drm/amd/display: Avoid pipe split when plane is too small

[Why]
The minimum plane size we can support in DML is 16x16. If we try to pass
a 16x16 plane with dynamic pipe split then validation will fail since it
tries to split it into two pipes, each 8x8.

Some userspace doesn't check that the commit fails and because the
commit fails the old state is retained, resulting in corruption.

[How]
Add a workaround to avoid pipe split if any plane is 16x16 or smaller.

Signed-off-by: Nicholas Kazlauskas <[e-mail]>
Reviewed-by: Aric Cyr <[e-mail]>
Acked-by: Rodrigo Siqueira <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/amd/display/dc/calcs/dcn_calcs.c

···
 		struct dc_debug_options *dbg,
 		struct dc_state *context)
 {
+	int i;
+
+	for (i = 0; i < MAX_PIPES; i++) {
+		struct pipe_ctx *pipe = &context->res_ctx.pipe_ctx[i];
+
+		/**
+		 * Workaround for avoiding pipe-split in cases where we'd split
+		 * planes that are too small, resulting in splits that aren't
+		 * valid for the scaler.
+		 */
+		if (pipe->plane_state &&
+		    (pipe->plane_state->dst_rect.width <= 16 ||
+		     pipe->plane_state->dst_rect.height <= 16 ||
+		     pipe->plane_state->src_rect.width <= 16 ||
+		     pipe->plane_state->src_rect.height <= 16)) {
+			hack_disable_optional_pipe_split(v);
+			return;
+		}
+	}
+
 	if (dbg->pipe_split_policy == MPC_SPLIT_AVOID)
 		hack_disable_optional_pipe_split(v);
 
···
 			dbg->force_single_disp_pipe_split)
 		hack_force_pipe_split(v, context->streams[0]->timing.pix_clk_100hz);
 }
-
 
 unsigned int get_highest_allowed_voltage_level(uint32_t hw_internal_rev, uint32_t pci_revision_id)
 {

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

···
 	} else if (dc->debug.force_single_disp_pipe_split)
 			force_split = true;
 
-	/* TODO: fix dc bugs and remove this split threshold thing */
 	for (i = 0; i < dc->res_pool->pipe_count; i++) {
 		struct pipe_ctx *pipe = &context->res_ctx.pipe_ctx[i];
 
+		/**
+		 * Workaround for avoiding pipe-split in cases where we'd split
+		 * planes that are too small, resulting in splits that aren't
+		 * valid for the scaler.
+		 */
+		if (pipe->plane_state &&
+		    (pipe->plane_state->dst_rect.width <= 16 ||
+		     pipe->plane_state->dst_rect.height <= 16 ||
+		     pipe->plane_state->src_rect.width <= 16 ||
+		     pipe->plane_state->src_rect.height <= 16))
+			avoid_split = true;
+
+		/* TODO: fix dc bugs and remove this split threshold thing */
 		if (pipe->stream && !pipe->prev_odm_pipe &&
 				(!pipe->top_pipe || pipe->top_pipe->plane_state != pipe->plane_state))
 			++plane_count;