[PATCH 04/12] drm/i915/display: Extract helpers to set dsc/scaler prefill latencies
Golani, Mitulkumar Ajitkumar
mitulkumar.ajitkumar.golani at intel.com
Mon Aug 18 10:37:13 UTC 2025
> -----Original Message-----
> From: Intel-gfx <intel-gfx-bounces at lists.freedesktop.org> On Behalf Of Ankit
> Nautiyal
> Sent: 18 August 2025 13:01
> To: intel-gfx at lists.freedesktop.org; intel-xe at lists.freedesktop.org
> Cc: ville.syrjala at linux.intel.com; Nautiyal, Ankit K <ankit.k.nautiyal at intel.com>
> Subject: [PATCH 04/12] drm/i915/display: Extract helpers to set dsc/scaler prefill
> latencies
>
> Currently dsc/scaler prefill latencies are handled during watermark calculations.
> With the optimized guardband, we need to compute the latencies to find the
> minimum guardband that works for most cases.
> Extract the helpers to compute these latencies, so that they can be used while
> computing vrr guardband.
>
> While at it, put declarations in reverse xmas tree order for better redability.
>
> v2: Initialize {h,v}scale_k to 0, and simplify the check in
> intel_display_scaler_prefill_latency(). (Mitul)
>
> Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal at intel.com>
> ---
> drivers/gpu/drm/i915/display/intel_display.c | 33 ++++++++++++++
> drivers/gpu/drm/i915/display/intel_display.h | 8 ++++
> drivers/gpu/drm/i915/display/skl_watermark.c | 46 +++++++++-----------
> 3 files changed, 62 insertions(+), 25 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_display.c
> b/drivers/gpu/drm/i915/display/intel_display.c
> index c1a3a95c65f0..62ec95a75154 100644
> --- a/drivers/gpu/drm/i915/display/intel_display.c
> +++ b/drivers/gpu/drm/i915/display/intel_display.c
> @@ -8328,3 +8328,36 @@ bool intel_scanout_needs_vtd_wa(struct
> intel_display *display)
>
> return IS_DISPLAY_VER(display, 6, 11) && i915_vtd_active(i915); }
> +
> +int intel_display_scaler_prefill_latency(int num_scaler_users, u64 hscale, u64
> vscale,
> + int chroma_downscaling_factor,
> + int cdclk_prefill_adjustment,
> + int linetime)
> +{
> + int scaler_prefill_latency;
> +
> + scaler_prefill_latency = 4 * linetime +
> + DIV_ROUND_UP_ULL((4 * linetime * hscale *
> vscale *
> + chroma_downscaling_factor),
> 1000000);
> +
> + scaler_prefill_latency *= cdclk_prefill_adjustment;
> +
> + return scaler_prefill_latency;
> +}
> +
> +int intel_display_dsc_prefill_latency(int num_scaler_users, u64 *hscale, u64
> *vscale,
> + int chroma_downscaling_factor,
> + int cdclk_prefill_adjustment,
> + int linetime)
> +{
> + int dsc_prefill_latency;
> +
> + dsc_prefill_latency = DIV_ROUND_UP(15 * linetime *
> +chroma_downscaling_factor, 10);
> +
> + for (int i = 0; i < num_scaler_users; i++)
> + dsc_prefill_latency = DIV_ROUND_UP_ULL(dsc_prefill_latency *
> hscale[i] * vscale[i],
> + 1000000);
> + dsc_prefill_latency *= cdclk_prefill_adjustment;
> +
> + return dsc_prefill_latency;
> +}
> diff --git a/drivers/gpu/drm/i915/display/intel_display.h
> b/drivers/gpu/drm/i915/display/intel_display.h
> index 37e2ab301a80..8d094b0a8c6b 100644
> --- a/drivers/gpu/drm/i915/display/intel_display.h
> +++ b/drivers/gpu/drm/i915/display/intel_display.h
> @@ -559,5 +559,13 @@ bool assert_port_valid(struct intel_display *display,
> enum port port);
>
> bool intel_scanout_needs_vtd_wa(struct intel_display *display); int
> intel_crtc_num_joined_pipes(const struct intel_crtc_state *crtc_state);
> +int intel_display_scaler_prefill_latency(int num_scaler_users, u64 hscale, u64
> vscale,
> + int chroma_downscaling_factor,
> + int cdclk_prefill_adjustment,
> + int linetime);
> +int intel_display_dsc_prefill_latency(int num_scaler_users, u64 *hscale, u64
> *vscale,
> + int chroma_downscaling_factor,
> + int cdclk_prefill_adjustment,
> + int linetime);
>
> #endif
> diff --git a/drivers/gpu/drm/i915/display/skl_watermark.c
> b/drivers/gpu/drm/i915/display/skl_watermark.c
> index 97b42bbf5642..f0213785e9fc 100644
> --- a/drivers/gpu/drm/i915/display/skl_watermark.c
> +++ b/drivers/gpu/drm/i915/display/skl_watermark.c
> @@ -2179,11 +2179,12 @@ cdclk_prefill_adjustment(const struct
> intel_crtc_state *crtc_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);
> - const struct intel_crtc_scaler_state *scaler_state =
> - &crtc_state->scaler_state;
> int num_scaler_users = hweight32(scaler_state->scaler_users);
> - int chroma_downscaling_factor =
> skl_scaler_chroma_downscale_factor(crtc_state);
> + 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 || @@ -2191,18 +2192,16
> @@ dsc_prefill_latency(const struct intel_crtc_state *crtc_state, int linetime)
> num_scaler_users > crtc->num_scalers)
> return dsc_prefill_latency;
>
> - dsc_prefill_latency = DIV_ROUND_UP(15 * linetime *
> chroma_downscaling_factor, 10);
> -
> for (int i = 0; i < num_scaler_users; i++) {
> - u64 hscale_k, vscale_k;
> -
> - hscale_k = max(1000, mul_u32_u32(scaler_state-
> >scalers[i].hscale, 1000) >> 16);
> - vscale_k = max(1000, mul_u32_u32(scaler_state-
> >scalers[i].vscale, 1000) >> 16);
> - dsc_prefill_latency = DIV_ROUND_UP_ULL(dsc_prefill_latency *
> hscale_k * vscale_k,
> - 1000000);
> + 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 *= cdclk_prefill_adjustment(crtc_state);
> + 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;
> }
> @@ -2210,28 +2209,25 @@ dsc_prefill_latency(const struct intel_crtc_state
> *crtc_state, int linetime) 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;
> + 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 = 0, vscale_k = 0;
> int scaler_prefill_latency = 0;
>
> if (!num_scaler_users)
> return scaler_prefill_latency;
>
> - scaler_prefill_latency = 4 * linetime;
> -
> if (num_scaler_users > 1) {
> - u64 hscale_k = max(1000, mul_u32_u32(scaler_state-
> >scalers[0].hscale, 1000) >> 16);
> - u64 vscale_k = max(1000, mul_u32_u32(scaler_state-
> >scalers[0].vscale, 1000) >> 16);
> - int chroma_downscaling_factor =
> skl_scaler_chroma_downscale_factor(crtc_state);
> - int latency;
> -
> - latency = DIV_ROUND_UP_ULL((4 * linetime * hscale_k *
> vscale_k *
> - chroma_downscaling_factor),
> 1000000);
> - scaler_prefill_latency += latency;
> + 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 *= cdclk_prefill_adjustment(crtc_state);
> + scaler_prefill_latency =
> + intel_display_scaler_prefill_latency(num_scaler_users, hscale_k,
> vscale_k,
> + chroma_downscaling_factor,
> +
> cdclk_prefill_adjustment(crtc_state),
> + linetime);
Reviewed-by: Mitul Golani <mitulkumar.ajitkumar.golani at intel.com>
>
> return scaler_prefill_latency;
> }
> --
> 2.45.2
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