drm/i915/ddi: handle 128b/132b SST in intel_ddi_read_func_ctl()

We'll only ever get here in MST mode from MST stream encoders; the
primary encoder's ->get_config() won't be called when we've detected
it's MST.

v2: Read mst_master_transcoder in 128b/132b SST path (Imre)

Reviewed-by: Imre Deak <[e-mail]>
Signed-off-by: Jani Nikula <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/436[e-mail]

drivers/gpu/drm/i915/display/intel_ddi.c

···
 	crtc_state->lane_count =
 		((ddi_func_ctl & DDI_PORT_WIDTH_MASK) >> DDI_PORT_WIDTH_SHIFT) + 1;
 
+	if (DISPLAY_VER(display) >= 12 &&
+	    (ddi_func_ctl & TRANS_DDI_MODE_SELECT_MASK) == TRANS_DDI_MODE_SELECT_FDI_OR_128B132B)
+		crtc_state->mst_master_transcoder =
+			REG_FIELD_GET(TRANS_DDI_MST_TRANSPORT_SELECT_MASK, ddi_func_ctl);
+
 	intel_cpu_transcoder_get_m1_n1(crtc, cpu_transcoder, &crtc_state->dp_m_n);
 	intel_cpu_transcoder_get_m2_n2(crtc, cpu_transcoder, &crtc_state->dp_m2_n2);
 
···
 		intel_ddi_read_func_ctl_fdi(encoder, pipe_config, ddi_func_ctl);
 	} else if (ddi_mode == TRANS_DDI_MODE_SELECT_DP_SST) {
 		intel_ddi_read_func_ctl_dp_sst(encoder, pipe_config, ddi_func_ctl);
-	} else if (ddi_mode == TRANS_DDI_MODE_SELECT_DP_MST ||
-		   (ddi_mode == TRANS_DDI_MODE_SELECT_FDI_OR_128B132B && HAS_DP20(display))) {
+	} else if (ddi_mode == TRANS_DDI_MODE_SELECT_DP_MST) {
 		intel_ddi_read_func_ctl_dp_mst(encoder, pipe_config, ddi_func_ctl);
+	} else if (ddi_mode == TRANS_DDI_MODE_SELECT_FDI_OR_128B132B && HAS_DP20(display)) {
+		struct intel_dp *intel_dp = enc_to_intel_dp(encoder);
+
+		/*
+		 * If this is true, we know we're being called from mst stream
+		 * encoder's ->get_config().
+		 */
+		if (intel_dp->is_mst)
+			intel_ddi_read_func_ctl_dp_mst(encoder, pipe_config, ddi_func_ctl);
+		else
+			intel_ddi_read_func_ctl_dp_sst(encoder, pipe_config, ddi_func_ctl);
 	}
 }