drm/amd/display: Fix detection of 4 lane for DPALT

[Why]
DPALT detection for B0 PHY has its own set of RDPCSPIPE registers

[How]
Use RDPCSPIPE registers to detect if DPALT lane is 4 lane
Reviewed-by: NCharlene Liu <Charlene.Liu@amd.com>
Acked-by: NSolomon Chiu <solomon.chiu@amd.com>
Signed-off-by: NHansen <Hansen.Dsouza@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dcn31/dcn31_dio_link_encoder.c

@@ -63,6 +63,10 @@
 #define AUX_REG_WRITE(reg_name, val) \
 			dm_write_reg(CTX, AUX_REG(reg_name), val)
 
+#ifndef MIN
+#define MIN(X, Y) ((X) < (Y) ? (X) : (Y))
+#endif
+
 void dcn31_link_encoder_set_dio_phy_mux(
 	struct link_encoder *enc,
 	enum encoder_type_select sel,
@@ -217,7 +221,7 @@ static const struct link_encoder_funcs dcn31_link_enc_funcs = {
 	.get_dig_frontend = dcn10_get_dig_frontend,
 	.get_dig_mode = dcn10_get_dig_mode,
 	.is_in_alt_mode = dcn31_link_encoder_is_in_alt_mode,
-	.get_max_link_cap = dcn20_link_encoder_get_max_link_cap,
+	.get_max_link_cap = dcn31_link_encoder_get_max_link_cap,
 	.set_dio_phy_mux = dcn31_link_encoder_set_dio_phy_mux,
 };
 
@@ -439,3 +443,30 @@ bool dcn31_link_encoder_is_in_alt_mode(struct link_encoder *enc)
 
 	return is_usb_c_alt_mode;
 }
+
+void dcn31_link_encoder_get_max_link_cap(struct link_encoder *enc,
+										 struct dc_link_settings *link_settings)
+{
+	struct dcn10_link_encoder *enc10 = TO_DCN10_LINK_ENC(enc);
+	uint32_t is_in_usb_c_dp4_mode = 0;
+
+	dcn10_link_encoder_get_max_link_cap(enc, link_settings);
+
+	/* in usb c dp2 mode, max lane count is 2 */
+	if (enc->funcs->is_in_alt_mode && enc->funcs->is_in_alt_mode(enc)) {
+		if (enc->ctx->asic_id.hw_internal_rev != YELLOW_CARP_B0) {
+			// [Note] no need to check hw_internal_rev once phy mux selection is ready
+			REG_GET(RDPCSTX_PHY_CNTL6, RDPCS_PHY_DPALT_DP4, &is_in_usb_c_dp4_mode);
+		} else {
+			if ((enc10->base.transmitter == TRANSMITTER_UNIPHY_A)
+					|| (enc10->base.transmitter == TRANSMITTER_UNIPHY_B)
+					|| (enc10->base.transmitter == TRANSMITTER_UNIPHY_E)) {
+				REG_GET(RDPCSTX_PHY_CNTL6, RDPCS_PHY_DPALT_DP4, &is_in_usb_c_dp4_mode);
+			} else {
+				REG_GET(RDPCSPIPE_PHY_CNTL6, RDPCS_PHY_DPALT_DP4, &is_in_usb_c_dp4_mode);
+			}
+		}
+		if (!is_in_usb_c_dp4_mode)
+			link_settings->lane_count = MIN(LANE_COUNT_TWO, link_settings->lane_count);
+	}
+}

drivers/gpu/drm/amd/display/dc/dcn31/dcn31_dio_link_encoder.h

@@ -252,4 +252,7 @@ void dcn31_link_encoder_disable_output(
 bool dcn31_link_encoder_is_in_alt_mode(
 	struct link_encoder *enc);
 
+void dcn31_link_encoder_get_max_link_cap(struct link_encoder *enc,
+	struct dc_link_settings *link_settings);
+
 #endif /* __DC_LINK_ENCODER__DCN31_H__ */