[PATCH] drm/i915/dp: add lane_count check in intel_dp_check_link_status

[Matthew Auld <matthew.auld@intel.com>]

Currently it's entirely possible to go through the link training step
without first determining the lane_count, which is silly since we end up
doing a bunch of aux transfers of size = 0, as highlighted by
WARN_ON(!msg->buffer != !msg->size), and can only ever result in a
'failed to update link training' message. This can be observed during
intel_dp_long_pulse where we can do the link training step, but before
we have had a chance to set the link params. To avoid this we add an
extra check for the lane_count in intel_dp_check_link_status, which
should prevent us from doing the link training step prematurely.

References: https://bugs.freedesktop.org/show_bug.cgi?id=97344
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
---
 drivers/gpu/drm/i915/intel_dp.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index a3c7dd8..0dbb672 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -3927,6 +3927,9 @@ intel_dp_check_link_status(struct intel_dp *intel_dp)
 	if (!to_intel_crtc(intel_encoder->base.crtc)->active)
 		return;
 
+	if (!intel_dp->lane_count)
+		return;
+
 	/* if link training is requested we should perform it always */
 	if ((intel_dp->compliance_test_type == DP_TEST_LINK_TRAINING) ||
 	    (!drm_dp_channel_eq_ok(link_status, intel_dp->lane_count))) {
-- 
2.7.4

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