Re: [PATCH 3/9] bitmap: Use FIELD_PREP() in expansion of FIELD_PREP_WM16()

Nicolas Frattaroli
2025-12-11T12:51:18Z

On Wednesday, 10 December 2025 21:59:15 Central European Standard Time David Laight wrote:
> On Wed, 10 Dec 2025 20:18:30 +0100
> Nicolas Frattaroli <nicolas.frattaroli@collabora.com> wrote:
>
> > On Tuesday, 9 December 2025 11:03:07 Central European Standard Time david.laight.linux@gmail.com wrote:
> > > From: David Laight <david.laight.linux@gmail.com>
> > >
> > > Instead of directly expanding __BF_FIELD_CHECK() (which really ought
> > > not be used outside bitfield) and open-coding the generation of the
> > > masked value, just call FIELD_PREP() and add an extra check for
> > > the mask being at most 16 bits.
> > >
> > > Signed-off-by: David Laight <david.laight.linux@gmail.com>
> > > ---
> > > include/linux/hw_bitfield.h | 17 ++++++++---------
> > > 1 file changed, 8 insertions(+), 9 deletions(-)
> > >
> > > diff --git a/include/linux/hw_bitfield.h b/include/linux/hw_bitfield.h
> > > index df202e167ce4..d7f21b60449b 100644
> > > --- a/include/linux/hw_bitfield.h
> > > +++ b/include/linux/hw_bitfield.h
> > > @@ -23,15 +23,14 @@
> > > * register, a bit in the lower half is only updated if the corresponding bit
> > > * in the upper half is high.
> > > */
> > > -#define FIELD_PREP_WM16(_mask, _val) \
> > > - ({ \
> > > - typeof(_val) __val = _val; \
> > > - typeof(_mask) __mask = _mask; \
> > > - __BF_FIELD_CHECK(__mask, ((u16)0U), __val, \
> > > - "HWORD_UPDATE: "); \
> > > - (((typeof(__mask))(__val) << __bf_shf(__mask)) & (__mask)) | \
> > > - ((__mask) << 16); \
> > > - })
> > > +#define FIELD_PREP_WM16(mask, val) \
> > > +({ \
> > > + __auto_type _mask = mask; \
> > > + u32 _val = FIELD_PREP(_mask, val); \
> > > + BUILD_BUG_ON_MSG(_mask > 0xffffu, \
> > > + "FIELD_PREP_WM16: mask too large"); \
> > > + _val | (_mask << 16); \
> > > +})
> > >
> > > /**
> > > * FIELD_PREP_WM16_CONST() - prepare a constant bitfield element with a mask in
> > >
> >
> > This breaks the build for at least one driver that uses
> > FIELD_PREP_WM16, namely phy-rockchip-emmc.c:
>
> Not in my allmodconfig build.
> ...
> > pcie-dw-rockchip.c is similarly broken by this change, except
> > without the superfluous wrapper:
>
> That one did get built.

I build with clang 21.1.6 for arm64, in case that's any help.
I don't see how pcie-dw-rockchip.c built for you if FIELD_PREP
and FIELD_PREP_WM16 have conflicting symbol names?

>
> The problem is that FIELD_PREP_WM16() needs to use different 'local'
> variables than FIELD_PREP().
> The 'proper' fix is to use unique names (as min() and max() do), but that
> makes the whole thing unreadable and is best avoided unless nesting is
> likely.
> In this case s/mask/wm16_mask/ and s/val/wm16_val/ might be best.
>
> David
>
>