RE: [PATCH 6.12.y-cip 02/11] bitfield: Add non-constant field_{prep,get}() helpers

I believe you get build warning duplicate definitions

[1]
https://lore.kernel.org/cip-dev/177941154371.3955.14567547508285219672@330cfa3079ca/


Cheers,
Biju

> -----Original Message-----
> From: Lad Prabhakar <[email protected]>
> Sent: 29 June 2026 23:53
> To: [email protected]; Nobuhiro Iwamatsu <[email protected]>; Pavel Machek
> <[email protected]>
> Cc: Biju Das <[email protected]>
> Subject: [PATCH 6.12.y-cip 02/11] bitfield: Add non-constant field_{prep,get}() helpers
> 
> From: Geert Uytterhoeven <[email protected]>
> 
> commit c1c6ab80b25c8db1e2ef5ae3ac8075d2c242ae13 upstream.
> 
> The existing FIELD_{GET,PREP}() macros are limited to compile-time constants.  However, it is very common
> to prepare or extract bitfield elements where the bitfield mask is not a compile-time constant.
> 
> To avoid this limitation, the AT91 clock driver and several other drivers already have their own non-
> const field_{prep,get}() macros.
> Make them available for general use by adding them to <linux/bitfield.h>, and improve them slightly:
>   1. Avoid evaluating macro parameters more than once,
>   2. Replace "ffs() - 1" by "__ffs()",
>   3. Support 64-bit use on 32-bit architectures,
>   4. Wire field_{get,prep}() to FIELD_{GET,PREP}() when mask is
>      actually constant.
> 
> This is deliberately not merged into the existing FIELD_{GET,PREP}() macros, as people expressed the
> desire to keep stricter variants for increased safety, or for performance critical paths.
> 
> Yury: use __mask withing new macros.
> 
> Signed-off-by: Geert Uytterhoeven <[email protected]>
> Acked-by: Alexandre Belloni <[email protected]>
> Acked-by: Jonathan Cameron <[email protected]>
> Acked-by: Crt Mori <[email protected]>
> Acked-by: Nuno Sá <[email protected]>
> Acked-by: Richard Genoud <[email protected]>
> Reviewed-by: Andy Shevchenko <[email protected]>
> Reviewed-by: Yury Norov (NVIDIA) <[email protected]>
> Signed-off-by: Yury Norov (NVIDIA) <[email protected]>
> Signed-off-by: Lad Prabhakar <[email protected]>
> ---
>  include/linux/bitfield.h | 59 ++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 59 insertions(+)
> 
> diff --git a/include/linux/bitfield.h b/include/linux/bitfield.h index 3346c6009c2ce..22bbef382bb9c
> 100644
> --- a/include/linux/bitfield.h
> +++ b/include/linux/bitfield.h
> @@ -17,6 +17,7 @@
>   * FIELD_{GET,PREP} macros take as first parameter shifted mask
>   * from which they extract the base mask and shift amount.
>   * Mask must be a compilation time constant.
> + * field_{get,prep} are variants that take a non-const mask.
>   *
>   * Example:
>   *
> @@ -240,4 +241,62 @@ __MAKE_OP(64)
>  #undef __MAKE_OP
>  #undef ____MAKE_OP
> 
> +#define __field_prep(mask, val)						\
> +	({								\
> +		__auto_type __mask = (mask);				\
> +		typeof(__mask) __val = (val);				\
> +		unsigned int __shift = BITS_PER_TYPE(__mask) <= 32 ?	\
> +				       __ffs(__mask) : __ffs64(__mask);	\
> +		(__val << __shift) & __mask;				\
> +	})
> +
> +#define __field_get(mask, reg)						\
> +	({								\
> +		__auto_type __mask = (mask);				\
> +		typeof(__mask) __reg =  (reg);				\
> +		unsigned int __shift = BITS_PER_TYPE(__mask) <= 32 ?	\
> +				       __ffs(__mask) : __ffs64(__mask);	\
> +		(__reg & __mask) >> __shift;				\
> +	})
> +
> +/**
> + * field_prep() - prepare a bitfield element
> + * @mask: shifted mask defining the field's length and position, must be
> + *        non-zero
> + * @val:  value to put in the field
> + *
> + * Return: field value masked and shifted to its final destination
> + *
> + * field_prep() masks and shifts up the value.  The result should be
> + * combined with other fields of the bitfield using logical OR.
> + * Unlike FIELD_PREP(), @mask is not limited to a compile-time constant.
> + * Typical usage patterns are a value stored in a table, or calculated
> +by
> + * shifting a constant by a variable number of bits.
> + * If you want to ensure that @mask is a compile-time constant, please
> +use
> + * FIELD_PREP() directly instead.
> + */
> +#define field_prep(mask, val)						\
> +	(__builtin_constant_p(mask) ? __FIELD_PREP(mask, val, "field_prep: ") \
> +				    : __field_prep(mask, val))
> +
> +/**
> + * field_get() - extract a bitfield element
> + * @mask: shifted mask defining the field's length and position, must be
> + *        non-zero
> + * @reg:  value of entire bitfield
> + *
> + * Return: extracted field value
> + *
> + * field_get() extracts the field specified by @mask from the
> + * bitfield passed in as @reg by masking and shifting it down.
> + * Unlike FIELD_GET(), @mask is not limited to a compile-time constant.
> + * Typical usage patterns are a value stored in a table, or calculated
> +by
> + * shifting a constant by a variable number of bits.
> + * If you want to ensure that @mask is a compile-time constant, please
> +use
> + * FIELD_GET() directly instead.
> + */
> +#define field_get(mask, reg)						\
> +	(__builtin_constant_p(mask) ? __FIELD_GET(mask, reg, "field_get: ") \
> +				    : __field_get(mask, reg))
> +
>  #endif
> --
> 2.43.0