[PATCH 22/26] drm/i915/dp: Set relevant Downspread Ctrl DPCD bits for PR + Auxless ALPM

Ankit Nautiyal
2026-04-08T08:58:36Z

If a Panel Replay capable sink, supports Async Video timing in
PR active state, then source does not necessarily need to send AS SDPs
during PR active.

However, if asynchronous video timing is not supported, then for PR with
Aux-less ALPM, the source must transmit Adaptive-Sync SDPs for video
timing synchronization while PR is active.

If the source needs to send AS SDP during PR active, this requires setting
DPCD 0x0107[6] (FIXED_VTOTAL_AS_SDP_EN_IN_PR_ACTIVE). This applies whether
VRR is enabled (AVT/FAVT) or fixed-timing mode is used.

This bit defines AS SDP timing behavior during PR Active, even if AS SDPs
are briefly suspended.

Program the relevant Downspread Ctrl DPCD bits accordingly.

v2: Instead of Panel Replay check simply use AS SDP enable check. (Ville)
v3: Since the bit is defined in context of Panel Replay and AS SDP, add
a check for both. (Ville)

Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
---
.../gpu/drm/i915/display/intel_dp_link_training.c | 15 +++++++++++++--
.../gpu/drm/i915/display/intel_dp_link_training.h | 3 ++-
drivers/gpu/drm/i915/display/intel_dp_mst.c | 2 +-
3 files changed, 16 insertions(+), 4 deletions(-)

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 a26094223f78..d0b033d2cfb4 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
@@ -34,8 +34,10 @@
#include "intel_dp.h"
#include "intel_dp_link_training.h"
#include "intel_encoder.h"
+#include "intel_hdmi.h"
#include "intel_hotplug.h"
#include "intel_panel.h"
+#include "intel_psr.h"

#define LT_MSG_PREFIX "[CONNECTOR:%d:%s][ENCODER:%d:%s][%s] "
#define LT_MSG_ARGS(_intel_dp, _dp_phy) (_intel_dp)->attached_connector->base.base.id, \
@@ -710,11 +712,14 @@ static bool intel_dp_link_max_vswing_reached(struct intel_dp *intel_dp,
return true;
}

-void intel_dp_link_training_set_mode(struct intel_dp *intel_dp, int link_rate, bool is_vrr)
+void intel_dp_link_training_set_mode(struct intel_dp *intel_dp, int link_rate,
+ bool is_vrr,
+ bool pr_with_as_sdp_enable)
{
u8 link_config[2];

link_config[0] = is_vrr ? DP_MSA_TIMING_PAR_IGNORE_EN : 0;
+ link_config[0] |= pr_with_as_sdp_enable ? DP_FIXED_VTOTAL_AS_SDP_EN_IN_PR_ACTIVE : 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);
@@ -723,6 +728,10 @@ void intel_dp_link_training_set_mode(struct intel_dp *intel_dp, int link_rate, b
static void intel_dp_update_downspread_ctrl(struct intel_dp *intel_dp,
const struct intel_crtc_state *crtc_state)
{
+ bool pr_with_as_sdp_enable =
+ intel_psr_needs_alpm_aux_less(intel_dp, crtc_state) &&
+ crtc_state->infoframes.enable & intel_hdmi_infoframe_enable(DP_SDP_ADAPTIVE_SYNC);
+
/*
* Currently, we set the MSA ignore bit based on vrr.in_range.
* We can't really read that out during driver load since we don't have
@@ -737,7 +746,9 @@ static void intel_dp_update_downspread_ctrl(struct intel_dp *intel_dp,
* especially on the first real commit when clearing the inherited flag.
*/
intel_dp_link_training_set_mode(intel_dp,
- crtc_state->port_clock, crtc_state->vrr.in_range);
+ crtc_state->port_clock,
+ crtc_state->vrr.in_range,
+ pr_with_as_sdp_enable);
}

void intel_dp_link_training_set_bw(struct intel_dp *intel_dp,
diff --git a/drivers/gpu/drm/i915/display/intel_dp_link_training.h b/drivers/gpu/drm/i915/display/intel_dp_link_training.h
index 33dcbde6a408..18c34c1a472f 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_link_training.h
+++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.h
@@ -18,7 +18,8 @@ int intel_dp_init_lttpr_and_dprx_caps(struct intel_dp *intel_dp);
bool intel_dp_lttpr_transparent_mode_enabled(struct intel_dp *intel_dp);

void intel_dp_link_training_set_mode(struct intel_dp *intel_dp,
- int link_rate, bool is_vrr);
+ int link_rate, bool is_vrr,
+ bool pr_with_as_sdp_enable);
void intel_dp_link_training_set_bw(struct intel_dp *intel_dp,
int link_bw, int rate_select, int lane_count,
bool enhanced_framing, bool post_lt_adj_req);
diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
index e8de17834dcd..ffd1cf0aad9a 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
@@ -2142,7 +2142,7 @@ void intel_dp_mst_prepare_probe(struct intel_dp *intel_dp)

intel_dp_compute_rate(intel_dp, link_rate, &link_bw, &rate_select);

- intel_dp_link_training_set_mode(intel_dp, link_rate, false);
+ intel_dp_link_training_set_mode(intel_dp, link_rate, false, false);
intel_dp_link_training_set_bw(intel_dp, link_bw, rate_select, lane_count,
drm_dp_enhanced_frame_cap(intel_dp->dpcd), false);

--
2.45.2