drm/amd/display: Minimize DSC resource re-assignment

[why]
Assigning a different DSC resource than the one previosly used is
currently not handled. This causes black screen on mode change when more
than one monitor is connected on some ASICs.

[how]
- Acquire the previously used DSC if available
- Make sure re-program is triggered if new DSC is used

Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Nikola Cornij <nikola.cornij@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -2666,6 +2666,9 @@ bool pipe_need_reprogram(
 		false == pipe_ctx_old->stream->dpms_off)
 		return true;
 
+	if (pipe_ctx_old->stream_res.dsc != pipe_ctx->stream_res.dsc)
+		return true;
+
 	return false;
 }
 

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

@@ -1663,22 +1663,32 @@ enum dc_status dcn20_build_mapped_resource(const struct dc *dc, struct dc_state
 }
 
 
-static void acquire_dsc(struct resource_context *res_ctx,
-			const struct resource_pool *pool,
+static void acquire_dsc(const struct dc *dc,
+			struct resource_context *res_ctx,
 			struct display_stream_compressor **dsc,
 			int pipe_idx)
 {
 	int i;
+	const struct resource_pool *pool = dc->res_pool;
+	struct display_stream_compressor *dsc_old = dc->current_state->res_ctx.pipe_ctx[pipe_idx].stream_res.dsc;
 
-	ASSERT(*dsc == NULL);
+	ASSERT(*dsc == NULL); /* If this ASSERT fails, dsc was not released properly */
 	*dsc = NULL;
 
+	/* Always do 1-to-1 mapping when number of DSCs is same as number of pipes */
 	if (pool->res_cap->num_dsc == pool->res_cap->num_opp) {
 		*dsc = pool->dscs[pipe_idx];
 		res_ctx->is_dsc_acquired[pipe_idx] = true;
 		return;
 	}
 
+	/* Return old DSC to avoid the need for re-programming */
+	if (dsc_old && !res_ctx->is_dsc_acquired[dsc_old->inst]) {
+		*dsc = dsc_old;
+		res_ctx->is_dsc_acquired[dsc_old->inst] = true;
+		return ;
+	}
+
 	/* Find first free DSC */
 	for (i = 0; i < pool->res_cap->num_dsc; i++)
 		if (!res_ctx->is_dsc_acquired[i]) {
@@ -1710,7 +1720,6 @@ enum dc_status dcn20_add_dsc_to_stream_resource(struct dc *dc,
 {
 	enum dc_status result = DC_OK;
 	int i;
-	const struct resource_pool *pool = dc->res_pool;
 
 	/* Get a DSC if required and available */
 	for (i = 0; i < dc->res_pool->pipe_count; i++) {
@@ -1722,7 +1731,7 @@ enum dc_status dcn20_add_dsc_to_stream_resource(struct dc *dc,
 		if (pipe_ctx->stream_res.dsc)
 			continue;
 
-		acquire_dsc(&dc_ctx->res_ctx, pool, &pipe_ctx->stream_res.dsc, i);
+		acquire_dsc(dc, &dc_ctx->res_ctx, &pipe_ctx->stream_res.dsc, i);
 
 		/* The number of DSCs can be less than the number of pipes */
 		if (!pipe_ctx->stream_res.dsc) {
@@ -1850,12 +1859,13 @@ static void swizzle_to_dml_params(
 }
 
 bool dcn20_split_stream_for_odm(
+		const struct dc *dc,
 		struct resource_context *res_ctx,
-		const struct resource_pool *pool,
 		struct pipe_ctx *prev_odm_pipe,
 		struct pipe_ctx *next_odm_pipe)
 {
 	int pipe_idx = next_odm_pipe->pipe_idx;
+	const struct resource_pool *pool = dc->res_pool;
 
 	*next_odm_pipe = *prev_odm_pipe;
 
@@ -1913,7 +1923,7 @@ bool dcn20_split_stream_for_odm(
 	}
 	next_odm_pipe->stream_res.opp = pool->opps[next_odm_pipe->pipe_idx];
 	if (next_odm_pipe->stream->timing.flags.DSC == 1) {
-		acquire_dsc(res_ctx, pool, &next_odm_pipe->stream_res.dsc, next_odm_pipe->pipe_idx);
+		acquire_dsc(dc, res_ctx, &next_odm_pipe->stream_res.dsc, next_odm_pipe->pipe_idx);
 		ASSERT(next_odm_pipe->stream_res.dsc);
 		if (next_odm_pipe->stream_res.dsc == NULL)
 			return false;
@@ -2792,7 +2802,7 @@ bool dcn20_fast_validate_bw(
 			hsplit_pipe = dcn20_find_secondary_pipe(dc, &context->res_ctx, dc->res_pool, pipe);
 			ASSERT(hsplit_pipe);
 			if (!dcn20_split_stream_for_odm(
-					&context->res_ctx, dc->res_pool,
+					dc, &context->res_ctx,
 					pipe, hsplit_pipe))
 				goto validate_fail;
 			pipe_split_from[hsplit_pipe->pipe_idx] = pipe_idx;
@@ -2821,7 +2831,7 @@ bool dcn20_fast_validate_bw(
 				}
 				if (context->bw_ctx.dml.vba.ODMCombineEnabled[pipe_idx]) {
 					if (!dcn20_split_stream_for_odm(
-							&context->res_ctx, dc->res_pool,
+							dc, &context->res_ctx,
 							pipe, hsplit_pipe))
 						goto validate_fail;
 					dcn20_build_mapped_resource(dc, context, pipe->stream);

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

@@ -136,8 +136,8 @@ void dcn20_split_stream_for_mpc(
 		struct pipe_ctx *primary_pipe,
 		struct pipe_ctx *secondary_pipe);
 bool dcn20_split_stream_for_odm(
+		const struct dc *dc,
 		struct resource_context *res_ctx,
-		const struct resource_pool *pool,
 		struct pipe_ctx *prev_odm_pipe,
 		struct pipe_ctx *next_odm_pipe);
 struct pipe_ctx *dcn20_find_secondary_pipe(struct dc *dc,