On Tue, Jan 18, 2022 at 11:23:42AM +0200, Ville Syrjala wrote:
> From: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
>
> We are currently computing the relative data rates as
> src_size * scale_factor where scale_factor is src_size / dst_size.
> Thus relative data rate is src_size * src_size / dst_size,
> which is just utter nonsense. What we really seem to want is
> just a reasonable estimate on how much data will be fetched
> which is just src_size. So let's do that instead.
>
> Signed-off-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
Omg, how could it stay like this all the time?
I actually had similar question, but thought that there just might
be again some magical/empirical heuristics behind this.
Need to challenge more anything, which can't be explained with
BSpec formulas or by common sense...
Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@xxxxxxxxx>
> ---
> drivers/gpu/drm/i915/intel_pm.c | 63 ++-------------------------------
> 1 file changed, 2 insertions(+), 61 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index 9a9d4acb2988..e8fb56f288b4 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -4373,55 +4373,6 @@ void skl_pipe_ddb_get_hw_state(struct intel_crtc *crtc,
> intel_display_power_put(dev_priv, power_domain, wakeref);
> }
>
> -/*
> - * Determines the downscale amount of a plane for the purposes of watermark calculations.
> - * The bspec defines downscale amount as:
> - *
> - * """
> - * Horizontal down scale amount = maximum[1, Horizontal source size /
> - * Horizontal destination size]
> - * Vertical down scale amount = maximum[1, Vertical source size /
> - * Vertical destination size]
> - * Total down scale amount = Horizontal down scale amount *
> - * Vertical down scale amount
> - * """
> - *
> - * Return value is provided in 16.16 fixed point form to retain fractional part.
> - * Caller should take care of dividing & rounding off the value.
> - */
> -static uint_fixed_16_16_t
> -skl_plane_downscale_amount(const struct intel_crtc_state *crtc_state,
> - const struct intel_plane_state *plane_state)
> -{
> - struct drm_i915_private *dev_priv = to_i915(crtc_state->uapi.crtc->dev);
> - u32 src_w, src_h, dst_w, dst_h;
> - uint_fixed_16_16_t fp_w_ratio, fp_h_ratio;
> - uint_fixed_16_16_t downscale_h, downscale_w;
> -
> - if (drm_WARN_ON(&dev_priv->drm,
> - !intel_wm_plane_visible(crtc_state, plane_state)))
> - return u32_to_fixed16(0);
> -
> - /*
> - * Src coordinates are already rotated by 270 degrees for
> - * the 90/270 degree plane rotation cases (to match the
> - * GTT mapping), hence no need to account for rotation here.
> - *
> - * n.b., src is 16.16 fixed point, dst is whole integer.
> - */
> - 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);
> -
> - fp_w_ratio = div_fixed16(src_w, dst_w);
> - fp_h_ratio = div_fixed16(src_h, dst_h);
> - downscale_w = max_fixed16(fp_w_ratio, u32_to_fixed16(1));
> - downscale_h = max_fixed16(fp_h_ratio, u32_to_fixed16(1));
> -
> - return mul_fixed16(downscale_w, downscale_h);
> -}
> -
> struct dbuf_slice_conf_entry {
> u8 active_pipes;
> u8 dbuf_mask[I915_MAX_PIPES];
> @@ -4932,10 +4883,7 @@ skl_plane_relative_data_rate(const struct intel_crtc_state *crtc_state,
> {
> struct intel_plane *plane = to_intel_plane(plane_state->uapi.plane);
> const struct drm_framebuffer *fb = plane_state->hw.fb;
> - u32 data_rate;
> - u32 width = 0, height = 0;
> - uint_fixed_16_16_t down_scale_amount;
> - u64 rate;
> + int width, height;
>
> if (!plane_state->uapi.visible)
> return 0;
> @@ -4961,14 +4909,7 @@ skl_plane_relative_data_rate(const struct intel_crtc_state *crtc_state,
> height /= 2;
> }
>
> - data_rate = width * height;
> -
> - down_scale_amount = skl_plane_downscale_amount(crtc_state, plane_state);
> -
> - rate = mul_round_up_u32_fixed16(data_rate, down_scale_amount);
> -
> - rate *= fb->format->cpp[color_plane];
> - return rate;
> + return width * height * fb->format->cpp[color_plane];
> }
>
> static u64
> --
> 2.32.0
>
