = false;
-
 			/*
 			 * Only set the software rxsense status when both
 			 * rxsense and hpd indicates we're connected.
 			 * This avoids what seems to be bad behaviour in
 			 * at least iMX6S versions of the phy.
 			 */
-			if (phy_stat & HDMI_PHY_HPD)
+			else if ((phy_stat & HDMI_PHY_HPD) ||
+				 hdmi->hpd_unreliable)
 				hdmi->rxsense = true;
 
 			dw_hdmi_update_power(hdmi);
@@ -1617,8 +1623,7 @@ static irqreturn_t dw_hdmi_irq(int irq, void *dev_id)
 	}
 
 	hdmi_writeb(hdmi, intr_stat, HDMI_IH_PHY_STAT0);
-	hdmi_writeb(hdmi, ~(HDMI_IH_PHY_STAT0_HPD | HDMI_IH_PHY_STAT0_RX_SENSE),
-		    HDMI_IH_MUTE_PHY_STAT0);
+	hdmi_writeb(hdmi, ~intr_mask, HDMI_IH_MUTE_PHY_STAT0);
 
 	return IRQ_HANDLED;
 }
@@ -1679,6 +1684,7 @@ int dw_hdmi_bind(struct device *dev, struct device *master,
 	struct device_node *ddc_node;
 	struct dw_hdmi_audio_data audio;
 	struct dw_hdmi *hdmi;
+	u8 intr_mask;
 	int ret;
 	u32 val = 1;
 
@@ -1770,6 +1776,8 @@ int dw_hdmi_bind(struct device *dev, struct device *master,
 
 	initialize_hdmi_ih_mutes(hdmi);
 
+	hdmi->hpd_unreliable = of_property_read_bool(np, "hpd-unreliable");
+
 	ret = devm_request_threaded_irq(dev, irq, dw_hdmi_hardirq,
 					dw_hdmi_irq, IRQF_SHARED,
 					dev_name(dev), hdmi);
@@ -1801,8 +1809,10 @@ int dw_hdmi_bind(struct device *dev, struct device *master,
 		goto err_iahb;
 
 	/* Unmute interrupts */
-	hdmi_writeb(hdmi, ~(HDMI_IH_PHY_STAT0_HPD | HDMI_IH_PHY_STAT0_RX_SENSE),
-		    HDMI_IH_MUTE_PHY_STAT0);
+	intr_mask = hdmi->hpd_unreliable ?
+		    HDMI_IH_PHY_STAT0_RX_SENSE :
+		    HDMI_IH_PHY_STAT0_RX_SENSE | HDMI_IH_PHY_STAT0_HPD;
+	hdmi_writeb(hdmi, ~intr_mask, HDMI_IH_MUTE_PHY_STAT0);
 
 	memset(&pdevinfo, 0, sizeof(pdevinfo));
 	pdevinfo.parent = dev;
-- 
2.6.4