i915: Set ddi_pll_sel in DP MST path

The DP MST encoder config function never sets ddi_pll_sel, even though
its value is programmed in its ->pre_enable() hook. That used to work
because a new pipe_config was kzalloc'ed at every modeset, and the value
of zero selects the highest clock for the PLL. Starting with the commit
below, the value of ddi_pll_sel is preserved through modesets, and since
the correct value wasn't properly setup by the MST code, it could lead
to warnings and blank screens.

commit 8504c74c7a
Author: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Date:   Fri May 15 11:51:50 2015 +0300

    drm/i915: Preserve ddi_pll_sel when allocating new pipe_config

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91628
Cc: stable@vger.kernel.org # 7e6313a251 drm/i915: Don't use link_bw for PLL setup
Cc: stable@vger.kernel.org
Cc: Timo Aaltonen <tjaalton@ubuntu.com>
Cc: Luciano Coelho <luciano.coelho@intel.com>
Signed-off-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/intel_dp.c

@@ -1175,7 +1175,7 @@ skl_edp_set_pll_config(struct intel_crtc_state *pipe_config)
 	pipe_config->dpll_hw_state.ctrl1 = ctrl1;
 }
 
-static void
+void
 hsw_dp_set_ddi_pll_sel(struct intel_crtc_state *pipe_config)
 {
 	memset(&pipe_config->dpll_hw_state, 0,

drivers/gpu/drm/i915/intel_dp_mst.c

@@ -33,6 +33,7 @@
 static bool intel_dp_mst_compute_config(struct intel_encoder *encoder,
 					struct intel_crtc_state *pipe_config)
 {
+	struct drm_device *dev = encoder->base.dev;
 	struct intel_dp_mst_encoder *intel_mst = enc_to_mst(&encoder->base);
 	struct intel_digital_port *intel_dig_port = intel_mst->primary;
 	struct intel_dp *intel_dp = &intel_dig_port->dp;
@@ -97,6 +98,10 @@ static bool intel_dp_mst_compute_config(struct intel_encoder *encoder,
 			       &pipe_config->dp_m_n);
 
 	pipe_config->dp_m_n.tu = slots;
+
+	if (IS_HASWELL(dev) || IS_BROADWELL(dev))
+		hsw_dp_set_ddi_pll_sel(pipe_config);
+
 	return true;
 
 }

drivers/gpu/drm/i915/intel_drv.h

@@ -1185,6 +1185,7 @@ void intel_edp_drrs_disable(struct intel_dp *intel_dp);
 void intel_edp_drrs_invalidate(struct drm_device *dev,
 		unsigned frontbuffer_bits);
 void intel_edp_drrs_flush(struct drm_device *dev, unsigned frontbuffer_bits);
+void hsw_dp_set_ddi_pll_sel(struct intel_crtc_state *pipe_config);
 
 /* intel_dp_mst.c */
 int intel_dp_mst_encoder_init(struct intel_digital_port *intel_dig_port, int conn_id);