Re: [Intel-gfx] [PATCH 05/13] drm/i915/intel_cdclk: Add vdsc with bigjoiner constraints on min_cdlck

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Fri, May 12, 2023 at 11:54:09AM +0530, Ankit Nautiyal wrote:
> As per Bsepc:49259, Bigjoiner BW check puts restriction on the
> compressed bpp for a given CDCLK, pixelclock in cases where
> Bigjoiner + DSC are used.
> 
> Currently compressed bpp is computed first, and it is ensured that
> the bpp will work at least with the max CDCLK freq.
> 
> Since the CDCLK is computed later, lets account for Bigjoiner BW
> check while calculating Min CDCLK.
> 
> Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_cdclk.c | 49 ++++++++++++++++++----
>  1 file changed, 42 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_cdclk.c b/drivers/gpu/drm/i915/display/intel_cdclk.c
> index 6bed75f1541a..3532640c5027 100644
> --- a/drivers/gpu/drm/i915/display/intel_cdclk.c
> +++ b/drivers/gpu/drm/i915/display/intel_cdclk.c
> @@ -2520,6 +2520,46 @@ static int intel_planes_min_cdclk(const struct intel_crtc_state *crtc_state)
>  	return min_cdclk;
>  }
>  
> +static int intel_vdsc_min_cdclk(const struct intel_crtc_state *crtc_state)
> +{
> +	struct intel_crtc *crtc = to_intel_crtc(crtc_state->uapi.crtc);
> +	struct drm_i915_private *i915 = to_i915(crtc->base.dev);
> +	int min_cdclk = 0;
> +
> +	/*
> +	 * When we decide to use only one VDSC engine, since
> +	 * each VDSC operates with 1 ppc throughput, pixel clock
> +	 * cannot be higher than the VDSC clock (cdclk)
> +	 */
> +	if (!crtc_state->dsc.dsc_split)
> +		min_cdclk = max(min_cdclk, (int)crtc_state->pixel_rate);
> +
> +	if (crtc_state->bigjoiner_pipes) {
> +		/*
> +		 * According to Bigjoiner bw check:
> +		 * compressed_bpp <= PPC * CDCLK * Big joiner Interface bits / Pixel clock
> +		 *
> +		 * We have already computed compressed_bpp, so now compute the min CDCLK that
> +		 * is required to support this compressed_bpp.
> +		 *
> +		 * => CDCLK >= compressed_bpp * Pixel clock / (PPC * Bigjoiner Interface bits)
> +		 *
> +		 * Since Num of pipes joined = 2, and PPC = 2 with bigjoiner
> +		 * => CDCLK >= compressed_bpp * pixel_rate  / Bigjoiner Interface bits
> +		 *
> +		 * #TODO Bspec mentions to account for FEC overhead while using pixel clock.
> +		 * Check if we need to use FEC overhead in the above calculations.
> +		 */
> +		int bigjoiner_interface_bits = DISPLAY_VER(i915) > 13 ? 36 : 24;
> +		int min_cdclk_bj = crtc_state->dsc.compressed_bpp * crtc_state->pixel_rate /
> +				   bigjoiner_interface_bits;

pixel_rate is the downscale adjusted thing, so it doesn't seem
like the correct thing to use here.

Hmm. Assuming that the single VDSC engine really throttles the entire
pipe to 1 PPC then we should probably account for the 1 vs. 2 PPC
difference in *_plane_min_cdclk() and intel_pixel_rate_to_cdclk()
directly. Currently all of those assume 2 PPC.

> +
> +		min_cdclk = max(min_cdclk, min_cdclk_bj);
> +	}
> +
> +	return min_cdclk;
> +}
> +
>  int intel_crtc_compute_min_cdclk(const struct intel_crtc_state *crtc_state)
>  {
>  	struct drm_i915_private *dev_priv =
> @@ -2591,13 +2631,8 @@ int intel_crtc_compute_min_cdclk(const struct intel_crtc_state *crtc_state)
>  	/* Account for additional needs from the planes */
>  	min_cdclk = max(intel_planes_min_cdclk(crtc_state), min_cdclk);
>  
> -	/*
> -	 * When we decide to use only one VDSC engine, since
> -	 * each VDSC operates with 1 ppc throughput, pixel clock
> -	 * cannot be higher than the VDSC clock (cdclk)
> -	 */
> -	if (crtc_state->dsc.compression_enable && !crtc_state->dsc.dsc_split)
> -		min_cdclk = max(min_cdclk, (int)crtc_state->pixel_rate);
> +	if (crtc_state->dsc.compression_enable)
> +		min_cdclk = max(min_cdclk, intel_vdsc_min_cdclk(crtc_state));
>  
>  	/*
>  	 * HACK. Currently for TGL/DG2 platforms we calculate
> -- 
> 2.25.1

-- 
Ville Syrjälä
Intel