usb: typec: altmodes/displayport: Signal hpd when configuring pin assignment

When connecting to some DisplayPort partners, the initial status update
after entering DisplayPort Alt Mode notifies that the DFP_D/UFP_D is not in
the connected state. This leads to sending a configure message that keeps
the device in USB mode. The port partner then sets DFP_D/UFP_D to the
connected state and HPD to high in the same Attention message. Currently,
the HPD signal is dropped in order to handle configuration.

This patch saves changes to the HPD signal when the device chooses to
configure during dp_altmode_status_update, and invokes sysfs_notify if
necessary for HPD after configuring.

Fixes: 0e3bb7d6 ("usb: typec: Add driver for DisplayPort alternate mode")
Cc: stable@vger.kernel.org
Signed-off-by: RD Babiera <rdbabiera@google.com>
Acked-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Link: https://lore.kernel.org/r/20230726020903.1409072-1-rdbabiera@google.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/typec/altmodes/displayport.c

@@ -60,6 +60,7 @@ struct dp_altmode {
 
 	enum dp_state state;
 	bool hpd;
+	bool pending_hpd;
 
 	struct mutex lock; /* device lock */
 	struct work_struct work;
@@ -144,8 +145,13 @@ static int dp_altmode_status_update(struct dp_altmode *dp)
 		dp->state = DP_STATE_EXIT;
 	} else if (!(con & DP_CONF_CURRENTLY(dp->data.conf))) {
 		ret = dp_altmode_configure(dp, con);
-		if (!ret)
+		if (!ret) {
 			dp->state = DP_STATE_CONFIGURE;
+			if (dp->hpd != hpd) {
+				dp->hpd = hpd;
+				dp->pending_hpd = true;
+			}
+		}
 	} else {
 		if (dp->hpd != hpd) {
 			drm_connector_oob_hotplug_event(dp->connector_fwnode);
@@ -161,6 +167,16 @@ static int dp_altmode_configured(struct dp_altmode *dp)
 {
 	sysfs_notify(&dp->alt->dev.kobj, "displayport", "configuration");
 	sysfs_notify(&dp->alt->dev.kobj, "displayport", "pin_assignment");
+	/*
+	 * If the DFP_D/UFP_D sends a change in HPD when first notifying the
+	 * DisplayPort driver that it is connected, then we wait until
+	 * configuration is complete to signal HPD.
+	 */
+	if (dp->pending_hpd) {
+		drm_connector_oob_hotplug_event(dp->connector_fwnode);
+		sysfs_notify(&dp->alt->dev.kobj, "displayport", "hpd");
+		dp->pending_hpd = false;
+	}
 
 	return dp_altmode_notify(dp);
 }