drm/amd/display: Guard DST_Y_PREFETCH register overflow in DCN21

[why]
DST_Y_PREFETCH can overflow when DestinationLinesForPrefetch values are
too large due to the former being limited to 8 bits.

[how]
Set the maximum value of DestinationLinesForPrefetch to be 255 * refclk
period.

Reviewed-by: Laktyushkin Dmytro <dmytro.laktyushkin@amd.com>
Acked-by: Solomon Chiu <solomon.chiu@amd.com>
Signed-off-by: Victor Lu <victorchengchi.lu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

diff --git a/drivers/gpu/drm/amd/display/dc/dml/dcn21/display_mode_vba_21.c b/drivers/gpu/drm/amd/display/dc/dml/dcn21/display_mode_vba_21.c
index 506797c721ed9ac342bf281d0681e436bb8bae93..4136eb8256cb53509c06dcffbc1d67cc784881ff 100644 (file)
--- a/drivers/gpu/drm/amd/display/dc/dml/dcn21/display_mode_vba_21.c
+++ b/drivers/gpu/drm/amd/display/dc/dml/dcn21/display_mode_vba_21.c
@@ -841,6 +841,9 @@ static bool CalculatePrefetchSchedule(
        else
                *DestinationLinesForPrefetch = dst_y_prefetch_equ;
 
+       // Limit to prevent overflow in DST_Y_PREFETCH register
+       *DestinationLinesForPrefetch = dml_min(*DestinationLinesForPrefetch, 63.75);
+
        dml_print("DML: VStartup: %d\n", VStartup);
        dml_print("DML: TCalc: %f\n", TCalc);
        dml_print("DML: TWait: %f\n", TWait);