diff mbox series

[25/30] drm/amd/display: Fix dynamic link encoder access.

Message ID 20211122180632.72792-29-tjaalton@ubuntu.com
State New
Headers show
Series drm/amdgpu: Add USB4 support for DP tunneling | expand

Commit Message

Timo Aaltonen Nov. 22, 2021, 6:06 p.m. UTC
From: Jimmy Kizito <Jimmy.Kizito@amd.com>

BugLink: https://bugs.launchpad.net/bugs/1951868

[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>
(backported from commit 64d283cb379eadcb412ebba3b61808b58d0c6193 - fix conflicts in dc_link.c, dc-link_dp.c, dce110_hw_sequencer.c, dcn20_hwseq.c, dcn31_hwseq.c)
Signed-off-by: Timo Aaltonen <timo.aaltonen@canonical.com>
---
 .../display/dc/clk_mgr/dcn31/dcn31_clk_mgr.c  |  2 +-
 drivers/gpu/drm/amd/display/dc/core/dc_link.c | 36 ++++++++++++++-----
 .../gpu/drm/amd/display/dc/core/dc_link_dp.c  | 36 ++++++++++++++++---
 .../drm/amd/display/dc/core/dc_link_enc_cfg.c | 25 +++++++------
 .../drm/amd/display/dc/core/dc_link_hwss.c    |  7 ++--
 .../gpu/drm/amd/display/dc/core/dc_resource.c |  3 +-
 .../display/dc/dce110/dce110_hw_sequencer.c   | 10 ++++--
 .../drm/amd/display/dc/dcn10/dcn10_resource.c |  2 +-
 .../drm/amd/display/dc/dcn20/dcn20_hwseq.c    |  7 ++++
 .../drm/amd/display/dc/dcn20/dcn20_resource.c | 20 ++++++++++-
 .../drm/amd/display/dc/dcn31/dcn31_hwseq.c    |  6 +++-
 .../gpu/drm/amd/display/dc/inc/link_enc_cfg.h |  5 +++
 12 files changed, 126 insertions(+), 33 deletions(-)
diff mbox series

Patch

diff --git a/drivers/gpu/drm/amd/display/dc/clk_mgr/dcn31/dcn31_clk_mgr.c b/drivers/gpu/drm/amd/display/dc/clk_mgr/dcn31/dcn31_clk_mgr.c
index 377c4e53a2b3..3378e1695d13 100644
--- a/drivers/gpu/drm/amd/display/dc/clk_mgr/dcn31/dcn31_clk_mgr.c
+++ b/drivers/gpu/drm/amd/display/dc/clk_mgr/dcn31/dcn31_clk_mgr.c
@@ -87,7 +87,7 @@  int dcn31_get_active_display_cnt_wa(
 		const struct dc_link *link = dc->links[i];
 
 		/* abusing the fact that the dig and phy are coupled to see if the phy is enabled */
-		if (link->link_enc->funcs->is_dig_enabled &&
+		if (link->link_enc && link->link_enc->funcs->is_dig_enabled &&
 				link->link_enc->funcs->is_dig_enabled(link->link_enc))
 			display_count++;
 	}
diff --git a/drivers/gpu/drm/amd/display/dc/core/dc_link.c b/drivers/gpu/drm/amd/display/dc/core/dc_link.c
index 43971f3759eb..342a8adb94ee 100644
--- a/drivers/gpu/drm/amd/display/dc/core/dc_link.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc_link.c
@@ -3320,6 +3320,10 @@  static enum dc_status deallocate_mst_payload(struct pipe_ctx *pipe_ctx)
 static void update_psp_stream_config(struct pipe_ctx *pipe_ctx, bool dpms_off)
 {
 	struct cp_psp *cp_psp = &pipe_ctx->stream->ctx->cp_psp;
+#if defined(CONFIG_DRM_AMD_DC_DCN)
+	struct link_encoder *link_enc = NULL;
+#endif
+
 	if (cp_psp && cp_psp->funcs.update_stream_config) {
 		struct cp_psp_stream_config config = {0};
 		enum dp_panel_mode panel_mode =
@@ -3331,8 +3335,21 @@  static void update_psp_stream_config(struct pipe_ctx *pipe_ctx, bool dpms_off)
 		config.dig_be = pipe_ctx->stream->link->link_enc_hw_inst;
 #if defined(CONFIG_DRM_AMD_DC_DCN)
 		config.stream_enc_idx = pipe_ctx->stream_res.stream_enc->id - ENGINE_ID_DIGA;
-		config.link_enc_idx = pipe_ctx->stream->link->link_enc->transmitter - TRANSMITTER_UNIPHY_A;
-		config.phy_idx = pipe_ctx->stream->link->link_enc->transmitter - TRANSMITTER_UNIPHY_A;
+		if (pipe_ctx->stream->link->ep_type == DISPLAY_ENDPOINT_PHY) {
+			link_enc = pipe_ctx->stream->link->link_enc;
+			config.phy_idx = link_enc->transmitter - TRANSMITTER_UNIPHY_A;
+		} else if (pipe_ctx->stream->link->dc->res_pool->funcs->link_encs_assign) {
+			/* Use link encoder assignment from current DC state - which may differ from the DC state to be
+			 * committed - when updating PSP config.
+			 */
+			link_enc = link_enc_cfg_get_link_enc_used_by_stream(
+					pipe_ctx->stream->link->dc->current_state,
+					pipe_ctx->stream);
+			config.phy_idx = 0; /* Clear phy_idx for non-physical display endpoints. */
+		}
+		ASSERT(link_enc);
+		if (link_enc)
+			config.link_enc_idx = link_enc->transmitter - TRANSMITTER_UNIPHY_A;
 #endif
 		config.dpms_off = dpms_off;
 		config.dm_stream_ctx = pipe_ctx->stream->dm_stream_context;
@@ -3352,6 +3369,7 @@  void core_link_enable_stream(
 	struct dc_stream_state *stream = pipe_ctx->stream;
 	struct dc_link *link = stream->sink->link;
 	enum dc_status status;
+	struct link_encoder *link_enc;
 #if defined(CONFIG_DRM_AMD_DC_DCN)
 	enum otg_out_mux_dest otg_out_dest = OUT_MUX_DIO;
 #endif
@@ -3362,9 +3380,10 @@  void core_link_enable_stream(
 		return;
 
 	if (!dc_is_virtual_signal(pipe_ctx->stream->signal)) {
-		stream->link->link_enc->funcs->setup(
-			stream->link->link_enc,
-			pipe_ctx->stream->signal);
+		if (link_enc)
+			link_enc->funcs->setup(
+				link_enc,
+				pipe_ctx->stream->signal);
 		pipe_ctx->stream_res.stream_enc->funcs->setup_stereo_sync(
 			pipe_ctx->stream_res.stream_enc,
 			pipe_ctx->stream_res.tg->inst,
@@ -3495,9 +3514,10 @@  void core_link_enable_stream(
 		 * from transmitter control.
 		 */
 		if (!dc_is_virtual_signal(pipe_ctx->stream->signal))
-			stream->link->link_enc->funcs->setup(
-				stream->link->link_enc,
-				pipe_ctx->stream->signal);
+			if (link_enc)
+				link_enc->funcs->setup(
+					link_enc,
+					pipe_ctx->stream->signal);
 
 		dc->hwss.enable_stream(pipe_ctx);
 
diff --git a/drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c b/drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c
index 299ab7b92cb6..607285c0c3cd 100644
--- a/drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c
@@ -2055,13 +2055,27 @@  bool dc_link_dp_sync_lt_end(struct dc_link *link, bool link_down)
 
 bool dc_link_dp_get_max_link_enc_cap(const struct dc_link *link, struct dc_link_settings *max_link_enc_cap)
 {
+	struct link_encoder *link_enc = NULL;
+
 	if (!max_link_enc_cap) {
 		DC_LOG_ERROR("%s: Could not return max link encoder caps", __func__);
 		return false;
 	}
 
-	if (link->link_enc->funcs->get_max_link_cap) {
-		link->link_enc->funcs->get_max_link_cap(link->link_enc, max_link_enc_cap);
+	/* 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_link(link->dc->current_state, link);
+		if (link_enc == NULL)
+			link_enc = link_enc_cfg_get_next_avail_link_enc(link->dc, link->dc->current_state);
+	} else
+		link_enc = link->link_enc;
+	ASSERT(link_enc);
+
+	if (link_enc && link_enc->funcs->get_max_link_cap) {
+		link_enc->funcs->get_max_link_cap(link_enc, max_link_enc_cap);
 		return true;
 	}
 
@@ -2074,9 +2088,23 @@  bool dc_link_dp_get_max_link_enc_cap(const struct dc_link *link, struct dc_link_
 static struct dc_link_settings get_max_link_cap(struct dc_link *link)
 {
 	struct dc_link_settings max_link_cap = {0};
+	struct link_encoder *link_enc = NULL;
+
+	/* 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_link(link->dc->current_state, link);
+		if (link_enc == NULL)
+			link_enc = link_enc_cfg_get_next_avail_link_enc(link->dc, link->dc->current_state);
+	} else
+		link_enc = link->link_enc;
+	ASSERT(link_enc);
 
 	/* get max link encoder capability */
-	link->link_enc->funcs->get_max_link_cap(link->link_enc, &max_link_cap);
+	if (link_enc)
+		link_enc->funcs->get_max_link_cap(link_enc, &max_link_cap);
 
 	/* Lower link settings based on sink's link cap */
 	if (link->reported_link_cap.lane_count < max_link_cap.lane_count)
@@ -2279,7 +2307,7 @@  bool dp_verify_link_cap(
 	 * PHY will sometimes be in bad state on hotplugging display from certain USB-C dongle,
 	 * so add extra cycle of enabling and disabling the PHY before first link training.
 	 */
-	if (link->link_enc->features.flags.bits.DP_IS_USB_C &&
+	if (link->link_enc && link->link_enc->features.flags.bits.DP_IS_USB_C &&
 			link->dc->debug.usbc_combo_phy_reset_wa) {
 		dp_enable_link_phy(link, link->connector_signal, dp_cs_id, cur);
 		dp_disable_link_phy(link, link->connector_signal);
diff --git a/drivers/gpu/drm/amd/display/dc/core/dc_link_enc_cfg.c b/drivers/gpu/drm/amd/display/dc/core/dc_link_enc_cfg.c
index de80a9ea4cfa..49b17bbea8d1 100644
--- a/drivers/gpu/drm/amd/display/dc/core/dc_link_enc_cfg.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc_link_enc_cfg.c
@@ -139,7 +139,7 @@  static struct dc_stream_state *get_stream_using_link_enc(
 	for (i = 0; i < state->stream_count; i++) {
 		struct link_enc_assignment assignment = state->res_ctx.link_enc_assignments[i];
 
-		if (assignment.valid && (assignment.eng_id == eng_id)) {
+		if ((assignment.valid == true) && (assignment.eng_id == eng_id)) {
 			stream_idx = i;
 			break;
 		}
@@ -254,7 +254,7 @@  struct dc_link *link_enc_cfg_get_link_using_link_enc(
 	for (i = 0; i < state->stream_count; i++) {
 		struct link_enc_assignment assignment = state->res_ctx.link_enc_assignments[i];
 
-		if (assignment.valid && (assignment.eng_id == eng_id)) {
+		if ((assignment.valid == true) && (assignment.eng_id == eng_id)) {
 			stream_idx = i;
 			break;
 		}
@@ -274,7 +274,6 @@  struct link_encoder *link_enc_cfg_get_link_enc_used_by_link(
 {
 	struct link_encoder *link_enc = NULL;
 	struct display_endpoint_id ep_id;
-	int stream_idx = -1;
 	int i;
 
 	ep_id = (struct display_endpoint_id) {
@@ -283,20 +282,15 @@  struct link_encoder *link_enc_cfg_get_link_enc_used_by_link(
 
 	for (i = 0; i < state->stream_count; i++) {
 		struct link_enc_assignment assignment = state->res_ctx.link_enc_assignments[i];
-
-		if (assignment.valid &&
+		if (assignment.valid == true &&
 				assignment.ep_id.link_id.id == ep_id.link_id.id &&
 				assignment.ep_id.link_id.enum_id == ep_id.link_id.enum_id &&
 				assignment.ep_id.link_id.type == ep_id.link_id.type &&
 				assignment.ep_id.ep_type == ep_id.ep_type) {
-			stream_idx = i;
-			break;
+			link_enc = link->dc->res_pool->link_encoders[assignment.eng_id - ENGINE_ID_DIGA];
 		}
 	}
 
-	if (stream_idx != -1)
-		link_enc = state->streams[stream_idx]->link_enc;
-
 	return link_enc;
 }
 
@@ -313,3 +307,14 @@  struct link_encoder *link_enc_cfg_get_next_avail_link_enc(
 
 	return link_enc;
 }
+
+struct link_encoder *link_enc_cfg_get_link_enc_used_by_stream(
+		struct dc_state *state,
+		const struct dc_stream_state *stream)
+{
+	struct link_encoder *link_enc;
+
+	link_enc = link_enc_cfg_get_link_enc_used_by_link(state, stream->link);
+
+	return link_enc;
+}
diff --git a/drivers/gpu/drm/amd/display/dc/core/dc_link_hwss.c b/drivers/gpu/drm/amd/display/dc/core/dc_link_hwss.c
index 2a064f7b669e..4ca1002c9d01 100644
--- a/drivers/gpu/drm/amd/display/dc/core/dc_link_hwss.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc_link_hwss.c
@@ -362,9 +362,10 @@  void dp_retrain_link_dp_test(struct dc_link *link,
 			if ((&pipes[i])->stream_res.audio && !link->dc->debug.az_endpoint_mute_only)
 				(&pipes[i])->stream_res.audio->funcs->az_disable((&pipes[i])->stream_res.audio);
 
-			link->link_enc->funcs->disable_output(
-					link->link_enc,
-					SIGNAL_TYPE_DISPLAY_PORT);
+			if (link->link_enc)
+				link->link_enc->funcs->disable_output(
+						link->link_enc,
+						SIGNAL_TYPE_DISPLAY_PORT);
 
 			/* Clear current link setting. */
 			memset(&link->cur_link_settings, 0,
diff --git a/drivers/gpu/drm/amd/display/dc/core/dc_resource.c b/drivers/gpu/drm/amd/display/dc/core/dc_resource.c
index a60396d5be44..82981a1845c7 100644
--- a/drivers/gpu/drm/amd/display/dc/core/dc_resource.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc_resource.c
@@ -2871,7 +2871,8 @@  enum dc_status dc_validate_stream(struct dc *dc, struct dc_stream_state *stream)
 		res = DC_FAIL_CONTROLLER_VALIDATE;
 
 	if (res == DC_OK) {
-		if (!link->link_enc->funcs->validate_output_with_stream(
+		if (link->ep_type == DISPLAY_ENDPOINT_PHY &&
+				!link->link_enc->funcs->validate_output_with_stream(
 						link->link_enc, stream))
 			res = DC_FAIL_ENC_VALIDATE;
 	}
diff --git a/drivers/gpu/drm/amd/display/dc/dce110/dce110_hw_sequencer.c b/drivers/gpu/drm/amd/display/dc/dce110/dce110_hw_sequencer.c
index db32b519f735..3234338bd086 100644
--- a/drivers/gpu/drm/amd/display/dc/dce110/dce110_hw_sequencer.c
+++ b/drivers/gpu/drm/amd/display/dc/dce110/dce110_hw_sequencer.c
@@ -46,6 +46,7 @@ 
 #include "transform.h"
 #include "stream_encoder.h"
 #include "link_encoder.h"
+#include "link_enc_cfg.h"
 #include "link_hwss.h"
 #include "dc_link_dp.h"
 #if defined(CONFIG_DRM_AMD_DC_DCN)
@@ -1165,6 +1166,7 @@  void dce110_disable_stream(struct pipe_ctx *pipe_ctx)
 	struct dc_stream_state *stream = pipe_ctx->stream;
 	struct dc_link *link = stream->link;
 	struct dc *dc = pipe_ctx->stream->ctx->dc;
+	struct link_encoder *link_enc = NULL;
 
 	if (dc_is_hdmi_tmds_signal(pipe_ctx->stream->signal)) {
 		pipe_ctx->stream_res.stream_enc->funcs->stop_hdmi_info_packets(
@@ -1179,7 +1181,8 @@  void dce110_disable_stream(struct pipe_ctx *pipe_ctx)
 
 	dc->hwss.disable_audio_stream(pipe_ctx);
 
-	link->link_enc->funcs->connect_dig_be_to_fe(
+	if (link_enc)
+		link_enc->funcs->connect_dig_be_to_fe(
 			link->link_enc,
 			pipe_ctx->stream_res.stream_enc->id,
 			false);
@@ -1560,8 +1563,9 @@  static void power_down_encoders(struct dc *dc)
 		if (signal != SIGNAL_TYPE_EDP)
 			signal = SIGNAL_TYPE_NONE;
 
-		dc->links[i]->link_enc->funcs->disable_output(
-				dc->links[i]->link_enc, signal);
+		if (dc->links[i]->ep_type == DISPLAY_ENDPOINT_PHY)
+			dc->links[i]->link_enc->funcs->disable_output(
+					dc->links[i]->link_enc, signal);
 
 		dc->links[i]->link_status.link_active = false;
 		memset(&dc->links[i]->cur_link_settings, 0,
diff --git a/drivers/gpu/drm/amd/display/dc/dcn10/dcn10_resource.c b/drivers/gpu/drm/amd/display/dc/dcn10/dcn10_resource.c
index 7daadb6a5233..f37551e00023 100644
--- a/drivers/gpu/drm/amd/display/dc/dcn10/dcn10_resource.c
+++ b/drivers/gpu/drm/amd/display/dc/dcn10/dcn10_resource.c
@@ -1296,7 +1296,7 @@  struct stream_encoder *dcn10_find_first_free_match_stream_enc_for_link(
 			 * in daisy chain use case
 			 */
 			j = i;
-			if (pool->stream_enc[i]->id ==
+			if (link->ep_type == DISPLAY_ENDPOINT_PHY && pool->stream_enc[i]->id ==
 					link->link_enc->preferred_engine)
 				return pool->stream_enc[i];
 		}
diff --git a/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_hwseq.c b/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_hwseq.c
index f15c1944bd1b..47cf2c14ab9a 100644
--- a/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_hwseq.c
+++ b/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_hwseq.c
@@ -2376,6 +2376,13 @@  void dcn20_enable_stream(struct pipe_ctx *pipe_ctx)
 	uint32_t active_total_with_borders;
 	uint32_t early_control = 0;
 	struct timing_generator *tg = pipe_ctx->stream_res.tg;
+	struct link_encoder *link_enc;
+
+	if (link->is_dig_mapping_flexible &&
+			link->dc->res_pool->funcs->link_encs_assign)
+		link_enc = pipe_ctx->stream->link_enc;
+	else
+		link_enc = link->link_enc;
 
 	/* For MST, there are multiply stream go to only one link.
 	 * connect DIG back_end to front_end while enable_stream and
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 e3e01b17c164..36a5c5c07c58 100644
--- a/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_resource.c
+++ b/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_resource.c
@@ -86,6 +86,7 @@ 
 #include "dce/dce_aux.h"
 #include "dce/dce_i2c.h"
 #include "vm_helper.h"
+#include "link_enc_cfg.h"
 
 #include "amdgpu_socbb.h"
 
@@ -1595,12 +1596,29 @@  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*/
diff --git a/drivers/gpu/drm/amd/display/dc/dcn31/dcn31_hwseq.c b/drivers/gpu/drm/amd/display/dc/dcn31/dcn31_hwseq.c
index d15bcc086890..7b448dcc171a 100644
--- a/drivers/gpu/drm/amd/display/dc/dcn31/dcn31_hwseq.c
+++ b/drivers/gpu/drm/amd/display/dc/dcn31/dcn31_hwseq.c
@@ -156,6 +156,9 @@  void dcn31_init_hw(struct dc *dc)
 		 */
 		struct dc_link *link = dc->links[i];
 
+		if (link->ep_type != DISPLAY_ENDPOINT_PHY)
+			continue;
+
 		link->link_enc->funcs->hw_init(link->link_enc);
 
 		/* Check for enabled DIG to identify enabled display */
@@ -220,7 +223,8 @@  void dcn31_init_hw(struct dc *dc)
 			for (i = 0; i < dc->link_count; i++) {
 				struct dc_link *link = dc->links[i];
 
-				if (link->link_enc->funcs->is_dig_enabled &&
+				if (link->ep_type == DISPLAY_ENDPOINT_PHY &&
+						link->link_enc->funcs->is_dig_enabled &&
 						link->link_enc->funcs->is_dig_enabled(link->link_enc) &&
 						dc->hwss.power_down) {
 					dc->hwss.power_down(dc);
diff --git a/drivers/gpu/drm/amd/display/dc/inc/link_enc_cfg.h b/drivers/gpu/drm/amd/display/dc/inc/link_enc_cfg.h
index 883dd8733ea4..2472c9aed095 100644
--- a/drivers/gpu/drm/amd/display/dc/inc/link_enc_cfg.h
+++ b/drivers/gpu/drm/amd/display/dc/inc/link_enc_cfg.h
@@ -88,4 +88,9 @@  struct link_encoder *link_enc_cfg_get_next_avail_link_enc(
 	const struct dc *dc,
 	const struct dc_state *state);
 
+/* Return DIG link encoder used by stream. NULL if unused. */
+struct link_encoder *link_enc_cfg_get_link_enc_used_by_stream(
+		struct dc_state *state,
+		const struct dc_stream_state *stream);
+
 #endif /* DC_INC_LINK_ENC_CFG_H_ */