Messages in this thread | | | Subject | Re: [PATCH] bitfield: add constant field preparation macros | From | John Garry <> | Date | Mon, 15 Oct 2018 09:53:36 +0100 |
| |
On 12/10/2018 20:45, Johannes Berg wrote: > From: Johannes Berg <johannes.berg@intel.com> > > John Garry requested to be able to use FIELD_PREP() and friends > in constant initializers, but we cannot completely switch all of > the current assertions to BUILD_BUG_ON_ZERO(). >
Thanks for this.
> So instead of this, add __FIELD_PREP() which is suitable in such > contexts, and also add __{u,le,be}{16,32,64}encode_bits() like > the existing versions without underscores, but again suitable in > constant contexts. > > Requested-by: John Garry <john.garry@huawei.com> > Signed-off-by: Johannes Berg <johannes.berg@intel.com> > --- > include/linux/bitfield.h | 34 ++++++++++++++++++++++++++++++++++ > 1 file changed, 34 insertions(+) > > diff --git a/include/linux/bitfield.h b/include/linux/bitfield.h > index 3f1ef4450a7c..245dfb47d201 100644 > --- a/include/linux/bitfield.h > +++ b/include/linux/bitfield.h > @@ -63,6 +63,14 @@ > (1ULL << __bf_shf(_mask))); \ > }) > > +#define __BF_CHECK_POW2(n) BUILD_BUG_ON_ZERO(((n) & ((n) - 1)) != 0) > + > +#define __BF_FIELD_CHECK_CONST(_mask, _reg, _val) \ > + (BUILD_BUG_ON_ZERO((_mask) == 0) + \ > + BUILD_BUG_ON_ZERO(~((_mask) >> __bf_shf(_mask)) & (_val)) + \ > + BUILD_BUG_ON_ZERO((_mask) > (typeof(_reg))~0ull) + \ > + __BF_CHECK_POW2((_mask) + (1ULL << __bf_shf(_mask)))) > + > /** > * FIELD_FIT() - check if value fits in the field > * @_mask: shifted mask defining the field's length and position > @@ -90,6 +98,21 @@ > ((typeof(_mask))(_val) << __bf_shf(_mask)) & (_mask); \ > }) > > +/** > + * __FIELD_PREP() - prepare a constant bitfield element
My impression is that the name prefix - '__' - tells little about the function. If you agree, how about even CFIELD_PREP() or FIELD_PREP_CONST() or similar? I preper the latter, but becomes rather long.
> + * @_mask: shifted mask defining the field's length and position > + * @_val: value to put in the field > + * > + * __FIELD_PREP() masks and shifts up the value. The result should > + * be combined with other fields of the bitfield using local OR.
should this be 'logical OR', or indeed 'bitwise OR'?
> + * > + * This version is suitable for use in a pure constant context, e.g. > + * a constant initializer. > + */ > +#define __FIELD_PREP(_mask, _val) \ > + ((typeof(_mask))__BF_FIELD_CHECK_CONST(_mask, 0ULL, _val) + \ > + (((typeof(_mask))(_val) << __bf_shf(_mask)) & (_mask))) > + > /** > * FIELD_GET() - extract a bitfield element > * @_mask: shifted mask defining the field's length and position > @@ -150,4 +173,15 @@ __MAKE_OP(64) > #undef __MAKE_OP > #undef ____MAKE_OP > > +#define __encode_bits(w, v, field) __FIELD_PREP((u##w)(field), v) > +#define __u16_encode_bits(v, field) __encode_bits(16, v, field) > +#define __le16_encode_bits(v, field) cpu_to_le16(__encode_bits(16, v, field)) > +#define __be16_encode_bits(v, field) cpu_to_be16(__encode_bits(16, v, field)) > +#define __u32_encode_bits(v, field) __encode_bits(32, v, field) > +#define __le32_encode_bits(v, field) cpu_to_le32(__encode_bits(32, v, field)) > +#define __be32_encode_bits(v, field) cpu_to_be32(__encode_bits(32, v, field)) > +#define __u64_encode_bits(v, field) __encode_bits(64, v, field) > +#define __le64_encode_bits(v, field) cpu_to_le64(__encode_bits(64, v, field)) > +#define __be64_encode_bits(v, field) cpu_to_be64(__encode_bits(64, v, field)) > + > #endif >
Thanks again, John
| |