FAILED: patch "[PATCH] drm/i915/dp: Write to SET_POWER dpcd to enable MST hub." failed to apply to 4.15-stable tree

The patch below does not apply to the 4.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

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

index f51645a08dca..6aff9d096e13 100644
@@ -2175,8 +2175,7 @@ static void intel_ddi_pre_enable_dp(struct intel_encoder *encoder,
 		intel_prepare_dp_ddi_buffers(encoder, crtc_state);
 
 	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);

@@ -2274,14 +2273,12 @@ static void intel_ddi_post_disable_dp(struct intel_encoder *encoder,
 	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;
-	bool is_mst = intel_crtc_has_type(old_crtc_state, INTEL_OUTPUT_DP_MST);
 
 	/*
 	 * 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);