usb: typec: altmodes/displayport: Signal hpd low when exiting mode

Upon receiving an ACK for a sent EXIT_MODE message, the DisplayPort
driver currently resets the status and configuration of the port partner.
The hpd signal is not updated despite being part of the status, so the
Display stack can still transmit video despite typec_altmode_exit placing
the lanes in a Safe State.

Set hpd to low when a sent EXIT_MODE message is ACK'ed.

Fixes: 0e3bb7d ("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/20231009210057.3773877-2-rdbabiera@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: RD Babiera

drivers/usb/typec/altmodes/displayport.c

@@ -304,6 +304,11 @@ static int dp_altmode_vdm(struct typec_altmode *alt,
 			typec_altmode_update_active(alt, false);
 			dp->data.status = 0;
 			dp->data.conf = 0;
+			if (dp->hpd) {
+				drm_connector_oob_hotplug_event(dp->connector_fwnode);
+				dp->hpd = false;
+				sysfs_notify(&dp->alt->dev.kobj, "displayport", "hpd");
+			}
 			break;
 		case DP_CMD_STATUS_UPDATE:
 			dp->data.status = *vdo;