Re: [PATCH v2 3/9] bitops: Introduce a more generic BITMASK macro

Joe Perches
2013-10-17T02:59:14Z

On Wed, 2013-10-16 at 10:56 -0400, Chen, Gong wrote:
> GENMASK is used to create a contiguous bitmask([hi:lo]). It is
> implemented twice in current kernel. One is in EDAC driver, the other
> is in SiS/XGI FB driver. Move it to a more generic place for other
> usage.
[]
> diff --git a/include/linux/bitops.h b/include/linux/bitops.h
[]
> @@ -10,6 +10,14 @@
> #define BITS_TO_LONGS(nr) DIV_ROUND_UP(nr, BITS_PER_BYTE * sizeof(long))
> #endif
>
> +/*
> + * Create a contiguous bitmask starting at bit position @l and ending at
> + * position @h. For example
> + * GENMASK_ULL(39, 21) gives us the 64bit vector 0x000000ffffe00000.

ull

> + */
> +#define GENMASK(h, l) (((U32_C(1) << ((h) - (l) + 1)) - 1) << (l))
> +#define GENMASK_ULL(h, l) (((U64_C(1) << ((h) - (l) + 1)) - 1) << (l))

Maybe add a

BUILD_BUG_ON(__builtin_constant_p(l) && __builtin_constant_p(h) && \
(h) < (l))