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

Hi Biju,

> -----Original Message-----
> From: Biju Das <[email protected]>
> Sent: 30 June 2026 10:40
> To: Prabhakar Mahadev Lad <[email protected]>; cip-
> [email protected]; Nobuhiro Iwamatsu
> <[email protected]>; Pavel Machek <[email protected]>
> Subject: RE: [PATCH 6.12.y-cip 02/11] bitfield: Add non-constant
> field_{prep,get}() helpers
> 
> I believe you get build warning duplicate definitions
>
Thanks for the pointer, SND_USB was not enabled so I didn’t see this issue.

I will send a v2 while using it locally. As done elsewhere.

Cheers,
Prabhakar
 
> [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