Re: CPU_BIG_ENDIAN in generic code (was: Re: [PATCH v3 3/7] arch/sparc: Define config parameter CPU_BIG_ENDIAN)

[Babu Moger]

On 5/24/2017 10:09 AM, Arnd Bergmann wrote:
> On Wed, May 24, 2017 at 4:45 PM, Babu Moger <babu.moger@xxxxxxxxxx> wrote:
> > On 5/24/2017 5:18 AM, Arnd Bergmann wrote:
> > > On Wed, May 24, 2017 at 11:59 AM, Geert Uytterhoeven
> > > <geert@xxxxxxxxxxxxxx> wrote:
> > > > On Tue, May 23, 2017 at 11:45 PM, Babu Moger <babu.moger@xxxxxxxxxx>
> > > > wrote:
> > > > include/asm-generic/qrwlock.h is also generic, but depends on the
> > > > architecture to select ARCH_USE_QUEUED_RWLOCKS, which only very few do
> > > > (x86, and now sparc).
> > > >
> > > > I guess the time is ripe for adding (both) symbols to all architectures?
> > > Good idea. I think we can do most of this by adding a few lines to
> > > arch/Kconfig:
> > >
> > > config CPU_BIG_ENDIAN
> > >           bool
> > >
> > > config CPU_LITTLE_ENDIAN
> > >          def_bool !CPU_BIG_ENDIAN
> > I noticed that even x86 does not define CPU_LITTLE_ENDIAN.  Strange.
> There is no architecture-independent code that tests for
> CONFIG_CPU_LITTLE_ENDIAN, unlike CONFIG_CPU_BIG_ENDIAN,
> so that's not very suprising.

Ok. Thanks
> > With this code all the architecture will default to
> > CONFIG_CPU_LITTLE_ENDIAN.
> What I meant is that we have to 'select CPU_BIG_ENDIAN' on all architectures
> that actually are big-endian:
Ok. Sure.
> These are all configurable:
> $ git grep -l linux/byteorder/big_endian.h | xargs grep -l
> linux/byteorder/little_endian.h
> arch/arc/include/uapi/asm/byteorder.h
> arch/arm/include/uapi/asm/byteorder.h
> arch/arm64/include/uapi/asm/byteorder.h
> arch/c6x/include/uapi/asm/byteorder.h
> arch/m32r/include/uapi/asm/byteorder.h
> arch/microblaze/include/uapi/asm/byteorder.h
> arch/mips/include/uapi/asm/byteorder.h
> arch/powerpc/include/uapi/asm/byteorder.h
> arch/sh/include/uapi/asm/byteorder.h
> arch/tile/include/uapi/asm/byteorder.h
>
> These are always big-endian:
> $ git grep -l linux/byteorder/big_endian.h | xargs grep -L
> linux/byteorder/little_endian.h
> arch/avr32/include/uapi/asm/byteorder.h
> arch/frv/include/uapi/asm/byteorder.h
> arch/m68k/include/uapi/asm/byteorder.h
> arch/openrisc/include/uapi/asm/byteorder.h
> arch/parisc/include/uapi/asm/byteorder.h
> arch/s390/include/uapi/asm/byteorder.h
> arch/sparc/include/uapi/asm/byteorder.h
>
> And these are always little-endian:
> arch/alpha/include/uapi/asm/byteorder.h
> arch/blackfin/include/uapi/asm/byteorder.h
> arch/cris/include/uapi/asm/byteorder.h
> arch/hexagon/include/uapi/asm/byteorder.h
> arch/ia64/include/uapi/asm/byteorder.h
> arch/metag/include/uapi/asm/byteorder.h
> arch/mn10300/include/uapi/asm/byteorder.h
> arch/score/include/uapi/asm/byteorder.h
> arch/unicore32/include/uapi/asm/byteorder.h
> arch/x86/include/uapi/asm/byteorder.h
>
> So if we 'select CPU_BIG_ENDIAN' from avr32, frv, m68k, openrisc, parisc,
> s390 and sparc, this covers all the fixed-endian architectures, and the
> other ones are those that already have either CPU_BIG_ENDIAN
> as a 'bool' option, or both as a 'choice'.
Ok.  Great details. I think I have all the details required for the 
first version.  Will post it soon. Thanks

> > I can make it as a separate patch. But I can only test SPARC and little bit
> > of x86. Is that ok?
> I think that's ok.
>
>          Arnd