[PATCH] drm: bridge: dw_hdmi: only trigger hotplug event on real link state change

[Lucas Stach]

There are two events that signal a real change of the link state: HPD going
high means the sink is newly connected or wants the source to re-read the
EDID, RX sense going low is a indication that the link has been disconnected.

Ignore the other two events that also trigger interrupts, but don't need
immediate attention: HPD going low does not necessarily mean the link has
been lost and should not trigger a immediate read of the status. RX sense
going high also does not require a detect cycle, as HPD going high is the
right point in time to read the EDID.

Ignoring the negative HPD edge does make the detection much more robust
against spurious link status changes due to EMI or marginal signal levels.

Signed-off-by: Lucas Stach <l.stach at pengutronix.de>
---
 drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
index 3e1be9894ed1..24f991b5248d 100644
--- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
+++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
@@ -3095,6 +3095,7 @@ 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;
+	enum drm_connector_status status = connector_status_unknown;
 
 	intr_stat = hdmi_readb(hdmi, HDMI_IH_PHY_STAT0);
 	phy_int_pol = hdmi_readb(hdmi, HDMI_PHY_POL0);
@@ -3133,13 +3134,15 @@ static irqreturn_t dw_hdmi_irq(int irq, void *dev_id)
 			cec_notifier_phys_addr_invalidate(hdmi->cec_notifier);
 			mutex_unlock(&hdmi->cec_notifier_mutex);
 		}
-	}
 
-	if (intr_stat & HDMI_IH_PHY_STAT0_HPD) {
-		enum drm_connector_status status = phy_int_pol & HDMI_PHY_HPD
-						 ? connector_status_connected
-						 : connector_status_disconnected;
+		if (phy_stat & HDMI_PHY_HPD)
+			status = connector_status_connected;
+
+		if (!( phy_stat & HDMI_PHY_RX_SENSE))
+			status = connector_status_disconnected;
+	}
 
+	if (status != connector_status_unknown) {
 		dev_dbg(hdmi->dev, "EVENT=%s\n",
 			status == connector_status_connected ?
 			"plugin" : "plugout");
-- 
2.30.2