[PATCH v4 7/7] drm/i915/dsc: Check if vblank is sufficient for dsc prefill

[Nautiyal, Ankit K]

On 1/8/2025 6:05 PM, Mitul Golani wrote:
> Check if vblank is sufficient for dsc prefill latency.
>
> --v2:
> - Consider chroma downscaling factor in latency calculation. [Ankit]
> - Replace with appropriate function name.
>
> --v3:
> - Remove FIXME tag.[Ankit]
> - Replace Ycbcr444 to Ycbcr420.[Anit]
> - Correct precision. [Ankit]
> - Use some local valiables like linetime_factor and latency to
> adjust precision.
> - Declare latency to 0 initially to avoid returning any garbage values.
> - Account for second scaler downscaling factor as well. [Ankit]
>
> Signed-off-by: Mitul Golani <mitulkumar.ajitkumar.golani at intel.com>
> ---
>   drivers/gpu/drm/i915/display/skl_watermark.c | 37 ++++++++++++++++++++
>   1 file changed, 37 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/display/skl_watermark.c b/drivers/gpu/drm/i915/display/skl_watermark.c
> index fe91854e456c..d275ec687748 100644
> --- a/drivers/gpu/drm/i915/display/skl_watermark.c
> +++ b/drivers/gpu/drm/i915/display/skl_watermark.c
> @@ -2292,6 +2292,42 @@ static int icl_build_plane_wm(struct intel_crtc_state *crtc_state,
>   	return 0;
>   }
>   
> +static int
> +dsc_prefill_latency(const struct intel_crtc_state *crtc_state)
> +{
> +	const struct intel_crtc_scaler_state *scaler_state =
> +						&crtc_state->scaler_state;
> +	int latency = 0;
> +	int count = hweight32(scaler_state->scaler_users);
> +	long long hscale_k[2] = {1, 1};
> +	long long vscale_k[2] = {1, 1};
> +
> +	if (!crtc_state->dsc.compression_enable)
> +		return latency;
> +
> +	for (int i = 0; i < count; i++) {
> +		hscale_k[i] = mul_u32_u32(scaler_state->scalers[i].hscale, 1000) >> 16;
> +		vscale_k[i] = mul_u32_u32(scaler_state->scalers[i].vscale, 1000) >> 16;
> +	}
> +
> +	if (count) {
> +		int chroma_downscaling_factor =
> +			crtc_state->output_format == INTEL_OUTPUT_FORMAT_YCBCR420 ? 2 : 1;
> +		long long total_scaling_factor;
> +		int linetime_factor = DIV_ROUND_UP(15 * crtc_state->linetime, 10);
> +
> +		total_scaling_factor  = DIV_ROUND_UP_ULL(hscale_k[0] * vscale_k[0], 1000000);

I think this might end up being 0.

Consider hscale and vscale to be 0.5 each. hscale_k and vscale_k will be 
500 each.

total_scaling_factor will become 500*500/ 10,00,000 or 2,50,000 
/10,00,000 = 0.

I think you should compute latency for scaler 0 and then if there is 
another scaler, multiply it with the total scaling factor for scaler 1.

Regards,

Ankit


> +
> +		if (count > 1)
> +			total_scaling_factor *= DIV_ROUND_UP_ULL(hscale_k[1] * vscale_k[1],
> +								 1000000);
> +
> +		latency = total_scaling_factor * linetime_factor * chroma_downscaling_factor;
> +	}
> +
> +	return latency;
> +}
> +
>   static int
>   scaler_prefill_latency(const struct intel_crtc_state *crtc_state)
>   {
> @@ -2333,6 +2369,7 @@ skl_is_vblank_too_short(const struct intel_crtc_state *crtc_state,
>   	return crtc_state->framestart_delay +
>   		intel_usecs_to_scanlines(adjusted_mode, latency) +
>   		scaler_prefill_latency(crtc_state) +
> +		dsc_prefill_latency(crtc_state) +
>   		wm0_lines >
>   		adjusted_mode->crtc_vtotal - adjusted_mode->crtc_vblank_start;
>   }