linux-kernel - [PATCH 3.16 363/410] drm/radeon: Don't turn off DP sink when disconnected

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Message-ID: <lsq.1528380321.198838328@decadent.org.uk>
Date:   Thu, 07 Jun 2018 15:05:21 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Michel Dänzer" <michel.daenzer@....com>,
        "Alex Deucher" <alexander.deucher@....com>
Subject: [PATCH 3.16 363/410] drm/radeon: Don't turn off DP sink when
 disconnected

3.16.57-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Michel Dänzer <michel.daenzer@....com>

commit 2681bc79eeb640562c932007bfebbbdc55bf6a7d upstream.

Turning off the sink in this case causes various issues, because
userspace expects it to stay on until it turns it off explicitly.

Instead, turn the sink off and back on when a display is connected
again. This dance seems necessary for link training to work correctly.

Bugzilla: https://bugs.freedesktop.org/105308
Reviewed-by: Alex Deucher <alexander.deucher@....com>
Signed-off-by: Michel Dänzer <michel.daenzer@....com>
Signed-off-by: Alex Deucher <alexander.deucher@....com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/gpu/drm/radeon/radeon_connectors.c | 31 +++++++++-------------
 1 file changed, 12 insertions(+), 19 deletions(-)

--- a/drivers/gpu/drm/radeon/radeon_connectors.c
+++ b/drivers/gpu/drm/radeon/radeon_connectors.c
@@ -66,25 +66,18 @@ void radeon_connector_hotplug(struct drm
 		/* don't do anything if sink is not display port, i.e.,
 		 * passive dp->(dvi|hdmi) adaptor
 		 */
-		if (dig_connector->dp_sink_type == CONNECTOR_OBJECT_ID_DISPLAYPORT) {
-			int saved_dpms = connector->dpms;
-			/* Only turn off the display if it's physically disconnected */
-			if (!radeon_hpd_sense(rdev, radeon_connector->hpd.hpd)) {
-				drm_helper_connector_dpms(connector, DRM_MODE_DPMS_OFF);
-			} else if (radeon_dp_needs_link_train(radeon_connector)) {
-				/* Don't try to start link training before we
-				 * have the dpcd */
-				if (!radeon_dp_getdpcd(radeon_connector))
-					return;
+		if (dig_connector->dp_sink_type == CONNECTOR_OBJECT_ID_DISPLAYPORT &&
+		    radeon_hpd_sense(rdev, radeon_connector->hpd.hpd) &&
+		    radeon_dp_needs_link_train(radeon_connector)) {
+			/* Don't start link training before we have the DPCD */
+			if (!radeon_dp_getdpcd(radeon_connector))
+				return;
 
-				/* set it to OFF so that drm_helper_connector_dpms()
-				 * won't return immediately since the current state
-				 * is ON at this point.
-				 */
-				connector->dpms = DRM_MODE_DPMS_OFF;
-				drm_helper_connector_dpms(connector, DRM_MODE_DPMS_ON);
-			}
-			connector->dpms = saved_dpms;
+			/* Turn the connector off and back on immediately, which
+			 * will trigger link training
+			 */
+			drm_helper_connector_dpms(connector, DRM_MODE_DPMS_OFF);
+			drm_helper_connector_dpms(connector, DRM_MODE_DPMS_ON);
 		}
 	}
 }