drm/amd/display: Adjust downscaling limits for dcn314

[Why]
Lower max_downscale_ratio and ARGB888 downscale factor
to prevent cases where underflow may occur on dcn314

[How]
Set max_downscale_ratio to 400 and ARGB downscale factor
to 250 for dcn314

Reviewed-by: Nicholas Kazlauskas <[email protected]>
Acked-by: Alex Hung <[email protected]>
Signed-off-by: Daniel Miess <[email protected]>
Tested-by: Daniel Wheeler <[email protected]>
Signed-off-by: Alex Deucher <[email protected]>

Author: Daniel Miess

drivers/gpu/drm/amd/display/dc/dcn314/dcn314_resource.c

@@ -874,8 +874,9 @@ static const struct dc_plane_cap plane_cap = {
 	},
 
 	// 6:1 downscaling ratio: 1000/6 = 166.666
+	// 4:1 downscaling ratio for ARGB888 to prevent underflow during P010 playback: 1000/4 = 250
 	.max_downscale_factor = {
-			.argb8888 = 167,
+			.argb8888 = 250,
 			.nv12 = 167,
 			.fp16 = 167
 	},
@@ -1763,7 +1764,7 @@ static bool dcn314_resource_construct(
 	pool->base.underlay_pipe_index = NO_UNDERLAY_PIPE;
 	pool->base.pipe_count = pool->base.res_cap->num_timing_generator;
 	pool->base.mpcc_count = pool->base.res_cap->num_timing_generator;
-	dc->caps.max_downscale_ratio = 600;
+	dc->caps.max_downscale_ratio = 400;
 	dc->caps.i2c_speed_in_khz = 100;
 	dc->caps.i2c_speed_in_khz_hdcp = 100;
 	dc->caps.max_cursor_size = 256;