Re: [RFC v2 5/6] drm/i915/scaler: Check if vblank is sufficient for scaler

["Nautiyal, Ankit K" <ankit.k.nautiyal@intel.com>]

On 12/17/2024 11:37 PM, Mitul Golani wrote:
> Check if vblank is too short for scaler prefill latency.
>
> Signed-off-by: Mitul Golani <mitulkumar.ajitkumar.golani@intel.com>
> ---
>   drivers/gpu/drm/i915/display/skl_watermark.c | 22 ++++++++++++++++++++
>   1 file changed, 22 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/display/skl_watermark.c b/drivers/gpu/drm/i915/display/skl_watermark.c
> index d3506e8ccd9b..a538e2b82c12 100644
> --- a/drivers/gpu/drm/i915/display/skl_watermark.c
> +++ b/drivers/gpu/drm/i915/display/skl_watermark.c
> @@ -2292,6 +2292,27 @@ static int icl_build_plane_wm(struct intel_crtc_state *crtc_state,
>   	return 0;
>   }
>   
> +static int
> +scaler_prefill_time(const struct intel_crtc_state *crtc_state)
> +{
> +	const struct intel_crtc_scaler_state *scaler_state =
> +					&crtc_state->scaler_state;
> +	int scaler_users = scaler_state->scaler_users;
> +	int count = 0;
> +	int hscale = scaler_state->scalers[0].hscale;
> +	int vscale = scaler_state->scalers[0].vscale;
> +
> +	while (scaler_users) {
> +		count += scaler_users & 1;
> +		scaler_users >>= 1;
> +	}
> +
> +	if (count > 1)
> +		return (4 * crtc_state->linetime * hscale * vscale);

This will not work. We need to take proper precision into account to do 
this calculation.

currently hscale,vscale are left shifted by 16.

Regards,

Ankit

> +	else
> +		return (4 * crtc_state->linetime);
> +}
> +
>   static bool
>   skl_is_vblank_too_short(const struct intel_crtc_state *crtc_state,
>   			int wm0_lines, int latency)
> @@ -2302,6 +2323,7 @@ skl_is_vblank_too_short(const struct intel_crtc_state *crtc_state,
>   	/* FIXME missing scaler and DSC pre-fill time */
>   	return crtc_state->framestart_delay +
>   		intel_usecs_to_scanlines(adjusted_mode, latency) +
> +		scaler_prefill_time(crtc_state) +
>   		wm0_lines >
>   		adjusted_mode->crtc_vtotal - adjusted_mode->crtc_vblank_start;
>   }