linux-kernel - Re: [PATCH v3 2/3] bits: Introduce fixed-type BIT

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Message-ID: <ZcZYhZbLyzSXX8PU@yury-ThinkPad>
Date: Fri, 9 Feb 2024 08:53:25 -0800
From: Yury Norov <yury.norov@...il.com>
To: Lucas De Marchi <lucas.demarchi@...el.com>
Cc: linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Jani Nikula <jani.nikula@...ux.intel.com>,
	intel-xe@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org,
	Jani Nikula <jani.nikula@...el.com>
Subject: Re: [PATCH v3 2/3] bits: Introduce fixed-type BIT

On Wed, Feb 07, 2024 at 11:45:20PM -0800, Lucas De Marchi wrote:
> Implement fixed-type BIT() to help drivers add stricter checks, like was
> done for GENMASK.
> 
> Signed-off-by: Lucas De Marchi <lucas.demarchi@...el.com>
> Acked-by: Jani Nikula <jani.nikula@...el.com>

So I get v1 from Jan.23 in my mailbox, and this one is v3. Did I miss
a v2? Anyways, please bear my reviewed-by from v1 for this patch.

Thanks,
Yury

> ---
>  include/linux/bits.h | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/include/linux/bits.h b/include/linux/bits.h
> index bd56f32de44e..811846ce110e 100644
> --- a/include/linux/bits.h
> +++ b/include/linux/bits.h
> @@ -24,12 +24,16 @@
>  #define GENMASK_INPUT_CHECK(h, l) \
>  	(BUILD_BUG_ON_ZERO(__builtin_choose_expr( \
>  		__is_constexpr((l) > (h)), (l) > (h), 0)))
> +#define BIT_INPUT_CHECK(type, b) \
> +	((BUILD_BUG_ON_ZERO(__builtin_choose_expr( \
> +		__is_constexpr(b), (b) >= BITS_PER_TYPE(type), 0))))
>  #else
>  /*
>   * BUILD_BUG_ON_ZERO is not available in h files included from asm files,
>   * disable the input check if that is the case.
>   */
>  #define GENMASK_INPUT_CHECK(h, l) 0
> +#define BIT_INPUT_CHECK(type, b) 0
>  #endif
>  
>  /*
> @@ -54,4 +58,17 @@
>  #define GENMASK_U32(h, l)	__GENMASK(u32, h, l)
>  #define GENMASK_U64(h, l)	__GENMASK(u64, h, l)
>  
> +/*
> + * Fixed-type variants of BIT(), with additional checks like __GENMASK().  The
> + * following examples generate compiler warnings due to shift-count-overflow:
> + *
> + * - BIT_U8(8)
> + * - BIT_U32(-1)
> + * - BIT_U32(40)
> + */
> +#define BIT_U8(b)		((u8)(BIT_INPUT_CHECK(u8, b) + BIT(b)))
> +#define BIT_U16(b)		((u16)(BIT_INPUT_CHECK(u16, b) + BIT(b)))
> +#define BIT_U32(b)		((u32)(BIT_INPUT_CHECK(u32, b) + BIT(b)))
> +#define BIT_U64(b)		((u64)(BIT_INPUT_CHECK(u64, b) + BIT(b)))
> +
>  #endif	/* __LINUX_BITS_H */
> -- 
> 2.43.0