On Tue, Mar 31, 2026 at 08:00:04PM -0300, Luiz Angelo Daros de Luca wrote:
> Some hardware stores logical fields split across multiple registers,
> requiring partial values to be reassembled using shifts and masks.
>
> Add FIELD_WIDTH(), a helper that returns the number of contiguous bits
> covered by a bitfield mask. This allows callers to determine how much a
> partial value needs to be shifted when reconstructing a field.
>
> This complements FIELD_MAX() and FIELD_FIT(), and avoids reimplementing
> bit counting logic in drivers.
>
> Signed-off-by: Luiz Angelo Daros de Luca <luizluca@gmail.com>
> ---
> include/linux/bitfield.h | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> diff --git a/include/linux/bitfield.h b/include/linux/bitfield.h
> index 54aeeef1f0ec..8d6c1c309c3b 100644
> --- a/include/linux/bitfield.h
> +++ b/include/linux/bitfield.h
> @@ -111,6 +111,19 @@
> (typeof(_mask))((_mask) >> __bf_shf(_mask)); \
> })
>
> +/**
> + * FIELD_WIDTH() - return the width of a bitfield
> + * @_mask: shifted mask defining the field's length and position
> + *
> + * Returns the number of contiguous bits covered by @_mask.
> + * This corresponds to the bit width of FIELD_MAX(@_mask).
> + */
> +#define FIELD_WIDTH(_mask) \
Please no underscored names unless necessary.
> + ({ \
> + __BF_FIELD_CHECK(_mask, 0ULL, 0ULL, "FIELD_WIDTH: "); \
> + __bf_shf(~FIELD_MAX(_mask)); \
> + })
I believe, this should be:
#define FIELD_WIDTH(mask) ({ \
__BF_FIELD_CHECK_MASK(mask, 0ULL, "FIELD_WIDTH: "); \
HWEIGHT(mask); \
})
Thanks,
Yury
> +
> /**
> * FIELD_FIT() - check if value fits in the field
> * @_mask: shifted mask defining the field's length and position
>
> --
> 2.53.0
>