Re: [PATCH 1/2] drm/i915: Use DIV_ROUND_CLOSEST() to calculate dot/vco

[Jesse Barnes <jbarnes@virtuousgeek.org>]

On Mon, 14 Oct 2013 14:50:30 +0300
ville.syrjala@linux.intel.com wrote:

> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> Rounding down when calculating the dot/vco frequencies doesn't make much
> sense. Round to closest should give slightly nicer answers.
> 
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/intel_display.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index fbd028e..baa6ef6 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -329,8 +329,8 @@ static void vlv_clock(int refclk, intel_clock_t *clock)
>  {
>  	clock->m = clock->m1 * clock->m2;
>  	clock->p = clock->p1 * clock->p2;
> -	clock->vco = refclk * clock->m / clock->n;
> -	clock->dot = clock->vco / clock->p;
> +	clock->vco = DIV_ROUND_CLOSEST(refclk * clock->m, clock->n);
> +	clock->dot = DIV_ROUND_CLOSEST(clock->vco, clock->p);
>  }
>  
>  /**
> @@ -430,8 +430,8 @@ static void pineview_clock(int refclk, intel_clock_t *clock)
>  {
>  	clock->m = clock->m2 + 2;
>  	clock->p = clock->p1 * clock->p2;
> -	clock->vco = refclk * clock->m / clock->n;
> -	clock->dot = clock->vco / clock->p;
> +	clock->vco = DIV_ROUND_CLOSEST(refclk * clock->m, clock->n);
> +	clock->dot = DIV_ROUND_CLOSEST(clock->vco, clock->p);
>  }
>  
>  static uint32_t i9xx_dpll_compute_m(struct dpll *dpll)
> @@ -443,8 +443,8 @@ static void i9xx_clock(int refclk, intel_clock_t *clock)
>  {
>  	clock->m = i9xx_dpll_compute_m(clock);
>  	clock->p = clock->p1 * clock->p2;
> -	clock->vco = refclk * clock->m / (clock->n + 2);
> -	clock->dot = clock->vco / clock->p;
> +	clock->vco = DIV_ROUND_CLOSEST(refclk * clock->m, clock->n + 2);
> +	clock->dot = DIV_ROUND_CLOSEST(clock->vco, clock->p);
>  }
>  
>  #define INTELPllInvalid(s)   do { /* DRM_DEBUG(s); */ return false; } while (0)

Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>

-- 
Jesse Barnes, Intel Open Source Technology Center
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