[Intel-gfx] [stable:v4.15] drm/i915/dp: Write to SET_POWER dpcd to enable MST hub.

[Dhinakaran Pandiyan]

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.

v2: Rebased on stable/linux-4.15.y and fixed minor conflict.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105470
Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
Cc: Jani Nikula <jani.nikula at intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
Reported-by: Laura Abbott <labbott at redhat.com>
Cc: <stable at vger.kernel.org> # 4.15+
Fixes: 5ea2355a100a ("drm/i915/mst: Use MST sideband message transactions for dpms control")
Tested-by: Laura Abbott <labbott at redhat.com>
Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com>
Signed-off-by: Jani Nikula <jani.nikula at intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180314054825.1718-1-dhinakaran.pandiyan@intel.com
(cherry picked from commit ad260ab32a4d94fa974f58262f8000472d34fd5b)
Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com>
---
 drivers/gpu/drm/i915/intel_ddi.c | 12 ++----------
 1 file changed, 2 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
index 58a3755544b2..38e53d6b8127 100644
--- a/drivers/gpu/drm/i915/intel_ddi.c
+++ b/drivers/gpu/drm/i915/intel_ddi.c
@@ -2208,8 +2208,7 @@ static void intel_ddi_pre_enable_dp(struct intel_encoder *encoder,
 		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(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;
-	/*
-	 * 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);
 
-- 
2.14.1