drm/i915/tgl: add support to one DP-MST stream

This is the minimum change to support 1 (and only 1) DP-MST monitor
connected on Tiger Lake. This change was isolated from previous patch
from José. In order to support more streams we will need to create a
master-slave relation on the transcoders and that is not currently
working yet.

v2: remove unused macro and use REG_FIELD_PREP() (Ville)
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191029035049.5907-1-lucas.demarchi@intel.com

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

@@ -1905,6 +1905,9 @@ intel_ddi_transcoder_func_reg_val_get(const struct intel_crtc_state *crtc_state)
 	} else if (intel_crtc_has_type(crtc_state, INTEL_OUTPUT_DP_MST)) {
 		temp |= TRANS_DDI_MODE_SELECT_DP_MST;
 		temp |= DDI_PORT_WIDTH(crtc_state->lane_count);
+
+		if (INTEL_GEN(dev_priv) >= 12)
+			temp |= TRANS_DDI_MST_TRANSPORT_SELECT(crtc_state->cpu_transcoder);
 	} else {
 		temp |= TRANS_DDI_MODE_SELECT_DP_SST;
 		temp |= DDI_PORT_WIDTH(crtc_state->lane_count);

drivers/gpu/drm/i915/i915_reg.h

@@ -9657,6 +9657,9 @@ enum skl_power_gate {
 #define  TRANS_DDI_EDP_INPUT_A_ONOFF	(4 << 12)
 #define  TRANS_DDI_EDP_INPUT_B_ONOFF	(5 << 12)
 #define  TRANS_DDI_EDP_INPUT_C_ONOFF	(6 << 12)
+#define  TRANS_DDI_MST_TRANSPORT_SELECT_MASK	REG_GENMASK(12, 10)
+#define  TRANS_DDI_MST_TRANSPORT_SELECT(trans)	\
+	REG_FIELD_PREP(TRANS_DDI_MST_TRANSPORT_SELECT_MASK, trans)
 #define  TRANS_DDI_HDCP_SIGNALLING	(1 << 9)
 #define  TRANS_DDI_DP_VC_PAYLOAD_ALLOC	(1 << 8)
 #define  TRANS_DDI_HDMI_SCRAMBLER_CTS_ENABLE (1 << 7)