linux-kernel - Re: [PATCH v2 08/16] bitfield: Simplify __BF_FIELD_CHECK

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Message-ID: <20251217102618.0000465f@huawei.com>
Date: Wed, 17 Dec 2025 10:26:18 +0000
From: Jonathan Cameron <jonathan.cameron@...wei.com>
To: <david.laight.linux@...il.com>
CC: Yury Norov <yury.norov@...il.com>, Rasmus Villemoes
	<linux@...musvillemoes.dk>, <linux-kernel@...r.kernel.org>,
	<linux-usb@...r.kernel.org>, Geert Uytterhoeven <geert+renesas@...der.be>,
	Alexandre Belloni <alexandre.belloni@...tlin.com>, Crt Mori
	<cmo@...exis.com>, Richard Genoud <richard.genoud@...tlin.com>, "Andy
 Shevchenko" <andriy.shevchenko@...el.com>, Luo Jie <quic_luoj@...cinc.com>,
	Peter Zijlstra <peterz@...radead.org>, Jakub Kicinski <kuba@...nel.org>,
	<netdev@...r.kernel.org>, "David S . Miller" <davem@...emloft.net>, "Mika
 Westerberg" <mika.westerberg@...ux.intel.com>, Andreas Noever
	<andreas.noever@...il.com>, Yehezkel Bernat <YehezkelShB@...il.com>, Nicolas
 Frattaroli <nicolas.frattaroli@...labora.com>
Subject: Re: [PATCH v2 08/16] bitfield: Simplify __BF_FIELD_CHECK_REG()

On Fri, 12 Dec 2025 19:37:13 +0000
david.laight.linux@...il.com wrote:

> From: David Laight <david.laight.linux@...il.com>
> 
> Simplify the check for 'reg' being large enough to hold 'mask' using
> sizeof (reg) rather than a convoluted scheme to generate an unsigned
> type the same size as 'reg'.
> 
> Signed-off-by: David Laight <david.laight.linux@...il.com>
Hi David,

Just one really trivial comment inline. Feel free to ignore.

Jonathan

> ---
> @@ -75,8 +59,8 @@
>  	})
>  
>  #define __BF_FIELD_CHECK_REG(mask, reg, pfx)				\
> -	BUILD_BUG_ON_MSG(__bf_cast_unsigned(mask, mask) >		\
> -			 __bf_cast_unsigned(reg, ~0ull),		\
> +	BUILD_BUG_ON_MSG((mask) + 0U + 0UL + 0ULL >			\
> +			 ~0ULL >> (64 - 8 * sizeof (reg)),		\

Trivial.  sizeof(reg) is much more comment syntax in kernel code.

>  			 pfx "type of reg too small for mask")
>  
>  #define __BF_FIELD_CHECK(mask, reg, val, pfx)				\