[PATCH] drm: ignore disconnected <-> unknown status changes

[Knut Petersen <Knut_Petersen@t-online.de>]

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On an AOpen i915GMm-hfs the hotplug events generated
by transitions between connector_status_unknown and
connector_status_disconnected cause screen distortions.

The attached patch cures the problem by disabling the
generation of hotplug events in those cases. That should
be safe for everybody as the only relevant changes are
those from / to connector_status_connected.

cu,
  Knut

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>From f631128c46f916eb58bbdabf867248a04a0d2fc5 Mon Sep 17 00:00:00 2001
From: Knut Petersen <Knut_Petersen@t-online.de>
Date: Thu, 2 Aug 2012 08:52:04 +0200
Subject: [PATCH] drm: ignore disconnected <-> unknown status changes

Only generate a hotplug event if the status changed
to / from connector_status_connected.

On some hardware the connector status is oscillating
between disconnected and unknown, and the hotplug
events mirroring these transitions cause screen
distortions. As the only reasonable action on such
a status change is to ignore it, it also is safe
not to genereate a hotplug event at all.

Needed for / tested on AOpen i915GMm-hfs mobo.

Signed-off-by: Knut Petersen <Knut_Petersen@t-online.de>
---
 drivers/gpu/drm/drm_crtc_helper.c |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)

diff --git a/drivers/gpu/drm/drm_crtc_helper.c b/drivers/gpu/drm/drm_crtc_helper.c
index 3252e70..fb6160b 100644
--- a/drivers/gpu/drm/drm_crtc_helper.c
+++ b/drivers/gpu/drm/drm_crtc_helper.c
@@ -954,7 +954,11 @@ static void output_poll_execute(struct work_struct *work)
 			      connector->base.id,
 			      drm_get_connector_name(connector),
 			      old_status, connector->status);
-		if (old_status != connector->status)
+		/* changes are only relevant if previous or
+		    current status is connector_status_connected */
+		if (old_status != connector->status &&
+		    (old_status == connector_status_connected ||
+		    connector->status == connector_status_connected))
 			changed = true;
 	}
 
-- 
1.7.7