Re: [Intel-gfx] [PATCH v1] drm/i915: Use intel_plane_data_rate for min_cdclk calculation

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

On Thu, Feb 20, 2020 at 05:23:47PM +0200, Stanislav Lisovskiy wrote:
> There seems to be a bit of confusing redundancy in a way, how
> plane data rate/min cdclk are calculated.
> In fact both min cdclk, pixel rate and plane data rate are all
> part of the same formula as per BSpec.
> 
> However currently we have intel_plane_data_rate, which is used
> to calculate plane data rate and which is also used in bandwidth
> calculations. However for calculating min_cdclk we have another
> piece of code, doing almost same calculation, but a bit differently
> and in a different place. However as both are actually part of same
> formula, probably would be wise to use plane data rate calculations
> as a basis anyway, thus avoiding code duplication and possible bugs
> related to this.
> 
> Another thing is that I've noticed that during min_cdclk calculations
> we account for plane scaling, while for plane data rate, we don't.
> crtc->pixel_rate seems to account only for pipe ratio, however it is
> clearly stated in BSpec that plane data rate also need to account
> plane ratio as well.
> 
> So what this commit does is:
> - Adds a plane ratio calculation to intel_plane_data_rate
> - Removes redundant calculations from skl_plane_min_cdclk which is
>   used for gen9+ and now uses intel_plane_data_rate as a basis from
>   there as well.
> 
> Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
> ---
>  .../gpu/drm/i915/display/intel_atomic_plane.c | 16 ++++++-
>  drivers/gpu/drm/i915/display/intel_sprite.c   | 46 +++++++++++--------
>  2 files changed, 41 insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_atomic_plane.c b/drivers/gpu/drm/i915/display/intel_atomic_plane.c
> index c86d7a35c816..702dfa14d112 100644
> --- a/drivers/gpu/drm/i915/display/intel_atomic_plane.c
> +++ b/drivers/gpu/drm/i915/display/intel_atomic_plane.c
> @@ -133,15 +133,27 @@ intel_plane_destroy_state(struct drm_plane *plane,
>  	kfree(plane_state);
>  }
>  
> +
> +
>  unsigned int intel_plane_data_rate(const struct intel_crtc_state *crtc_state,
>  				   const struct intel_plane_state *plane_state)
>  {
>  	const struct drm_framebuffer *fb = plane_state->hw.fb;
>  	unsigned int cpp;
> +	unsigned int src_w, src_h, dst_w, dst_h;
>  
>  	if (!plane_state->uapi.visible)
>  		return 0;
>  
> +	src_w = drm_rect_width(&plane_state->uapi.src) >> 16;
> +	src_h = drm_rect_height(&plane_state->uapi.src) >> 16;
> +	dst_w = drm_rect_width(&plane_state->uapi.dst);
> +	dst_h = drm_rect_height(&plane_state->uapi.dst);
> +
> +	/* Downscaling limits the maximum pixel rate */
> +	dst_w = min(src_w, dst_w);
> +	dst_h = min(src_h, dst_h);
> +
>  	cpp = fb->format->cpp[0];
>  
>  	/*
> @@ -153,7 +165,9 @@ unsigned int intel_plane_data_rate(const struct intel_crtc_state *crtc_state,
>  	if (fb->format->is_yuv && fb->format->num_planes > 1)
>  		cpp *= 4;
>  
> -	return cpp * crtc_state->pixel_rate;
> +	return DIV64_U64_ROUND_UP(mul_u32_u32(cpp * crtc_state->pixel_rate,
> +					      src_w * src_h),
> +				  mul_u32_u32(dst_w, dst_h));

You don't need a 64bit divisor for this.

>  }
>  
>  int intel_plane_calc_min_cdclk(struct intel_atomic_state *state,
> diff --git a/drivers/gpu/drm/i915/display/intel_sprite.c b/drivers/gpu/drm/i915/display/intel_sprite.c
> index 7abeefe8dce5..75afb78ff1b0 100644
> --- a/drivers/gpu/drm/i915/display/intel_sprite.c
> +++ b/drivers/gpu/drm/i915/display/intel_sprite.c
> @@ -330,24 +330,34 @@ bool icl_is_hdr_plane(struct drm_i915_private *dev_priv, enum plane_id plane_id)
>  }
>  
>  static void
> -skl_plane_ratio(const struct intel_crtc_state *crtc_state,
> -		const struct intel_plane_state *plane_state,
> -		unsigned int *num, unsigned int *den)
> +skl_plane_bpp_constraints(const struct intel_crtc_state *crtc_state,
> +			  const struct intel_plane_state *plane_state,
> +			  unsigned int *num, unsigned int *den)
>  {
>  	struct drm_i915_private *dev_priv = to_i915(plane_state->uapi.plane->dev);
>  	const struct drm_framebuffer *fb = plane_state->hw.fb;
> +	unsigned int cpp = fb->format->cpp[0];
> +
> +	/*
> +	 * Based on HSD#:1408715493
> +	 * NV12 cpp == 4, P010 cpp == 8
> +	 *
> +	 * FIXME what is the logic behind this?
> +	 */
> +	if (fb->format->is_yuv && fb->format->num_planes > 1)
> +		cpp *= 4;

This is ugly. I think we need a plane pixel rate instead of 
abusing the data rate as the pixel rate like this.

>  
>  	if (fb->format->cpp[0] == 8) {
>  		if (INTEL_GEN(dev_priv) >= 10 || IS_GEMINILAKE(dev_priv)) {
>  			*num = 10;
> -			*den = 8;
> +			*den = 8 * cpp;
>  		} else {
>  			*num = 9;
> -			*den = 8;
> +			*den = 8 * cpp;
>  		}
>  	} else {
>  		*num = 1;
> -		*den = 1;
> +		*den = cpp;
>  	}
>  }
>  
> @@ -355,27 +365,23 @@ static int skl_plane_min_cdclk(const struct intel_crtc_state *crtc_state,
>  			       const struct intel_plane_state *plane_state)
>  {
>  	struct drm_i915_private *dev_priv = to_i915(plane_state->uapi.plane->dev);
> -	unsigned int pixel_rate = crtc_state->pixel_rate;
> -	unsigned int src_w, src_h, dst_w, dst_h;
>  	unsigned int num, den;
> +	struct intel_plane *plane = to_intel_plane(plane_state->uapi.plane);
>  
> -	skl_plane_ratio(crtc_state, plane_state, &num, &den);
> +	skl_plane_bpp_constraints(crtc_state, plane_state, &num, &den);
>  
>  	/* two pixels per clock on glk+ */
>  	if (INTEL_GEN(dev_priv) >= 10 || IS_GEMINILAKE(dev_priv))
>  		den *= 2;
>  
> -	src_w = drm_rect_width(&plane_state->uapi.src) >> 16;
> -	src_h = drm_rect_height(&plane_state->uapi.src) >> 16;
> -	dst_w = drm_rect_width(&plane_state->uapi.dst);
> -	dst_h = drm_rect_height(&plane_state->uapi.dst);
> -
> -	/* Downscaling limits the maximum pixel rate */
> -	dst_w = min(src_w, dst_w);
> -	dst_h = min(src_h, dst_h);
> -
> -	return DIV64_U64_ROUND_UP(mul_u32_u32(pixel_rate * num, src_w * src_h),
> -				  mul_u32_u32(den, dst_w * dst_h));
> +	/*
> +	 * intel_atomic_check_planes has already been called by this
> +	 * time in intel_atomic_check, so use calculated plane
> +	 * data rate as a basis, in order not to have duplicate code.
> +	 * According to BSpec, plane data rate is anyway used as
> +	 * a basis for this calculation.
> +	 */
> +	return DIV64_U64_ROUND_UP(crtc_state->data_rate[plane->id] * num, den);
>  }
>  
>  static unsigned int
> -- 
> 2.24.1.485.gad05a3d8e5

-- 
Ville Syrjälä
Intel
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