linux-kernel - Re: [PATCH v4 1/4] bitfield: Drop underscores from macro parameters

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Message-ID: <aPJwtZSMgZLDzxH8@yury>
Date: Fri, 17 Oct 2025 12:37:09 -0400
From: Yury Norov <yury.norov@...il.com>
To: Geert Uytterhoeven <geert+renesas@...der.be>
Cc: Michael Turquette <mturquette@...libre.com>,
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Subject: Re: [PATCH v4 1/4] bitfield: Drop underscores from macro parameters

On Fri, Oct 17, 2025 at 12:54:09PM +0200, Geert Uytterhoeven wrote:
> There is no need to prefix macro parameters with underscores.
> Remove the underscores.
> 
> Suggested-by: David Laight <david.laight.linux@...il.com>
> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
> ---
> v4:
>   - Update recently introduced FIELD_MODIFY() macro,
> 
> v3:
>   - New.
> ---
>  include/linux/bitfield.h | 106 +++++++++++++++++++--------------------
>  1 file changed, 53 insertions(+), 53 deletions(-)
> 
> diff --git a/include/linux/bitfield.h b/include/linux/bitfield.h
> index 5355f8f806a97974..7ff817bdae19b468 100644
> --- a/include/linux/bitfield.h
> +++ b/include/linux/bitfield.h
> @@ -60,68 +60,68 @@
>  
>  #define __bf_cast_unsigned(type, x)	((__unsigned_scalar_typeof(type))(x))
>  
> -#define __BF_FIELD_CHECK(_mask, _reg, _val, _pfx)			\
> +#define __BF_FIELD_CHECK(mask, reg, val, pfx)				\
>  	({								\
> -		BUILD_BUG_ON_MSG(!__builtin_constant_p(_mask),		\
> -				 _pfx "mask is not constant");		\
> -		BUILD_BUG_ON_MSG((_mask) == 0, _pfx "mask is zero");	\
> -		BUILD_BUG_ON_MSG(__builtin_constant_p(_val) ?		\
> -				 ~((_mask) >> __bf_shf(_mask)) &	\
> -					(0 + (_val)) : 0,		\
> -				 _pfx "value too large for the field"); \
> -		BUILD_BUG_ON_MSG(__bf_cast_unsigned(_mask, _mask) >	\
> -				 __bf_cast_unsigned(_reg, ~0ull),	\
> -				 _pfx "type of reg too small for mask"); \
> -		__BUILD_BUG_ON_NOT_POWER_OF_2((_mask) +			\
> -					      (1ULL << __bf_shf(_mask))); \
> +		BUILD_BUG_ON_MSG(!__builtin_constant_p(mask),		\
> +				 pfx "mask is not constant");		\
> +		BUILD_BUG_ON_MSG((mask) == 0, pfx "mask is zero");	\
> +		BUILD_BUG_ON_MSG(__builtin_constant_p(val) ?		\
> +				 ~((mask) >> __bf_shf(mask)) &	\
> +					(0 + (val)) : 0,		\
> +				 pfx "value too large for the field"); \
> +		BUILD_BUG_ON_MSG(__bf_cast_unsigned(mask, mask) >	\
> +				 __bf_cast_unsigned(reg, ~0ull),	\
> +				 pfx "type of reg too small for mask"); \
> +		__BUILD_BUG_ON_NOT_POWER_OF_2((mask) +			\
> +					      (1ULL << __bf_shf(mask))); \
>  	})

Hi Geert,

Thanks for the series!

I agree that underscored parameters are excessive. But fixing them has
a side effect of wiping the history, which is a bad thing.

I would prefer to save a history over following a rule that seemingly
is not written down. Let's keep this untouched for now, and if there
will be a need to move the code, we can drop underscores as well.

Meanwhile you (and David) can propose a corresponding rule in
coding-style.rst and a checkpatch warning. That way we at least will
stop merging a new code of that style.

Thanks,
Yury