linux-kernel - Re: [PATCH 1/3] bits: introduce fixed-type genmasks

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Date: Wed, 24 Jan 2024 09:58:26 +0200
From: Jani Nikula <jani.nikula@...ux.intel.com>
To: Lucas De Marchi <lucas.demarchi@...el.com>, Yury Norov
 <yury.norov@...il.com>
Cc: linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org, Andy
 Shevchenko <andriy.shevchenko@...ux.intel.com>,
 intel-xe@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org
Subject: Re: [PATCH 1/3] bits: introduce fixed-type genmasks

On Tue, 23 Jan 2024, Lucas De Marchi <lucas.demarchi@...el.com> wrote:
> From: Yury Norov <yury.norov@...il.com>
>
> Generalize __GENMASK() to support different types, and implement
> fixed-types versions of GENMASK() based on it. The fixed-type version
> allows more strict checks to the min/max values accepted, which is
> useful for defining registers like implemented by i915 and xe drivers
> with their REG_GENMASK*() macros.

Mmh, the commit message says the fixed-type version allows more strict
checks, but none are actually added. GENMASK_INPUT_CHECK() remains the
same.

Compared to the i915 and xe versions, this is more lax now. You could
specify GENMASK_U32(63,32) without complaints.


BR,
Jani.

>
> Signed-off-by: Yury Norov <yury.norov@...il.com>
> ---
>  include/linux/bitops.h |  1 -
>  include/linux/bits.h   | 22 ++++++++++++----------
>  2 files changed, 12 insertions(+), 11 deletions(-)
>
> diff --git a/include/linux/bitops.h b/include/linux/bitops.h
> index 2ba557e067fe..1db50c69cfdb 100644
> --- a/include/linux/bitops.h
> +++ b/include/linux/bitops.h
> @@ -15,7 +15,6 @@
>  #  define aligned_byte_mask(n) (~0xffUL << (BITS_PER_LONG - 8 - 8*(n)))
>  #endif
>  
> -#define BITS_PER_TYPE(type)	(sizeof(type) * BITS_PER_BYTE)
>  #define BITS_TO_LONGS(nr)	__KERNEL_DIV_ROUND_UP(nr, BITS_PER_TYPE(long))
>  #define BITS_TO_U64(nr)		__KERNEL_DIV_ROUND_UP(nr, BITS_PER_TYPE(u64))
>  #define BITS_TO_U32(nr)		__KERNEL_DIV_ROUND_UP(nr, BITS_PER_TYPE(u32))
> diff --git a/include/linux/bits.h b/include/linux/bits.h
> index 7c0cf5031abe..cb94128171b2 100644
> --- a/include/linux/bits.h
> +++ b/include/linux/bits.h
> @@ -6,6 +6,8 @@
>  #include <vdso/bits.h>
>  #include <asm/bitsperlong.h>
>  
> +#define BITS_PER_TYPE(type)	(sizeof(type) * BITS_PER_BYTE)
> +
>  #define BIT_MASK(nr)		(UL(1) << ((nr) % BITS_PER_LONG))
>  #define BIT_WORD(nr)		((nr) / BITS_PER_LONG)
>  #define BIT_ULL_MASK(nr)	(ULL(1) << ((nr) % BITS_PER_LONG_LONG))
> @@ -30,16 +32,16 @@
>  #define GENMASK_INPUT_CHECK(h, l) 0
>  #endif
>  
> -#define __GENMASK(h, l) \
> -	(((~UL(0)) - (UL(1) << (l)) + 1) & \
> -	 (~UL(0) >> (BITS_PER_LONG - 1 - (h))))
> -#define GENMASK(h, l) \
> -	(GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))
> +#define __GENMASK(t, h, l) \
> +	(GENMASK_INPUT_CHECK(h, l) + \
> +	 (((t)~0ULL - ((t)(1) << (l)) + 1) & \
> +	 ((t)~0ULL >> (BITS_PER_TYPE(t) - 1 - (h)))))
>  
> -#define __GENMASK_ULL(h, l) \
> -	(((~ULL(0)) - (ULL(1) << (l)) + 1) & \
> -	 (~ULL(0) >> (BITS_PER_LONG_LONG - 1 - (h))))
> -#define GENMASK_ULL(h, l) \
> -	(GENMASK_INPUT_CHECK(h, l) + __GENMASK_ULL(h, l))
> +#define GENMASK(h, l)		__GENMASK(unsigned long,  h, l)
> +#define GENMASK_ULL(h, l)	__GENMASK(unsigned long long, h, l)
> +#define GENMASK_U8(h, l)	__GENMASK(u8,  h, l)
> +#define GENMASK_U16(h, l)	__GENMASK(u16, h, l)
> +#define GENMASK_U32(h, l)	__GENMASK(u32, h, l)
> +#define GENMASK_U64(h, l)	__GENMASK(u64, h, l)
>  
>  #endif	/* __LINUX_BITS_H */

-- 
Jani Nikula, Intel