[PATCH 16/18] drm/i915: lock around link status and link training.

[Dariusz Gadomski]

From: Dave Airlie <airlied at redhat.com>

BugLink: https://bugs.launchpad.net/bugs/1104230

We need to take the connection mutex around the link status
check for non-MST case, but also around the MST link training
on short HPDs.

I suspect we actually should have a dpcd lock in the future as
well, that just lock the local copies of dpcd and flags stored
from that.

Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
Signed-off-by: Dave Airlie <airlied at redhat.com>
(cherry picked from commit 1c306fcd8a18519e4247060dd85a534c6ce29c1d upstream)
Signed-off-by: Dariusz Gadomski <dariusz.gadomski at canonical.com>
---
 drivers/gpu/drm/i915/intel_dp.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 52dd196..b17e7e7 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -3400,11 +3400,13 @@ intel_dp_check_mst_status(struct intel_dp *intel_dp)
 void
 intel_dp_check_link_status(struct intel_dp *intel_dp)
 {
+	struct drm_device *dev = intel_dp_to_dev(intel_dp);
 	struct intel_encoder *intel_encoder = &dp_to_dig_port(intel_dp)->base;
 	u8 sink_irq_vector;
 	u8 link_status[DP_LINK_STATUS_SIZE];
 
-	/* FIXME: This access isn't protected by any locks. */
+	WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex));
+
 	if (!intel_encoder->connectors_active)
 		return;
 
@@ -3931,7 +3933,9 @@ intel_dp_hpd_pulse(struct intel_digital_port *intel_dig_port, bool long_hpd)
 			 * 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);
 		}
 	}
 	return false;
-- 
1.9.1