[PATCH 3.19.y-ckt 084/156] drm/i915: Check DP link status on long hpd too

[Kamal Mostafa]

3.19.8-ckt8 -stable review patch.  If anyone has any objections, please let me know.

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

From: =?UTF-8?q?Ville=20Syrj=C3=A4l=C3=A4?= <ville.syrjala at linux.intel.com>

commit d14e7b6d1d8747826cb900db852351c550e00fdd upstream.

We are no longer checkling the DP link status on long hpd. We used to do
that from the .hot_plug() handler, but it was removed when MST got
introduced.

If there's no userspace we now fail to retrain the link if the sink
power is toggled (or cable yanked and replugged), meaning the user is
left staring at a blank screen. With the retraining put back that should
be fixed.

Also remove the leftover comment that referred to the old retraining
from .hot_plug().

Fixes a regression introduced in:
commit 0e32b39ceed665bfa4a77a4bc307b6652b991632
Author: Dave Airlie <airlied at redhat.com>
Date:   Fri May 2 14:02:48 2014 +1000

    drm/i915: add DP 1.2 MST support (v0.7)

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=89453
Tested-by: Palmer Dabbelt <palmer at dabbelt.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91407
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=89461
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=89594
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=85641
Cc: Dave Airlie <airlied at redhat.com>
Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula at intel.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/gpu/drm/i915/intel_dp.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 035a458..887f2e4 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -4448,9 +4448,12 @@ intel_dp_hpd_pulse(struct intel_digital_port *intel_dig_port, bool long_hpd)
 
 		intel_dp_probe_oui(intel_dp);
 
-		if (!intel_dp_probe_mst(intel_dp))
+		if (!intel_dp_probe_mst(intel_dp)) {
+			drm_modeset_lock(&dev->mode_config.connection_mutex, NULL);
+			intel_dp_check_link_status(intel_dp);
+			drm_modeset_unlock(&dev->mode_config.connection_mutex);
 			goto mst_fail;
-
+		}
 	} else {
 		if (intel_dp->is_mst) {
 			if (intel_dp_check_mst_status(intel_dp) == -EINVAL)
@@ -4458,10 +4461,6 @@ intel_dp_hpd_pulse(struct intel_digital_port *intel_dig_port, bool long_hpd)
 		}
 
 		if (!intel_dp->is_mst) {
-			/*
-			 * we'll check the link status via the normal hot plug path later -
-			 * but for short hpds we should check it now
-			 */
 			drm_modeset_lock(&dev->mode_config.connection_mutex, NULL);
 			intel_dp_check_link_status(intel_dp);
 			drm_modeset_unlock(&dev->mode_config.connection_mutex);
-- 
1.9.1