On Wed, 4 Oct 2017 11:49:57 -0700, Matthias Kaehlcke wrote:
> Hi Joe,
>
> El Wed, Oct 04, 2017 at 11:07:19AM -0700 Joe Perches ha dit:
>
> > On Tue, 2017-10-03 at 13:05 -0700, Matthias Kaehlcke wrote:
> > > nfp_eth_set_bit_config() is marked as __always_inline to allow gcc to
> > > identify the 'mask' parameter as known to be constant at compile time,
> > > which is required to use the FIELD_GET() macro.
> > >
> > > The forced inlining does the trick for gcc, but for kernel builds with
> > > clang it results in undefined symbols:
> >
> > Can't you use local different FIELD_PREP/FIELD_GET macros
> > with a different name without the BUILD_BUG tests?
> >
> > i.e.:
> >
> > #define NFP_FIELD_PREP(_mask, _val) \
> > ({ \
> > ((typeof(_mask))(_val) << __bf_shf(_mask)) & (_mask); \
> > })
> >
> > #define NFP_FIELD_GET(_mask, _reg) \
> > ({ \
> > (typeof(_mask))(((_reg) & (_mask)) >> __bf_shf(_mask)); \
> > })
> >
> > Then the __always_inline can be removed from
> > nfp_eth_set_bit_config too.
>
> Thanks for the suggestion. This seems a viable alternative if David
> and the NFP owners can live without the extra checking provided by
> __BF_FIELD_CHECK.
The reason the __BF_FIELD_CHECK refuses to compile non-constant masks
is that it will require runtime ffs on the mask, which is potentially
costly. I would also feel quite stupid adding those macros to the nfp
driver, given that I specifically created the bitfield.h header to not
have to reimplement these in every driver I write/maintain.
Can you please test the patch I provided in the other reply?
