drm/i915: Support DP MST in enc_to_dig_port() function

Although DP_MST fake encoders are not subclassed from digital ports,
they are associated with them. Support these encoders.
Reviewed-by: Ramalingam C <ramalingam.c@intel.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20191203173638.94919-9-sean@poorly.run #v1
Link: https://patchwork.freedesktop.org/patch/msgid/20191212190230.188505-10-sean@poorly.run #v2
Link: https://patchwork.freedesktop.org/patch/msgid/20200117193103.156821-10-sean@poorly.run #v3
Link: https://patchwork.freedesktop.org/patch/msgid/20200218220242.107265-10-sean@poorly.run #v4
Link: https://patchwork.freedesktop.org/patch/msgid/20200305201236.152307-10-sean@poorly.run #v5
Link: https://patchwork.freedesktop.org/patch/msgid/20200429195502.39919-10-sean@poorly.run #v6
Link: https://patchwork.freedesktop.org/patch/msgid/20200623155907.22961-11-sean@poorly.run #v7

Changes in v2:
-None
Changes in v3:
-None
Changes in v4:
-None
Changes in v5:
-None
Changes in v6:
-None
Changes in v7:
-None
Changes in v8:
-None
Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200818153910.27894-11-sean@poorly.run

drivers/gpu/drm/i915/display/intel_display_types.h

@@ -1531,6 +1531,18 @@ static inline bool intel_encoder_is_dig_port(struct intel_encoder *encoder)
 	}
 }
 
+static inline bool intel_encoder_is_mst(struct intel_encoder *encoder)
+{
+	return encoder->type == INTEL_OUTPUT_DP_MST;
+}
+
+static inline struct intel_dp_mst_encoder *
+enc_to_mst(struct intel_encoder *encoder)
+{
+	return container_of(&encoder->base, struct intel_dp_mst_encoder,
+			    base.base);
+}
+
 static inline struct intel_digital_port *
 enc_to_dig_port(struct intel_encoder *encoder)
 {
@@ -1539,6 +1551,8 @@ enc_to_dig_port(struct intel_encoder *encoder)
 	if (intel_encoder_is_dig_port(intel_encoder))
 		return container_of(&encoder->base, struct intel_digital_port,
 				    base.base);
+	else if (intel_encoder_is_mst(intel_encoder))
+		return enc_to_mst(encoder)->primary;
 	else
 		return NULL;
 }
@@ -1549,13 +1563,6 @@ intel_attached_dig_port(struct intel_connector *connector)
 	return enc_to_dig_port(intel_attached_encoder(connector));
 }
 
-static inline struct intel_dp_mst_encoder *
-enc_to_mst(struct intel_encoder *encoder)
-{
-	return container_of(&encoder->base, struct intel_dp_mst_encoder,
-			    base.base);
-}
-
 static inline struct intel_dp *enc_to_intel_dp(struct intel_encoder *encoder)
 {
 	return &enc_to_dig_port(encoder)->dp;