[v3 4/4] drm/i915/display: Gate periodic AS SDP skip frames behind a module parameter

[Uma Shankar <uma.shankar@intel.com>]

Periodic AS SDP (skip frames) drives a Panel Replay panel down toward its
minimum refresh rate. It is a new, panel- and platform-sensitive behaviour,
so keep it opt-in rather than enabling it unconditionally.

Add a display module parameter, periodic_assdp_enable, shared by both the
i915 and xe drivers via the intel_display_params infrastructure. It defaults
to false (feature disabled); set it to true to enable periodic AS SDP.

Gate the feature at its single choke point, intel_pr_as_sdp_skip_frames():
returning a zero skip count when the parameter is off makes both the
PR_ALPM_CTL programming (intel_alpm_configure_pr_as_sdp()) and the DC3co
force-disable predicate (intel_alpm_pr_as_sdp_skip_frames_enabled()) a no-op,
so AS SDP continues to be sent on every frame as before.

Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Uma Shankar <uma.shankar@intel.com>
---
 drivers/gpu/drm/i915/display/intel_alpm.c           | 5 +++++
 drivers/gpu/drm/i915/display/intel_display_params.c | 6 ++++++
 drivers/gpu/drm/i915/display/intel_display_params.h | 1 +
 3 files changed, 12 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_alpm.c b/drivers/gpu/drm/i915/display/intel_alpm.c
index 03d5bf5c526f..e723fa56e4d4 100644
--- a/drivers/gpu/drm/i915/display/intel_alpm.c
+++ b/drivers/gpu/drm/i915/display/intel_alpm.c
@@ -392,11 +392,16 @@ static u32 get_pr_alpm_as_sdp_transmission_time(const struct intel_crtc_state *c
  */
 static u32 intel_pr_as_sdp_skip_frames(struct intel_dp *intel_dp)
 {
+	struct intel_display *display = to_intel_display(intel_dp);
 	const struct drm_display_info *info =
 		&intel_dp->attached_connector->base.display_info;
 	int max_vrefresh = info->monitor_range.max_vfreq;
 	int min_vrefresh = info->monitor_range.min_vfreq;
 
+	/* Off by default; gated by the periodic_assdp_enable module parameter. */
+	if (!display->params.periodic_assdp_enable)
+		return 0;
+
 	if (min_vrefresh <= 0 || max_vrefresh <= min_vrefresh)
 		return 0;
 
diff --git a/drivers/gpu/drm/i915/display/intel_display_params.c b/drivers/gpu/drm/i915/display/intel_display_params.c
index 2aed110c5b09..a845d29610cf 100644
--- a/drivers/gpu/drm/i915/display/intel_display_params.c
+++ b/drivers/gpu/drm/i915/display/intel_display_params.c
@@ -139,6 +139,12 @@ intel_display_param_named_unsafe(enable_dmc_wl, int, 0400,
 	"(-1=use per-chip default, 0=disabled, 1=enabled, 2=match any register, 3=always locked) "
 	"Default: -1");
 
+intel_display_param_named_unsafe(periodic_assdp_enable, bool, 0600,
+	"Enable periodic Adaptive-Sync SDP (AS SDP skip frames) for Panel Replay "
+	"to drive the panel down to its minimum refresh rate "
+	"(0=disabled, 1=enabled) "
+	"Default: 0");
+
 __maybe_unused
 static void _param_print_bool(struct drm_printer *p, const char *driver_name,
 			      const char *name, bool val)
diff --git a/drivers/gpu/drm/i915/display/intel_display_params.h b/drivers/gpu/drm/i915/display/intel_display_params.h
index b95ecf728daa..4d912aab4811 100644
--- a/drivers/gpu/drm/i915/display/intel_display_params.h
+++ b/drivers/gpu/drm/i915/display/intel_display_params.h
@@ -50,6 +50,7 @@ struct drm_printer;
 	param(bool, psr_safest_params, false, 0400) \
 	param(bool, enable_psr2_sel_fetch, true, 0400) \
 	param(int, enable_dmc_wl, -1, 0400) \
+	param(bool, periodic_assdp_enable, false, 0600) \
 
 #define MEMBER(T, member, ...) T member;
 struct intel_display_params {
-- 
2.50.1