drm/i915/dp: Configure Display stream splitter registers during DSC enable

Display Stream Splitter registers need to be programmed to enable
the joiner if two DSC engines are used and also to enable
the left and the right DSC engines. This happens as part of
the DSC enabling routine in the source in atomic commit.

v4:
* Remove redundant comment (Ville)
v3:
* Use cpu_transcoder instead of encoder->type (Ville)
v2:
* Rebase (Manasi)

Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Cc: Anusha Srivatsa <anusha.srivatsa@intel.com>
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Reviewed-by: Anusha Srivatsa <anusha.srivatsa@intelcom>
Link: https://patchwork.freedesktop.org/patch/msgid/20181128202628.20238-11-manasi.d.navare@intel.com

drivers/gpu/drm/i915/intel_vdsc.c

@@ -1000,10 +1000,32 @@ static void intel_dp_write_dsc_pps_sdp(struct intel_encoder *encoder,
 void intel_dsc_enable(struct intel_encoder *encoder,
 		      const struct intel_crtc_state *crtc_state)
 {
+	struct intel_crtc *crtc = to_intel_crtc(crtc_state->base.crtc);
+	struct drm_i915_private *dev_priv = to_i915(encoder->base.dev);
+	enum pipe pipe = crtc->pipe;
+	i915_reg_t dss_ctl1_reg, dss_ctl2_reg;
+	u32 dss_ctl1_val = 0;
+	u32 dss_ctl2_val = 0;
+
 	if (!crtc_state->dsc_params.compression_enable)
 		return;
 
 	intel_configure_pps_for_dsc_encoder(encoder, crtc_state);
 
 	intel_dp_write_dsc_pps_sdp(encoder, crtc_state);
+
+	if (crtc_state->cpu_transcoder == TRANSCODER_EDP) {
+		dss_ctl1_reg = DSS_CTL1;
+		dss_ctl2_reg = DSS_CTL2;
+	} else {
+		dss_ctl1_reg = ICL_PIPE_DSS_CTL1(pipe);
+		dss_ctl2_reg = ICL_PIPE_DSS_CTL2(pipe);
+	}
+	dss_ctl2_val |= LEFT_BRANCH_VDSC_ENABLE;
+	if (crtc_state->dsc_params.dsc_split) {
+		dss_ctl2_val |= RIGHT_BRANCH_VDSC_ENABLE;
+		dss_ctl1_val |= JOINER_ENABLE;
+	}
+	I915_WRITE(dss_ctl1_reg, dss_ctl1_val);
+	I915_WRITE(dss_ctl2_reg, dss_ctl2_val);
 }