Patch "drm/i915/dp: add lane_count check in intel_dp_check_link_status" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

drm/i915/dp: add lane_count check in intel_dp_check_link_status

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
drm-i915-dp-add-lane_count-check-in-intel_dp_check_link_status.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Matthew Auld <[email protected]>
Date: Wed, 19 Oct 2016 22:29:53 +0100
Subject: drm/i915/dp: add lane_count check in intel_dp_check_link_status
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From: Matthew Auld <[email protected]>

commit d4cb3fd9b548b8bfe2a712ec920b9ebabd3547ab upstream.

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.

v2: add WARN_ON_ONCE and FIXME comment (Ville)

References: https://bugs.freedesktop.org/show_bug.cgi?id=97344

---
 drivers/gpu/drm/i915/intel_dp.c |    5 +++++
 1 file changed, 5 insertions(+)

@@ -4018,6 +4018,11 @@ intel_dp_check_link_status(struct intel_
 	if (!to_intel_crtc(intel_encoder->base.crtc)->active)
 		return;
 
+	/* FIXME: we need to synchronize this sort of stuff with hardware
+	 * readout */
+	if (WARN_ON_ONCE(!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))) {

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/drm-i915-dp-add-lane_count-check-in-intel_dp_check_link_status.patch