Re: [PATCH v3 10/34] xen/riscv: introduce bitops.h

[Oleksii <oleksii.kurochko@xxxxxxxxx>]

> > > 
> > > > > Also you want to make sure asm-generic/bitops/bitops-bits.h
> > > > > is
> > > > > really in use here, or else an arch overriding / not using
> > > > > that
> > > > > header may end up screwed.
> > > > I am not really understand what do you mean. Could you please
> > > > explain a
> > > > little bit more.
> > > 
> > > Whichever type you use here, it needs to be in sync with
> > > BITOP_BITS_PER_WORD. Hence you want to include the _local_
> > > bitops-
> > > bits.h
> > > here, such that in case of an inconsistent override by an arch
> > > the
> > > compiler would complain about the two differring #define-s. (IOW
> > > an
> > > arch overriding BITOP_BITS_PER_WORD cannot re-use this header as-
> > > is.)
> > > 
> > > The same may, btw, be true for others of the new headers you add
> > > -
> > > the
> > > same #include would therefore be needed there as well.
> > Now it clear to me.
> > 
> > 
> > It seems like BITOP_BITS_PER_WORD, BITOP_MASK, BITOP_WORD, and
> > BITS_PER_BYTE are defined in {arm, ppc,
> > riscv}/include/asm/bitops.h.
> > I expected that any architecture planning to use asm-
> > generic/bitops/bitops-bits.h would include it at the beginning of
> > <arch>/include/asm/bitops.h, similar to what is done for RISC-V:
> >    #ifndef _ASM_RISCV_BITOPS_H
> >    #define _ASM_RISCV_BITOPS_H
> >    
> >    #include <asm/system.h>
> >    
> >    #include <asm-generic/bitops/bitops-bits.h>
> >    ...
> > 
> > But in this case, to allow architecture overrides macros, it is
> > necessary to update asm-generic/bitops/bitops-bits.h:
> >     #ifndef BITOP_BITS_PER_WORD
> >     #define BITOP_BITS_PER_WORD     32
> >     #endif
> >    ...
> > Therefore,  if an architecture needs to override something, it will
> > add
> > #define ... before #include <asm-generic/bitops/bitops-bits.h>.
> > 
> > Does it make sense?
> 
> Sure. But then the arch also needs to provide a corresponding typedef
> (and bitops-bits.h the fallback one), for use wherever you use any of
> those #define-s.
Which one typedef is needed to provide?
<asm-generic/bitops/bitops-bits.h> contains only macros.


~ Oleksii