Re: [PATCH v2] drm/i915/skl: Skip remaining dividers when deviation is 0

[Daniel Vetter <daniel@ffwll.ch>]

On Fri, Jun 26, 2015 at 06:34:29PM +0100, Damien Lespiau wrote:
> We can't improve a 0 deviation, so when we find such a divider, skip the
> remaining ones they won't be better.
> 
> This short-circuit the search for 34 of the 373 test frequencies in the
> corresponding i-g-t test (tools/skl_compute_wrpll)
> 
> v2: Place the short-circuiting code in skl_compute_wrpll() (Paulo)
> 
> (I'm sure nobody will notice the spurious removal of a blank line)
> 
> Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
> Suggested-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
> Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>

Queued for -next, thanks for the patch.
-Daniel

> ---
>  drivers/gpu/drm/i915/intel_ddi.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
> index f6b3ccc..42c1487 100644
> --- a/drivers/gpu/drm/i915/intel_ddi.c
> +++ b/drivers/gpu/drm/i915/intel_ddi.c
> @@ -1149,7 +1149,6 @@ static void skl_wrpll_try_divider(struct skl_wrpll_context *ctx,
>  		ctx->dco_freq = dco_freq;
>  		ctx->p = divider;
>  	}
> -
>  }
>  
>  static void skl_wrpll_get_multipliers(unsigned int p,
> @@ -1315,9 +1314,17 @@ skl_ddi_calculate_wrpll(int clock /* in Hz */,
>  						      dco_central_freq[dco],
>  						      dco_freq,
>  						      p);
> +				/*
> +				 * Skip the remaining dividers if we're sure to
> +				 * have found the definitive divider, we can't
> +				 * improve a 0 deviation.
> +				 */
> +				if (ctx.min_deviation == 0)
> +					goto skip_remaining_dividers;
>  			}
>  		}
>  
> +skip_remaining_dividers:
>  		/*
>  		 * If a solution is found with an even divider, prefer
>  		 * this one.
> -- 
> 2.1.0
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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