drm/i915: Filter out glitches on HPD lines during hotplug detection

Glitches deasserting the connector HPD line can lead to incorrectly
detecting a disconnect event (a glitch asserting the line will only
cause a redundant connect->disconnect transition). The source of such a
glitch can be noise on the line or a 0.5ms-1ms MST IRQ_HPD pulse. TypeC
ports in the DP-alt or TBT-alt mode filter out these glitches inernally,
but for others the driver has to do this. Make it so by polling the HPD
line on these connectors for 4 ms.

Link: https://patchwork.freedesktop.org/patch/msgid/20240104083008.2715733-12-imre.deak@intel.comReviewed-by: Jouni Högander <jouni.hogander@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>

drivers/gpu/drm/i915/display/intel_dp.c

@@ -5460,11 +5460,20 @@ bool intel_digital_port_connected_locked(struct intel_encoder *encoder)
 {
 	struct drm_i915_private *dev_priv = to_i915(encoder->base.dev);
 	struct intel_digital_port *dig_port = enc_to_dig_port(encoder);
+	bool is_glitch_free = intel_tc_port_handles_hpd_glitches(dig_port);
 	bool is_connected = false;
 	intel_wakeref_t wakeref;
 
-	with_intel_display_power(dev_priv, POWER_DOMAIN_DISPLAY_CORE, wakeref)
-		is_connected = dig_port->connected(encoder);
+	with_intel_display_power(dev_priv, POWER_DOMAIN_DISPLAY_CORE, wakeref) {
+		unsigned long wait_expires = jiffies + msecs_to_jiffies_timeout(4);
+
+		do {
+			is_connected = dig_port->connected(encoder);
+			if (is_connected || is_glitch_free)
+				break;
+			usleep_range(10, 30);
+		} while (time_before(jiffies, wait_expires));
+	}
 
 	return is_connected;
 }

drivers/gpu/drm/i915/display/intel_tc.c

@@ -122,6 +122,15 @@ bool intel_tc_port_in_legacy_mode(struct intel_digital_port *dig_port)
 	return intel_tc_port_in_mode(dig_port, TC_PORT_LEGACY);
 }
 
+bool intel_tc_port_handles_hpd_glitches(struct intel_digital_port *dig_port)
+{
+	struct drm_i915_private *i915 = to_i915(dig_port->base.base.dev);
+	enum phy phy = intel_port_to_phy(i915, dig_port->base.port);
+	struct intel_tc_port *tc = to_tc_port(dig_port);
+
+	return intel_phy_is_tc(i915, phy) && !tc->legacy_port;
+}
+
 /*
  * The display power domains used for TC ports depending on the
  * platform and TC mode (legacy, DP-alt, TBT):

drivers/gpu/drm/i915/display/intel_tc.h

@@ -15,6 +15,7 @@ struct intel_encoder;
 bool intel_tc_port_in_tbt_alt_mode(struct intel_digital_port *dig_port);
 bool intel_tc_port_in_dp_alt_mode(struct intel_digital_port *dig_port);
 bool intel_tc_port_in_legacy_mode(struct intel_digital_port *dig_port);
+bool intel_tc_port_handles_hpd_glitches(struct intel_digital_port *dig_port);
 
 bool intel_tc_port_connected(struct intel_encoder *encoder);