[PATCH v8 7/7] drm/i915/dsc: Check if vblank is sufficient for dsc prefill

[Nautiyal, Ankit K]

On 1/20/2025 6:24 PM, Mitul Golani wrote:
> High refresh rate panels which may have small line times
> and vblank sizes, Check if vblank size 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.[Ankit]
> - 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]
>
> --v4:
> - Improvise hscale and vscale calculation. [Ankit]
> - Use appropriate name for number of scaler users. [Ankit]
> - Update commit message and rebase.
> - Add linetime and cdclk prefill adjustment calculation. [Ankit]
>
> --v5:
> - Update bspec link in trailer. [Ankit]
> - Correct hscale, vscale datatype. [Ankit]
> - Use intel_crtc_compute_min_cdclk. [Ankit]
>
> --v6:
> - Use cdclk_state->logical.cdclk instead of
> intel_crtc_compute_min_cdclk. [Ankit]
>
> --v7:
> - Fix linetime calculation. [Ankit]
> - Reduce redandancy use of variables. [Ankit]
> - Fix typos. [Ankit]
> - Update calculation for precision. [Ankit]
>
> Bspec: 70151
> Signed-off-by: Mitul Golani <mitulkumar.ajitkumar.golani at intel.com>
> ---
>   drivers/gpu/drm/i915/display/skl_watermark.c | 32 +++++++++++++++++++-
>   1 file changed, 31 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/display/skl_watermark.c b/drivers/gpu/drm/i915/display/skl_watermark.c
> index 448d320e0d47..89e8da70c333 100644
> --- a/drivers/gpu/drm/i915/display/skl_watermark.c
> +++ b/drivers/gpu/drm/i915/display/skl_watermark.c
> @@ -2310,6 +2310,36 @@ cdclk_prefill_adjustment(const struct intel_crtc_state *crtc_state)
>   				   2 * cdclk_state->logical.cdclk));
>   }
>   
> +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 linetime = DIV_ROUND_UP(1000 * crtc_state->hw.adjusted_mode.htotal,
> +				    crtc_state->hw.adjusted_mode.clock);
> +	u32 dsc_prefill_latency;

Need to initialize this.


> +	int num_scaler_users = hweight32(scaler_state->scaler_users);
> +	int chroma_downscaling_factor =
> +		crtc_state->output_format == INTEL_OUTPUT_FORMAT_YCBCR420 ? 2 : 1;
> +	u64 hscale_k, vscale_k;
> +

These should be local to the loop below.

With above fixed:

Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal at intel.com>

> +	if (!crtc_state->dsc.compression_enable || !num_scaler_users)
> +		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++) {
> +		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);
> +	}
> +
> +	dsc_prefill_latency *= cdclk_prefill_adjustment(crtc_state);
> +
> +	return intel_usecs_to_scanlines(&crtc_state->hw.adjusted_mode, dsc_prefill_latency);
> +}
> +
>   static int
>   scaler_prefill_latency(const struct intel_crtc_state *crtc_state)
>   {
> @@ -2350,10 +2380,10 @@ skl_is_vblank_too_short(const struct intel_crtc_state *crtc_state,
>   	const struct drm_display_mode *adjusted_mode =
>   		&crtc_state->hw.adjusted_mode;
>   
> -	/* FIXME missing DSC pre-fill time */
>   	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;
>   }