-----Original Message-----
From: Nautiyal, Ankit K <ankit.k.nauti...@intel.com>
Sent: 07 August 2025 16:46
To: intel-gfx@lists.freedesktop.org; intel...@lists.freedesktop.org
Cc: ville.syrj...@linux.intel.com; jani.nik...@linux.intel.com; Golani,
Mitulkumar Ajitkumar <mitulkumar.ajitkumar.gol...@intel.com>; Nautiyal, Ankit
K <ankit.k.nauti...@intel.com>
Subject: [PATCH 08/12] drm/i915/display: Add guardband check for feature
latencies
Add a check during atomic crtc check phase to ensure the programmed VRR
guardband is sufficient to cover latencies introduced by enabled features such
as
DSC, PSR/PR, scalers, and DP SDPs.
Currently, the guardband is programmed to match the vblank length, so existing
checks in skl_is_vblank_too_short() are valid. However, upcoming changes will
optimize the guardband independently of vblank, making those checks incorrect.
Introduce an explicit guardband check to prepare for future updates that will
remove checking against the vblank length and later program an optimized
guardband.
v2: Use new helper for PSR2/Panel Replay latency.
Signed-off-by: Ankit Nautiyal <ankit.k.nauti...@intel.com>
---
drivers/gpu/drm/i915/display/intel_display.c | 138 +++++++++++++++++++
drivers/gpu/drm/i915/display/skl_watermark.c | 2 +-
drivers/gpu/drm/i915/display/skl_watermark.h | 1 +
3 files changed, 140 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/i915/display/intel_display.c
b/drivers/gpu/drm/i915/display/intel_display.c
index af4d54672d0d..c542a3110051 100644
--- a/drivers/gpu/drm/i915/display/intel_display.c
+++ b/drivers/gpu/drm/i915/display/intel_display.c
@@ -4227,6 +4227,138 @@ static int hsw_compute_linetime_wm(struct
intel_atomic_state *state,
return 0;
}
+static int
+cdclk_prefill_adjustment(const struct intel_crtc_state *crtc_state) {
+ struct intel_display *display = to_intel_display(crtc_state);
+ struct intel_atomic_state *state =
+ to_intel_atomic_state(crtc_state->uapi.state);
+ const struct intel_cdclk_state *cdclk_state;
+
+ cdclk_state = intel_atomic_get_cdclk_state(state);
+ if (IS_ERR(cdclk_state)) {
+ drm_WARN_ON(display->drm, PTR_ERR(cdclk_state));
+ return 1;
+ }
+
+ return min(1, DIV_ROUND_UP(crtc_state->pixel_rate,
+ 2 * intel_cdclk_logical(cdclk_state)));
+}
+
+static int
+dsc_prefill_latency(const struct intel_crtc_state *crtc_state, int
+linetime) {
+ const struct intel_crtc_scaler_state *scaler_state = &crtc_state-
scaler_state;
+ int chroma_downscaling_factor =
skl_scaler_chroma_downscale_factor(crtc_state);
+ struct intel_crtc *crtc = to_intel_crtc(crtc_state->uapi.crtc);
+ int num_scaler_users = hweight32(scaler_state->scaler_users);
+ u64 hscale_k[ARRAY_SIZE(scaler_state->scalers)];
+ u64 vscale_k[ARRAY_SIZE(scaler_state->scalers)];
+ u32 dsc_prefill_latency = 0;
+
+ if (!crtc_state->dsc.compression_enable ||
+ !num_scaler_users ||
+ num_scaler_users > crtc->num_scalers ||
+ num_scaler_users > ARRAY_SIZE(scaler_state->scalers))
+ return dsc_prefill_latency;
+
+ for (int i = 0; i < num_scaler_users; i++) {
+ hscale_k[i] = max(1000, mul_u32_u32(scaler_state-
scalers[i].hscale, 1000) >> 16);
+ vscale_k[i] = max(1000, mul_u32_u32(scaler_state-
scalers[i].vscale, 1000) >> 16);
+ }
+
+ dsc_prefill_latency =
+ intel_display_dsc_prefill_latency(num_scaler_users, hscale_k,
vscale_k,
+ chroma_downscaling_factor,
+
cdclk_prefill_adjustment(crtc_state),
+ linetime);
+
+ return dsc_prefill_latency;
+}
+
+static int
+scaler_prefill_latency(const struct intel_crtc_state *crtc_state, int
+linetime) {
+ const struct intel_crtc_scaler_state *scaler_state = &crtc_state-
scaler_state;
+ int chroma_downscaling_factor =
skl_scaler_chroma_downscale_factor(crtc_state);
+ int num_scaler_users = hweight32(scaler_state->scaler_users);
+ u64 hscale_k = 1000, vscale_k = 1000;
+ int scaler_prefill_latency = 0;
+
+ if (!num_scaler_users)
+ return scaler_prefill_latency;
+
+ if (num_scaler_users > 1) {
+ hscale_k = max(1000, mul_u32_u32(scaler_state-
scalers[0].hscale, 1000) >> 16);
+ vscale_k = max(1000, mul_u32_u32(scaler_state-
scalers[0].vscale, 1000) >> 16);
+ }
+
+ scaler_prefill_latency =
+ intel_display_scaler_prefill_latency(num_scaler_users, hscale_k,
vscale_k,
+ chroma_downscaling_factor,
+
cdclk_prefill_adjustment(crtc_state),
+ linetime);
+
+ return scaler_prefill_latency;
+}
+
+static int intel_crtc_check_guardband(struct intel_crtc_state
+*crtc_state) {
+ struct intel_display *display = to_intel_display(crtc_state);
+ const struct drm_display_mode *adjusted_mode = &crtc_state-
hw.adjusted_mode;
+ int dsc_prefill_time = 0;
+ int scaler_prefill_time;
+ int wm0_prefill_time;
+ int pkgc_max_latency;
+ int psr2_pr_latency;
+ int min_guardband;
+ int guardband_us;
+ int sagv_latency;
+ int linetime_us;
+ int sdp_latency;
+ int pm_delay;
+
+ if (!crtc_state->vrr.enable && !intel_vrr_always_use_vrr_tg(display))
+ return 0;
+
+ if (!adjusted_mode->crtc_clock)
+ return 0;
+
+ linetime_us = DIV_ROUND_UP(adjusted_mode->crtc_htotal * 1000,
+ adjusted_mode->crtc_clock);
+
+ pkgc_max_latency = skl_watermark_max_latency(display, 1);
+ sagv_latency = display->sagv.block_time_us;
+
+ wm0_prefill_time = skl_max_wm0_lines(crtc_state) * linetime_us + 20;
