[Intel-gfx] [PATCH 57/89] drm/i915: Rewrite ABS_DIFF() in a safer manner

[Jani Nikula]

On Thu, 04 Sep 2014, Damien Lespiau <damien.lespiau at intel.com> wrote:
> The new version of the macro does a few things better:
>   - protect the arguments,
>   - only evaluate the arguments once,
>   - check that the arguments are of the same type,
>
> Change LC_FREQ_2K to be a unsigned 64bit constant and removed the '()'
> from the caller as a result.
>
> Signed-off-by: Damien Lespiau <damien.lespiau at intel.com>

Reviewed-by: Jani Nikula <jani.nikula at intel.com>

Can be picked up for dinq separate from this series, right?


> ---
>  drivers/gpu/drm/i915/intel_ddi.c | 14 +++++++++-----
>  1 file changed, 9 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
> index 64eda53..ba1103f 100644
> --- a/drivers/gpu/drm/i915/intel_ddi.c
> +++ b/drivers/gpu/drm/i915/intel_ddi.c
> @@ -460,7 +460,7 @@ intel_ddi_get_crtc_encoder(struct drm_crtc *crtc)
>  }
>  
>  #define LC_FREQ 2700
> -#define LC_FREQ_2K (LC_FREQ * 2000)
> +#define LC_FREQ_2K U64_C(LC_FREQ * 2000)
>  
>  #define P_MIN 2
>  #define P_MAX 64
> @@ -472,7 +472,11 @@ intel_ddi_get_crtc_encoder(struct drm_crtc *crtc)
>  #define VCO_MIN 2400
>  #define VCO_MAX 4800
>  
> -#define ABS_DIFF(a, b) ((a > b) ? (a - b) : (b - a))
> +#define abs_diff(a, b) ({			\
> +	typeof(a) __a = (a);			\
> +	typeof(b) __b = (b);			\
> +	(void) (&__a == &__b);			\
> +	__a > __b ? (__a - __b) : (__b - __a); })
>  
>  struct wrpll_rnp {
>  	unsigned p, n2, r2;
> @@ -582,9 +586,9 @@ static void wrpll_update_rnp(uint64_t freq2k, unsigned budget,
>  	 */
>  	a = freq2k * budget * p * r2;
>  	b = freq2k * budget * best->p * best->r2;
> -	diff = ABS_DIFF((freq2k * p * r2), (LC_FREQ_2K * n2));
> -	diff_best = ABS_DIFF((freq2k * best->p * best->r2),
> -			     (LC_FREQ_2K * best->n2));
> +	diff = abs_diff(freq2k * p * r2, LC_FREQ_2K * n2);
> +	diff_best = abs_diff(freq2k * best->p * best->r2,
> +			     LC_FREQ_2K * best->n2);
>  	c = 1000000 * diff;
>  	d = 1000000 * diff_best;
>  
> -- 
> 1.8.3.1
>
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-- 
Jani Nikula, Intel Open Source Technology Center