drm/amd/display: handle null link encoder

[Why]
The link encoder mapping could return a null one and causes system crash.

[How]
Let the mapping can get an available link encoder without endpoint
identification check.
Reviewed-by: Wenjing Liu <Wenjing.Liu@amd.com>
Acked-by: Jasdeep Dhillon <jdhillon@amd.com>
Signed-off-by: Martin Tsai <martin.tsai@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -3530,11 +3530,7 @@ enum dc_status dc_link_allocate_mst_payload(struct pipe_ctx *pipe_ctx)
 	const struct link_hwss *link_hwss = get_link_hwss(link, &pipe_ctx->link_res);
 	DC_LOGGER_INIT(link->ctx->logger);
 
-	/* Link encoder may have been dynamically assigned to non-physical display endpoint. */
-	if (link->ep_type == DISPLAY_ENDPOINT_PHY)
-		link_encoder = link->link_enc;
-	else if (link->dc->res_pool->funcs->link_encs_assign)
-		link_encoder = link_enc_cfg_get_link_enc_used_by_stream(pipe_ctx->stream->ctx->dc, stream);
+	link_encoder = link_enc_cfg_get_link_enc(link);
 	ASSERT(link_encoder);
 
 	/* enable_link_dp_mst already check link->enabled_stream_count
@@ -3823,11 +3819,7 @@ static enum dc_status deallocate_mst_payload(struct pipe_ctx *pipe_ctx)
 	const struct dc_link_settings empty_link_settings = {0};
 	DC_LOGGER_INIT(link->ctx->logger);
 
-	/* Link encoder may have been dynamically assigned to non-physical display endpoint. */
-	if (link->ep_type == DISPLAY_ENDPOINT_PHY)
-		link_encoder = link->link_enc;
-	else if (link->dc->res_pool->funcs->link_encs_assign)
-		link_encoder = link_enc_cfg_get_link_enc_used_by_stream(pipe_ctx->stream->ctx->dc, stream);
+	link_encoder = link_enc_cfg_get_link_enc(link);
 	ASSERT(link_encoder);
 
 	/* deallocate_mst_payload is called before disable link. When mode or
@@ -3944,13 +3936,7 @@ static void update_psp_stream_config(struct pipe_ctx *pipe_ctx, bool dpms_off)
 	if (cp_psp == NULL || cp_psp->funcs.update_stream_config == NULL)
 		return;
 
-	if (pipe_ctx->stream->link->ep_type == DISPLAY_ENDPOINT_PHY)
-		link_enc = pipe_ctx->stream->link->link_enc;
-	else if (pipe_ctx->stream->link->ep_type == DISPLAY_ENDPOINT_USB4_DPIA &&
-			pipe_ctx->stream->link->dc->res_pool->funcs->link_encs_assign)
-		link_enc = link_enc_cfg_get_link_enc_used_by_stream(
-				pipe_ctx->stream->ctx->dc,
-				pipe_ctx->stream);
+	link_enc = link_enc_cfg_get_link_enc(pipe_ctx->stream->link);
 	ASSERT(link_enc);
 	if (link_enc == NULL)
 		return;
@@ -4100,10 +4086,7 @@ void core_link_enable_stream(
 			dc_is_virtual_signal(pipe_ctx->stream->signal))
 		return;
 
-	if (dc->res_pool->funcs->link_encs_assign && stream->link->ep_type != DISPLAY_ENDPOINT_PHY)
-		link_enc = link_enc_cfg_get_link_enc_used_by_stream(dc, stream);
-	else
-		link_enc = stream->link->link_enc;
+	link_enc = link_enc_cfg_get_link_enc(link);
 	ASSERT(link_enc);
 
 	if (!dc_is_virtual_signal(pipe_ctx->stream->signal)

drivers/gpu/drm/amd/display/dc/dcn20/dcn20_resource.c

@@ -1605,16 +1605,7 @@ static void get_pixel_clock_parameters(
 
 	pixel_clk_params->requested_pix_clk_100hz = stream->timing.pix_clk_100hz;
 
-	/* Links supporting dynamically assigned link encoder will be assigned next
-	 * available encoder if one not already assigned.
-	 */
-	if (link->is_dig_mapping_flexible &&
-			link->dc->res_pool->funcs->link_encs_assign) {
-		link_enc = link_enc_cfg_get_link_enc_used_by_stream(stream->ctx->dc, stream);
-		if (link_enc == NULL)
-			link_enc = link_enc_cfg_get_next_avail_link_enc(stream->ctx->dc);
-	} else
-		link_enc = stream->link->link_enc;
+	link_enc = link_enc_cfg_get_link_enc(link);
 	ASSERT(link_enc);
 
 	if (link_enc)