On Mon, May 27, 2019 at 05:34:11PM +0900, Masahiro Yamada wrote: > BIT(), GENMASK(), etc. are useful to define register bits of hardware. > However, low-level code is often written in assembly, where they are > not available due to the hard-coded 1UL, 0UL. > > In fact, in-kernel headers such as arch/arm64/include/asm/sysreg.h > use _BITUL() instead of BIT() so that the register bit macros are > available in assembly. > > Using macros in include/uapi/linux/const.h have two reasons: > > [1] For use in uapi headers > We should use underscore-prefixed variants for user-space. > > [2] For use in assembly code > Since _BITUL() does not use hard-coded 1UL, it can be used as an > alternative of BIT(). > > For [2], it is pretty easy to change BIT() etc. for use in assembly. > > This allows to replace _BUTUL() in kernel headers with BIT(). > > Signed-off-by: Masahiro Yamada <[email protected]> > --- > > include/linux/bits.h | 17 ++++++++++------- > 1 file changed, 10 insertions(+), 7 deletions(-)
Acked-by: Will Deacon <[email protected]> Will
