[PATCH 01/12] drm/i915/skl_watermark: Fix the scaling factor for chroma subsampling

[Golani, Mitulkumar Ajitkumar]

> -----Original Message-----
> From: Nautiyal, Ankit K <ankit.k.nautiyal at intel.com>
> Sent: 07 August 2025 16:46
> To: intel-gfx at lists.freedesktop.org; intel-xe at lists.freedesktop.org
> Cc: ville.syrjala at linux.intel.com; jani.nikula at linux.intel.com; Golani,
> Mitulkumar Ajitkumar <mitulkumar.ajitkumar.golani at intel.com>; Nautiyal,
> Ankit K <ankit.k.nautiyal at intel.com>
> Subject: [PATCH 01/12] drm/i915/skl_watermark: Fix the scaling factor for
> chroma subsampling
> 
> The Bspec:70151, mentions Chroma subsampling is a 2x downscale operation.
> This means that the downscale factor is 2 in each direction.
> So correct the downscaling factor to 4.
> 
> Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal at intel.com>
> ---
>  drivers/gpu/drm/i915/display/skl_watermark.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/skl_watermark.c
> b/drivers/gpu/drm/i915/display/skl_watermark.c
> index def5150231a4..df586509a742 100644
> --- a/drivers/gpu/drm/i915/display/skl_watermark.c
> +++ b/drivers/gpu/drm/i915/display/skl_watermark.c
> @@ -2185,7 +2185,7 @@ dsc_prefill_latency(const struct intel_crtc_state
> *crtc_state)
>  				    crtc_state->hw.adjusted_mode.clock);
>  	int num_scaler_users = hweight32(scaler_state->scaler_users);
>  	int chroma_downscaling_factor =
> -		crtc_state->output_format ==
> INTEL_OUTPUT_FORMAT_YCBCR420 ? 2 : 1;
> +		crtc_state->output_format ==
> INTEL_OUTPUT_FORMAT_YCBCR420 ? 4 : 1;
>  	u32 dsc_prefill_latency = 0;
> 
>  	if (!crtc_state->dsc.compression_enable || @@ -2228,7 +2228,7 @@
> scaler_prefill_latency(const struct intel_crtc_state *crtc_state)
>  		u64 hscale_k = max(1000, mul_u32_u32(scaler_state-
> >scalers[0].hscale, 1000) >> 16);
>  		u64 vscale_k = max(1000, mul_u32_u32(scaler_state-
> >scalers[0].vscale, 1000) >> 16);
>  		int chroma_downscaling_factor =
> -			crtc_state->output_format ==
> INTEL_OUTPUT_FORMAT_YCBCR420 ? 2 : 1;
> +			crtc_state->output_format ==
> INTEL_OUTPUT_FORMAT_YCBCR420 ? 4 : 1;
>  		int latency;

Reviewed-by: Mitul Golani <mitulkumar.ajitkumar.golani at intel.com>

> 
>  		latency = DIV_ROUND_UP_ULL((4 * linetime * hscale_k *
> vscale_k *
> --
> 2.45.2