Re: [PATCH v4 6/7] drm/i915/scaler: Check if vblank is sufficient for scaler

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

On 1/8/2025 6:05 PM, Mitul Golani wrote:
> Check if vblank is too short for scaler prefill latency.

Perhaps we can elaborate a bit.

Also add Bspec# in trailer.

>
> --v2:
> - Use hweight* family of functions for counting bits. [Jani]
> - Update precision handling for hscale and vscale. [Ankit]
> - Consider chroma downscaling factor during latency
> calculation. [Ankit]
> - Replace function name from scaler_prefill_time to
> scaler_prefill_latency.
>
> --v3:
> - hscale_k and vscale_k values are already left shifted by 16,
> after multiplying by 1000, those need to be right shifted to 16. [Ankit]
> - Replace YCBCR444 to YCBCR420. [Ankit]
> - Divide by 1000 * 1000 in end to get correct precision. [Ankit]
> - Initialise latency to 0 to avoid any garbage.
>
> Signed-off-by: Mitul Golani <mitulkumar.ajitkumar.golani@intel.com>
> ---
>   drivers/gpu/drm/i915/display/skl_watermark.c | 31 ++++++++++++++++++++
>   1 file changed, 31 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/display/skl_watermark.c b/drivers/gpu/drm/i915/display/skl_watermark.c
> index f4458d1185b3..fe91854e456c 100644
> --- a/drivers/gpu/drm/i915/display/skl_watermark.c
> +++ b/drivers/gpu/drm/i915/display/skl_watermark.c
> @@ -2292,6 +2292,36 @@ static int icl_build_plane_wm(struct intel_crtc_state *crtc_state,
>   	return 0;
>   }
>   
> +static int
> +scaler_prefill_latency(const struct intel_crtc_state *crtc_state)
> +{
> +	const struct intel_crtc_scaler_state *scaler_state =
> +					&crtc_state->scaler_state;
> +	int count = hweight32(scaler_state->scaler_users);
> +	int latency = 0;
> +	long long  hscale_k =
> +		mul_u32_u32(scaler_state->scalers[0].hscale, 1000) >> 16;
> +	long long vscale_k =
> +		mul_u32_u32(scaler_state->scalers[0].vscale, 1000) >> 16;
> +
> +	if (!count)
> +		return latency;
> +
> +	if (count > 1) {
> +		int chroma_downscaling_factor =
> +			crtc_state->output_format == INTEL_OUTPUT_FORMAT_YCBCR420 ? 2 : 1;
> +
> +		latency = (4 * crtc_state->linetime) +
> +			  (chroma_downscaling_factor *
> +			   DIV_ROUND_UP_ULL((4 * crtc_state->linetime * hscale_k * vscale_k),
> +					    1000000));
> +	} else {
> +		latency = 4 * crtc_state->linetime;
> +	}
> +
> +	return latency;
> +}
> +
>   static bool
>   skl_is_vblank_too_short(const struct intel_crtc_state *crtc_state,
>   			int wm0_lines, int latency)
> @@ -2302,6 +2332,7 @@ skl_is_vblank_too_short(const struct intel_crtc_state *crtc_state,
>   	/* FIXME missing scaler and DSC pre-fill time */

The scaler part is addressed in this patch, so this can be removed.

Regards,

Ankit

>   	return crtc_state->framestart_delay +
>   		intel_usecs_to_scanlines(adjusted_mode, latency) +
> +		scaler_prefill_latency(crtc_state) +
>   		wm0_lines >
>   		adjusted_mode->crtc_vtotal - adjusted_mode->crtc_vblank_start;
>   }