[PATCH 12/16] drm/amd/display: Require minimum VBlank size for stutter optimization

[Hamza Mahfooz]

From: Dillon Varone <dillon.varone at amd.com>

If the nominal VBlank is too small, optimizing for stutter can cause
the prefetch bandwidth to increase drasticaly, resulting in higher
clock and power requirements. Only optimize if it is >3x the stutter
latency.

Cc: stable at vger.kernel.org
Reviewed-by: Austin Zheng <austin.zheng at amd.com>
Signed-off-by: Dillon Varone <dillon.varone at amd.com>
Signed-off-by: Hamza Mahfooz <hamza.mahfooz at amd.com>
---
 .../dc/dml2/dml21/src/dml2_pmo/dml2_pmo_dcn4_fams2.c  | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/dc/dml2/dml21/src/dml2_pmo/dml2_pmo_dcn4_fams2.c b/drivers/gpu/drm/amd/display/dc/dml2/dml21/src/dml2_pmo/dml2_pmo_dcn4_fams2.c
index 5a09dd298e6f..92269f0e50ed 100644
--- a/drivers/gpu/drm/amd/display/dc/dml2/dml21/src/dml2_pmo/dml2_pmo_dcn4_fams2.c
+++ b/drivers/gpu/drm/amd/display/dc/dml2/dml21/src/dml2_pmo/dml2_pmo_dcn4_fams2.c
@@ -8,6 +8,7 @@
 #include "dml2_pmo_dcn4_fams2.h"
 
 static const double MIN_VACTIVE_MARGIN_PCT = 0.25; // We need more than non-zero margin because DET buffer granularity can alter vactive latency hiding
+static const double MIN_BLANK_STUTTER_FACTOR = 3.0;
 
 static const struct dml2_pmo_pstate_strategy base_strategy_list_1_display[] = {
 	// VActive Preferred
@@ -2140,6 +2141,7 @@ bool pmo_dcn4_fams2_init_for_stutter(struct dml2_pmo_init_for_stutter_in_out *in
 	struct dml2_pmo_instance *pmo = in_out->instance;
 	bool stutter_period_meets_z8_eco = true;
 	bool z8_stutter_optimization_too_expensive = false;
+	bool stutter_optimization_too_expensive = false;
 	double line_time_us, vblank_nom_time_us;
 
 	unsigned int i;
@@ -2161,10 +2163,15 @@ bool pmo_dcn4_fams2_init_for_stutter(struct dml2_pmo_init_for_stutter_in_out *in
 		line_time_us = (double)in_out->base_display_config->display_config.stream_descriptors[i].timing.h_total / (in_out->base_display_config->display_config.stream_descriptors[i].timing.pixel_clock_khz * 1000) * 1000000;
 		vblank_nom_time_us = line_time_us * in_out->base_display_config->display_config.stream_descriptors[i].timing.vblank_nom;
 
-		if (vblank_nom_time_us < pmo->soc_bb->power_management_parameters.z8_stutter_exit_latency_us) {
+		if (vblank_nom_time_us < pmo->soc_bb->power_management_parameters.z8_stutter_exit_latency_us * MIN_BLANK_STUTTER_FACTOR) {
 			z8_stutter_optimization_too_expensive = true;
 			break;
 		}
+
+		if (vblank_nom_time_us < pmo->soc_bb->power_management_parameters.stutter_enter_plus_exit_latency_us * MIN_BLANK_STUTTER_FACTOR) {
+			stutter_optimization_too_expensive = true;
+			break;
+		}
 	}
 
 	pmo->scratch.pmo_dcn4.num_stutter_candidates = 0;
@@ -2180,7 +2187,7 @@ bool pmo_dcn4_fams2_init_for_stutter(struct dml2_pmo_init_for_stutter_in_out *in
 		pmo->scratch.pmo_dcn4.z8_vblank_optimizable = false;
 	}
 
-	if (pmo->soc_bb->power_management_parameters.stutter_enter_plus_exit_latency_us > 0) {
+	if (!stutter_optimization_too_expensive && pmo->soc_bb->power_management_parameters.stutter_enter_plus_exit_latency_us > 0) {
 		pmo->scratch.pmo_dcn4.optimal_vblank_reserved_time_for_stutter_us[pmo->scratch.pmo_dcn4.num_stutter_candidates] = (unsigned int)pmo->soc_bb->power_management_parameters.stutter_enter_plus_exit_latency_us;
 		pmo->scratch.pmo_dcn4.num_stutter_candidates++;
 	}
-- 
2.46.1