drm/amd/display: Fix dynamic link encoder access.

[Why]
Assuming DIG link encoders are statically mapped to links can cause
system instability due to null pointer accesses.

[How]
- Add checks for non-null link encoder pointers before trying to access
them.
- When a hardware platform uses dynamic DIG assignment (i.e. resource
function 'link_encs_assign' defined) and a link supports flexible
mapping to DIGs, use the link_enc_cfg API to access the DIG assigned to
a link or stream.

Reviewed-by: Meenakshikumar Somasundaram <meenakshikumar.somasundaram@amd.com>
Acked-by: Mikita Lipski <mikita.lipski@amd.com>
Signed-off-by: Jimmy Kizito <Jimmy.Kizito@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

1 files changed, 19 insertions, 1 deletions

diff --git a/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_resource.c b/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_resource.c
index 7bab88356df4..e69f553d680f 100644
--- a/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_resource.c
+++ b/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_resource.c
@@ -87,6 +87,7 @@
 #include "dce/dce_aux.h"
 #include "dce/dce_i2c.h"
 #include "vm_helper.h"
+#include "link_enc_cfg.h"
 
 #include "amdgpu_socbb.h"
 
@@ -1596,12 +1597,29 @@ static void get_pixel_clock_parameters(
 	const struct dc_stream_state *stream = pipe_ctx->stream;
 	struct pipe_ctx *odm_pipe;
 	int opp_cnt = 1;
+	struct dc_link *link = stream->link;
+	struct link_encoder *link_enc = NULL;
 
 	for (odm_pipe = pipe_ctx->next_odm_pipe; odm_pipe; odm_pipe = odm_pipe->next_odm_pipe)
 		opp_cnt++;
 
 	pixel_clk_params->requested_pix_clk_100hz = stream->timing.pix_clk_100hz;
-	pixel_clk_params->encoder_object_id = stream->link->link_enc->id;
+
+	/* 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->link->dc->current_state, stream);
+		if (link_enc == NULL)
+			link_enc = link_enc_cfg_get_next_avail_link_enc(stream->link->dc,
+				stream->link->dc->current_state);
+	} else
+		link_enc = stream->link->link_enc;
+	ASSERT(link_enc);
+
+	if (link_enc)
+		pixel_clk_params->encoder_object_id = link_enc->id;
 	pixel_clk_params->signal_type = pipe_ctx->stream->signal;
 	pixel_clk_params->controller_id = pipe_ctx->stream_res.tg->inst + 1;
 	/* TODO: un-hardcode*/