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* [PATCH] drm/i915/display: Set SPREAD_AMP bit to enable SSC
@ 2025-09-18 21:28 Khaled Almahallawy
  2025-09-18 22:45 ` ✓ CI.KUnit: success for " Patchwork
                   ` (2 more replies)
  0 siblings, 3 replies; 5+ messages in thread
From: Khaled Almahallawy @ 2025-09-18 21:28 UTC (permalink / raw)
  To: intel-gfx, intel-xe; +Cc: Khaled Almahallawy, Uma Shankar, Jani Nikula

According to DP Specs[1]:
"SSC is enabled or disabled when the SPREAD_AMP bit in the
DOWNSPREAD_CTRL register is set or cleared (DPCD 00107h[4]  = 1 or 0,
respectively)."

Set the SPREAD_AMP bit before starting link training to ensure SSC
is enabled as required.

[1]: DisplayPort Standard v2.1 - Sec 2.2.3.1 De-spreading of the
Regenerated Stream Clock

Cc: Uma Shankar <uma.shankar@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Khaled Almahallawy <khaled.almahallawy@intel.com>
---
 drivers/gpu/drm/i915/display/intel_dp_link_training.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dp_link_training.c b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
index 27f3716bdc1f..db2ea3c51a5f 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
@@ -711,9 +711,13 @@ static bool intel_dp_link_max_vswing_reached(struct intel_dp *intel_dp,
 
 void intel_dp_link_training_set_mode(struct intel_dp *intel_dp, int link_rate, bool is_vrr)
 {
+	struct intel_display *display = to_intel_display(intel_dp);
 	u8 link_config[2];
+	bool ssc_enabled = intel_panel_use_ssc(display) &&
+			(intel_dp->dpcd[DP_MAX_DOWNSPREAD] & DP_MAX_DOWNSPREAD_0_5);
 
-	link_config[0] = is_vrr ? DP_MSA_TIMING_PAR_IGNORE_EN : 0;
+	link_config[0] = (is_vrr ? DP_MSA_TIMING_PAR_IGNORE_EN : 0) |
+		(ssc_enabled ? DP_SPREAD_AMP_0_5 : 0);
 	link_config[1] = drm_dp_is_uhbr_rate(link_rate) ?
 			 DP_SET_ANSI_128B132B : DP_SET_ANSI_8B10B;
 	drm_dp_dpcd_write(&intel_dp->aux, DP_DOWNSPREAD_CTRL, link_config, 2);
-- 
2.43.0


^ permalink raw reply related	[flat|nested] 5+ messages in thread
end of thread, other threads:[~2025-09-22 20:06 UTC | newest]

Thread overview: 5+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2025-09-18 21:28 [PATCH] drm/i915/display: Set SPREAD_AMP bit to enable SSC Khaled Almahallawy
2025-09-18 22:45 ` ✓ CI.KUnit: success for " Patchwork
2025-09-18 23:17 ` ✓ Xe.CI.BAT: " Patchwork
2025-09-19 10:26 ` [PATCH] " Jani Nikula
2025-09-22 20:06   ` Almahallawy, Khaled

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