[Intel-gfx] [PATCH 24/40] drm/i915: Fix threshold for choosing 32 vs. 64 precisions for VLV DDL values

[Paulo Zanoni]

2014-06-27 20:04 GMT-03:00  <ville.syrjala at linux.intel.com>:
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
>
> The DDL registers can hold 7bit numbers. Make the most of those seven
> bits by adjusting the threshold where we switch between the 64 vs. 32
> precision multipliers.
>
> Also we compute 'entries' to make the decision about precision, and then
> we recompute the same value to calculate the actual drain latency. Just
> use the already calculate 'entries' there.

Just an addition: don't we also want to WARN in case "entires < 64"
(or in case the final result exceeds 7 bits, which is equivalent)?
Could be a separate patch too.

With or without that: Reviewed-by: Paulo Zanoni <paulo.r.zanoni at intel.com>

>
> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> ---
>  drivers/gpu/drm/i915/intel_pm.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index 9413184..3aa7959 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -1252,15 +1252,14 @@ static bool vlv_compute_drain_latency(struct drm_device *dev,
>         pixel_size = crtc->primary->fb->bits_per_pixel / 8;     /* BPP */
>
>         entries = (clock / 1000) * pixel_size;
> -       *plane_prec_mult = (entries > 256) ?
> +       *plane_prec_mult = (entries > 128) ?
>                 DRAIN_LATENCY_PRECISION_64 : DRAIN_LATENCY_PRECISION_32;
> -       *plane_dl = (64 * (*plane_prec_mult) * 4) / ((clock / 1000) *
> -                                                    pixel_size);
> +       *plane_dl = (64 * (*plane_prec_mult) * 4) / entries;
>
>         entries = (clock / 1000) * 4;   /* BPP is always 4 for cursor */
> -       *cursor_prec_mult = (entries > 256) ?
> +       *cursor_prec_mult = (entries > 128) ?
>                 DRAIN_LATENCY_PRECISION_64 : DRAIN_LATENCY_PRECISION_32;
> -       *cursor_dl = (64 * (*cursor_prec_mult) * 4) / ((clock / 1000) * 4);
> +       *cursor_dl = (64 * (*cursor_prec_mult) * 4) / entries;
>
>         return true;
>  }
> --
> 1.8.5.5
>
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-- 
Paulo Zanoni