drm/i915: force full detect on sink count change

This patch checks for changes in sink count between short pulse
hpds and forces full detect when there is a change.

This will allow both detection of hotplug and unplug of panels
through dongles that give only short pulse for such events.

v2: changed variable type from u8 to bool (Jani)
    return immediately if perform_full_detect is set(Siva)

v3: changed method of determining full detection from using
    pointer to return code (Siva)

v4: changed comments to indicate meaning of return value of
    intel_dp_short_pulse and explain the use of return value
    from intel_dp_get_dpcd in intel_dp_short_pulse (Ander)

Tested-by: Nathan D Ciobanu <nathan.d.ciobanu@intel.com>
Signed-off-by: Sivakumar Thulasimani <sivakumar.thulasimani@intel.com>
Signed-off-by: Shubhangi Shrivastava <shubhangi.shrivastava@intel.com>
Reviewed-by: Ander Conselvan de Oliveira <conselvan2@gmail.com>
Signed-off-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1459341326-13142-5-git-send-email-shubhangi.shrivastava@intel.com

drivers/gpu/drm/i915/intel_dp.c

@@ -4273,12 +4273,19 @@ intel_dp_check_link_status(struct intel_dp *intel_dp)
  *  2. Configure link according to Receiver Capabilities
  *  3. Use Link Training from 2.5.3.3 and 3.5.1.3
  *  4. Check link status on receipt of hot-plug interrupt
+ *
+ * intel_dp_short_pulse -  handles short pulse interrupts
+ * when full detection is not required.
+ * Returns %true if short pulse is handled and full detection
+ * is NOT required and %false otherwise.
  */
-static void
+static bool
 intel_dp_short_pulse(struct intel_dp *intel_dp)
 {
 	struct drm_device *dev = intel_dp_to_dev(intel_dp);
 	u8 sink_irq_vector;
+	u8 old_sink_count = intel_dp->sink_count;
+	bool ret;
 
 	/*
 	 * Clearing compliance test variables to allow capturing
@@ -4288,9 +4295,17 @@ intel_dp_short_pulse(struct intel_dp *intel_dp)
 	intel_dp->compliance_test_type = 0;
 	intel_dp->compliance_test_data = 0;
 
-	/* Now read the DPCD to see if it's actually running */
-	if (!intel_dp_get_dpcd(intel_dp)) {
-		return;
+	/*
+	 * Now read the DPCD to see if it's actually running
+	 * If the current value of sink count doesn't match with
+	 * the value that was stored earlier or dpcd read failed
+	 * we need to do full detection
+	 */
+	ret = intel_dp_get_dpcd(intel_dp);
+
+	if ((old_sink_count != intel_dp->sink_count) || !ret) {
+		/* No need to proceed if we are going to do full detect */
+		return false;
 	}
 
 	/* Try to read the source of the interrupt */
@@ -4310,6 +4325,8 @@ intel_dp_short_pulse(struct intel_dp *intel_dp)
 	drm_modeset_lock(&dev->mode_config.connection_mutex, NULL);
 	intel_dp_check_link_status(intel_dp);
 	drm_modeset_unlock(&dev->mode_config.connection_mutex);
+
+	return true;
 }
 
 /* XXX this is probably wrong for multiple downstream ports */
@@ -5043,8 +5060,12 @@ intel_dp_hpd_pulse(struct intel_digital_port *intel_dig_port, bool long_hpd)
 			}
 		}
 
-		if (!intel_dp->is_mst)
-			intel_dp_short_pulse(intel_dp);
+		if (!intel_dp->is_mst) {
+			if (!intel_dp_short_pulse(intel_dp)) {
+				intel_dp_long_pulse(intel_dp->attached_connector);
+				goto put_power;
+			}
+		}
 	}
 
 	ret = IRQ_HANDLED;