Patch "drm/i915/dp: Write to SET_POWER dpcd to enable MST hub." has been added to the 4.15-stable tree

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

drm/i915/dp: Write to SET_POWER dpcd to enable MST hub.

to the 4.15-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-write-to-set_power-dpcd-to-enable-mst-hub.patch

and it can be found in the queue-4.15 subdirectory.

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

From: Dhinakaran Pandiyan <[email protected]>
Date: Tue, 13 Mar 2018 22:48:25 -0700
Subject: drm/i915/dp: Write to SET_POWER dpcd to enable MST hub.
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From: Dhinakaran Pandiyan <[email protected]>

commit b1e314462bba76660eec62760bb2e87f28f58866 upstream.

If bios sets up an MST output and hardware state readout code sees this is an SST configuration, when disabling the encoder we end up calling ->post_disable_dp() hook instead of the MST version. Consequently, we write to the DP_SET_POWER dpcd to set it D3 state. Further along when we try enable the encoder in MST mode, POWER_UP_PHY transaction fails to power up the MST hub. This results in continuous link training failures which keep the system busy delaying boot. We could identify bios MST boot discrepancy and handle it accordingly but a simple way to solve this is to write to the DP_SET_POWER dpcd for MST too.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105470

---
 drivers/gpu/drm/i915/intel_ddi.c |   12 ++----------
 1 file changed, 2 insertions(+), 10 deletions(-)

@@ -2208,8 +2208,7 @@ static void intel_ddi_pre_enable_dp(stru
 		intel_prepare_dp_ddi_buffers(encoder);
 
 	intel_ddi_init_dp_buf_reg(encoder);
-	if (!is_mst)
-		intel_dp_sink_dpms(intel_dp, DRM_MODE_DPMS_ON);
+	intel_dp_sink_dpms(intel_dp, DRM_MODE_DPMS_ON);
 	intel_dp_start_link_train(intel_dp);
 	if (port != PORT_A || INTEL_GEN(dev_priv) >= 9)
 		intel_dp_stop_link_train(intel_dp);

@@ -2294,19 +2293,12 @@ static void intel_ddi_post_disable_dp(st
 	struct drm_i915_private *dev_priv = to_i915(encoder->base.dev);
 	struct intel_digital_port *dig_port = enc_to_dig_port(&encoder->base);
 	struct intel_dp *intel_dp = &dig_port->dp;
-	/*
-	 * old_crtc_state and old_conn_state are NULL when called from
-	 * DP_MST. The main connector associated with this port is never
-	 * bound to a crtc for MST.
-	 */
-	bool is_mst = !old_crtc_state;
 
 	/*
 	 * Power down sink before disabling the port, otherwise we end
 	 * up getting interrupts from the sink on detecting link loss.
 	 */
-	if (!is_mst)
-		intel_dp_sink_dpms(intel_dp, DRM_MODE_DPMS_OFF);
+	intel_dp_sink_dpms(intel_dp, DRM_MODE_DPMS_OFF);
 
 	intel_disable_ddi_buf(encoder);
 

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

queue-4.15/drm-i915-dp-write-to-set_power-dpcd-to-enable-mst-hub.patch