On 5/24/2017 10:09 AM, Arnd Bergmann wrote:

On Wed, May 24, 2017 at 4:45 PM, Babu Moger [off-list ref] wrote:

quoted

On 5/24/2017 5:18 AM, Arnd Bergmann wrote:

quoted

On Wed, May 24, 2017 at 11:59 AM, Geert Uytterhoeven
[off-list ref] wrote:

quoted

On Tue, May 23, 2017 at 11:45 PM, Babu Moger [off-list ref]
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

quoted

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

quoted

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