drm/amd/display: add helper for enabling mst stream features

[Why]
Some MST devices uses different method to enable mst
specific stream features.

[How]
Add dm_helpers_mst_enable_stream features. This can be
modified later when we are ready to implement those features.
Signed-off-by: Bing Guo <bing.guo@amd.com>
Reviewed-by: Anthony Koo <Anthony.Koo@amd.com>
Acked-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c

@@ -711,3 +711,28 @@ bool dm_helpers_dmub_outbox0_interrupt_control(struct dc_context *ctx, bool enab
 			 enable ? "en" : "dis", ret);
 	return ret;
 }
+
+void dm_helpers_mst_enable_stream_features(const struct dc_stream_state *stream)
+{
+	/* TODO: virtual DPCD */
+	struct dc_link *link = stream->link;
+	union down_spread_ctrl old_downspread;
+	union down_spread_ctrl new_downspread;
+
+	if (link->aux_access_disabled)
+		return;
+
+	if (!dm_helpers_dp_read_dpcd(link->ctx, link, DP_DOWNSPREAD_CTRL,
+				     &old_downspread.raw,
+				     sizeof(old_downspread)))
+		return;
+
+	new_downspread.raw = old_downspread.raw;
+	new_downspread.bits.IGNORE_MSA_TIMING_PARAM =
+		(stream->ignore_msa_timing_param) ? 1 : 0;
+
+	if (new_downspread.raw != old_downspread.raw)
+		dm_helpers_dp_write_dpcd(link->ctx, link, DP_DOWNSPREAD_CTRL,
+					 &new_downspread.raw,
+					 sizeof(new_downspread));
+}

drivers/gpu/drm/amd/display/dc/core/dc_link.c

@@ -1679,6 +1679,8 @@ void link_destroy(struct dc_link **link)
 static void enable_stream_features(struct pipe_ctx *pipe_ctx)
 {
 	struct dc_stream_state *stream = pipe_ctx->stream;
+
+	if (pipe_ctx->stream->signal != SIGNAL_TYPE_DISPLAY_PORT_MST) {
 		struct dc_link *link = stream->link;
 		union down_spread_ctrl old_downspread;
 		union down_spread_ctrl new_downspread;
@@ -1695,6 +1697,10 @@ static void enable_stream_features(struct pipe_ctx *pipe_ctx)
 			core_link_write_dpcd(link, DP_DOWNSPREAD_CTRL,
 				&new_downspread.raw, sizeof(new_downspread));
 		}
+
+	} else {
+		dm_helpers_mst_enable_stream_features(stream);
+	}
 }
 
 static enum dc_status enable_link_dp(struct dc_state *state,

drivers/gpu/drm/amd/display/dc/dm_helpers.h

@@ -147,6 +147,8 @@ bool dm_helpers_dp_write_dsc_enable(
 bool dm_helpers_is_dp_sink_present(
 		struct dc_link *link);
 
+void dm_helpers_mst_enable_stream_features(const struct dc_stream_state *stream);
+
 enum dc_edid_status dm_helpers_read_local_edid(
 		struct dc_context *ctx,
 		struct dc_link *link,