[RFC PATCH v4 02/42] drm: Add helper for conversion from signed-magnitude

[Melissa Wen]

On 02/26, Harry Wentland wrote:
> CTM values are defined as signed-magnitude values. Add
> a helper that converts from CTM signed-magnitude fixed
> point value to the twos-complement value used by
> drm_fixed.
> 
> Signed-off-by: Harry Wentland <harry.wentland at amd.com>
> ---
>  include/drm/drm_fixed.h | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/include/drm/drm_fixed.h b/include/drm/drm_fixed.h
> index 0c9f917a4d4b..cb842ba80ddd 100644
> --- a/include/drm/drm_fixed.h
> +++ b/include/drm/drm_fixed.h
> @@ -78,6 +78,24 @@ static inline u32 dfixed_div(fixed20_12 A, fixed20_12 B)
>  #define DRM_FIXED_EPSILON	1LL
>  #define DRM_FIXED_ALMOST_ONE	(DRM_FIXED_ONE - DRM_FIXED_EPSILON)
>  
> +/**
> + * @drm_sm2fixp
> + *
> + * Convert a 1.31.32 signed-magnitude fixed point to 32.32
> + * 2s-complement fixed point
> + *
> + * @return s64 2s-complement fixed point
> + */
> +static inline s64 drm_sm2fixp(__u64 a)
> +{
> +	if ((a & (1LL << 63))) {
> +		return -(a & 0x7fffffffffffffffll);
Hi Harry,

Can we have a #define macro for this constant? ^
Other than that, LGTM. You can add my r-b to the next version.

Thanks,

Melissa
> +	} else {
> +		return a;
> +	}
> +
> +}
> +
>  static inline s64 drm_int2fixp(int a)
>  {
>  	return ((s64)a) << DRM_FIXED_POINT;
> -- 
> 2.44.0
>