> -----Original Message-----
> From: Ville Syrjala <[email protected]>
> Sent: Wednesday, October 15, 2025 12:48 AM
> To: [email protected]
> Cc: [email protected]; Shankar, Uma <[email protected]>
> Subject: [PATCH v2 6/9] drm/i915/scaler: Add scaler prefill helpers
>
> From: Ville Syrjälä <[email protected]>
>
> Add helpers to compute the required prefill line count and adjustment factors
> for
> the scalers.
>
> The "1st" variants hand out numbers for the first scaler stage in the
> pipeline (pipe
> scaler if no plane scalers are enabled, or the max from all the plane
> scaler). The
> "2nd" variants deal with second scaler stage (pipe scaler when plane scaling
> is
> also enabled, otherwise there is no second stage).
>
> The _worst() variants give out worst case estimates, meant for guardband
> sizing.
> The other variants are meant for the actual vblank/guardband length check vs.
> prefill+pkgc/sagv latency.
>
> A few other helpers are added for the purpose of the WM0 prefill worst case
> estimates (to be introduced later).
>
> The returned numbers are in .16 binary fixed point.
>
> TODO: pretty rough, should check the actual scaler max scaling
> factors instead of just assuming 3x everywhere
>
> v2: Drop debugs
>
> Reviewed-by: Uma Shankar <[email protected]> #v1
> Signed-off-by: Ville Syrjälä <[email protected]>
> ---
> drivers/gpu/drm/i915/display/skl_scaler.c | 168 ++++++++++++++++++++++
> drivers/gpu/drm/i915/display/skl_scaler.h | 11 ++
> 2 files changed, 179 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/display/skl_scaler.c
> b/drivers/gpu/drm/i915/display/skl_scaler.c
> index c6cccf170ff1..47cdea75d27c 100644
> --- a/drivers/gpu/drm/i915/display/skl_scaler.c
> +++ b/drivers/gpu/drm/i915/display/skl_scaler.c
> @@ -968,3 +968,171 @@ void adl_scaler_ecc_unmask(const struct
> intel_crtc_state *crtc_state)
> 1);
> intel_de_write(display, XELPD_DISPLAY_ERR_FATAL_MASK, 0); }
> +
> +static unsigned int skl_scaler_scale(const struct intel_crtc_state
> +*crtc_state, int i) {
> + const struct intel_crtc_scaler_state *scaler_state =
> + &crtc_state->scaler_state;
> +
> + return DIV_ROUND_UP_ULL(mul_u32_u32(scaler_state-
> >scalers[i].hscale,
> + scaler_state->scalers[i].vscale),
> + 0x10000);
> +}
> +
> +static unsigned int skl_scaler_downscale(const struct intel_crtc_state
> +*crtc_state, int i) {
> + return max(0x10000, skl_scaler_scale(crtc_state, i)); }
> +
> +static unsigned int skl_plane_scaler_downscale(const struct
> +intel_crtc_state *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;
> + unsigned int scale = 0x10000;
> + int i;
> +
> + for (i = 0; i < crtc->num_scalers; i++) {
> + /* ignore pfit */
> + if (i == scaler_state->scaler_id)
> + continue;
> +
> + if (!scaler_state->scalers[i].in_use)
> + continue;
> +
> + scale = max(scale, skl_scaler_downscale(crtc_state, i));
> + }
> +
> + return scale;
> +}
> +
> +static unsigned int skl_pipe_scaler_downscale(const struct
> +intel_crtc_state *crtc_state) {
> + const struct intel_crtc_scaler_state *scaler_state =
> + &crtc_state->scaler_state;
> +
> + if (!crtc_state->pch_pfit.enabled)
> + return 0x10000;
Hi Ville,
It seems CI has some issue with bound check for scaler.
Maybe good to add a check here.
Regards,
Uma Shankar
> + return skl_scaler_downscale(crtc_state, scaler_state->scaler_id); }
> +
> +unsigned int skl_scaler_1st_prefill_adjustment(const struct
> +intel_crtc_state *crtc_state) {
> + const struct intel_crtc_scaler_state *scaler_state =
> + &crtc_state->scaler_state;
> + int num_scalers = hweight32(scaler_state->scaler_users);
> +
> + if (num_scalers < 1)
> + return 0x10000;
> +
> + if (num_scalers == 1 && crtc_state->pch_pfit.enabled)
> + return skl_pipe_scaler_downscale(crtc_state);
> + else
> + return skl_plane_scaler_downscale(crtc_state);
> +}
> +
> +unsigned int skl_scaler_2nd_prefill_adjustment(const struct
> +intel_crtc_state *crtc_state) {
> + const struct intel_crtc_scaler_state *scaler_state =
> + &crtc_state->scaler_state;
> + int num_scalers = hweight32(scaler_state->scaler_users);
> +
> + if (num_scalers < 2)
> + return 0x10000;
> +
> + return skl_pipe_scaler_downscale(crtc_state);
> +}
> +
> +unsigned int skl_scaler_1st_prefill_lines(const struct intel_crtc_state
> +*crtc_state) {
> + const struct intel_crtc_scaler_state *scaler_state =
> + &crtc_state->scaler_state;
> + int num_scalers = hweight32(scaler_state->scaler_users);
> +
> + if (num_scalers > 0)
> + return 4 << 16;
> +
> + return 0;
> +}
> +
> +unsigned int skl_scaler_2nd_prefill_lines(const struct intel_crtc_state
> +*crtc_state) {
> + const struct intel_crtc_scaler_state *scaler_state =
> + &crtc_state->scaler_state;
> + int num_scalers = hweight32(scaler_state->scaler_users);
> +
> + if (num_scalers > 1 && crtc_state->pch_pfit.enabled)
> + return 4 << 16;
> +
> + return 0;
> +}
> +
> +static unsigned int _skl_scaler_max_scale(const struct intel_crtc_state
> *crtc_state,
> + unsigned int max_scale)
> +{
> + struct intel_display *display = to_intel_display(crtc_state);
> +
> + /*
> + * Downscaling requires increasing cdclk, so max scale
> + * factor is limited to the max_dotclock/dotclock ratio.
> + *
> + * FIXME find out the max downscale factors properly
> + */
> + return min(max_scale, DIV_ROUND_UP_ULL((u64)display-
> >cdclk.max_dotclk_freq << 16,
> + crtc_state-
> >hw.pipe_mode.crtc_clock));
> +}
> +
> +static unsigned int skl_scaler_max_scale(const struct intel_crtc_state
> +*crtc_state) {
> + struct intel_crtc *crtc = to_intel_crtc(crtc_state->uapi.crtc);
> + unsigned int max_scale;
> +
> + if (crtc->num_scalers < 1)
> + return 0x10000;
> +
> + /* FIXME find out the max downscale factors properly */
> + max_scale = 9 << 16;
> +
> + return _skl_scaler_max_scale(crtc_state, max_scale); }
> +
> +unsigned int skl_scaler_1st_prefill_adjustment_worst(const struct
> +intel_crtc_state *crtc_state) {
> + struct intel_crtc *crtc = to_intel_crtc(crtc_state->uapi.crtc);
> +
> + if (crtc->num_scalers > 0)
> + return skl_scaler_max_scale(crtc_state);
> + else
> + return 0x10000;
> +}
> +
> +unsigned int skl_scaler_2nd_prefill_adjustment_worst(const struct
> +intel_crtc_state *crtc_state) {
> + struct intel_crtc *crtc = to_intel_crtc(crtc_state->uapi.crtc);
> +
> + if (crtc->num_scalers > 1)
> + return skl_scaler_max_scale(crtc_state);
> + else
> + return 0x10000;
> +}
> +
> +unsigned int skl_scaler_1st_prefill_lines_worst(const struct
> +intel_crtc_state *crtc_state) {
> + struct intel_crtc *crtc = to_intel_crtc(crtc_state->uapi.crtc);
> +
> + if (crtc->num_scalers > 0)
> + return 4 << 16;
> + else
> + return 0;
> +}
> +
> +unsigned int skl_scaler_2nd_prefill_lines_worst(const struct
> +intel_crtc_state *crtc_state) {
> + struct intel_crtc *crtc = to_intel_crtc(crtc_state->uapi.crtc);
> +
> + if (crtc->num_scalers > 1)
> + return 4 << 16;
> + else
> + return 0;
> +}
> diff --git a/drivers/gpu/drm/i915/display/skl_scaler.h
> b/drivers/gpu/drm/i915/display/skl_scaler.h
> index 12a19016c5f6..6fab40d2b4ee 100644
> --- a/drivers/gpu/drm/i915/display/skl_scaler.h
> +++ b/drivers/gpu/drm/i915/display/skl_scaler.h
> @@ -45,4 +45,15 @@ skl_scaler_mode_valid(struct intel_display *display, void
> adl_scaler_ecc_mask(const struct intel_crtc_state *crtc_state);
>
> void adl_scaler_ecc_unmask(const struct intel_crtc_state *crtc_state);
> +
> +unsigned int skl_scaler_1st_prefill_adjustment_worst(const struct
> +intel_crtc_state *crtc_state); unsigned int
> +skl_scaler_2nd_prefill_adjustment_worst(const struct intel_crtc_state
> +*crtc_state); unsigned int skl_scaler_1st_prefill_lines_worst(const
> +struct intel_crtc_state *crtc_state); unsigned int
> +skl_scaler_2nd_prefill_lines_worst(const struct intel_crtc_state
> +*crtc_state);
> +
> +unsigned int skl_scaler_1st_prefill_adjustment(const struct
> +intel_crtc_state *crtc_state); unsigned int
> +skl_scaler_2nd_prefill_adjustment(const struct intel_crtc_state
> +*crtc_state); unsigned int skl_scaler_1st_prefill_lines(const struct
> +intel_crtc_state *crtc_state); unsigned int
> +skl_scaler_2nd_prefill_lines(const struct intel_crtc_state
> +*crtc_state);
> +
> #endif
> --
> 2.49.1
