drm/bridge: adv7511: Reset registers on hotplug

BugLink: https://bugs.launchpad.net/bugs/1792392

[ Upstream commit 5f341756 ]

The bridge loses its hw state when the cable is unplugged. If we detect
this case in the hpd handler, reset its state.
Reported-by: Rob Clark <robdclark@gmail.com>
Tested-by: Rob Clark <robdclark@gmail.com>
Reviewed-by: Archit Taneja <architt@codeaurora.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20180703165648.120401-1-seanpaul@chromium.orgSigned-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

drivers/gpu/drm/i2c/adv7511.c

@@ -450,6 +450,18 @@ static void adv7511_hpd_work(struct work_struct *work)
 	else
 		status = connector_status_disconnected;
 
+	/*
+	 * The bridge resets its registers on unplug. So when we get a plug
+	 * event and we're already supposed to be powered, cycle the bridge to
+	 * restore its state.
+	 */
+	if (status == connector_status_connected &&
+	    adv7511->connector.status == connector_status_disconnected &&
+	    adv7511->powered) {
+		regcache_mark_dirty(adv7511->regmap);
+		adv7511_power_on(adv7511);
+	}
+
 	if (adv7511->connector.status != status) {
 		adv7511->connector.status = status;
 		drm_kms_helper_hotplug_event(adv7511->connector.dev);