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

On Thu, May 25, 2017 at 3:27 PM, Max Filippov [off-list ref] wrote:

On Wed, May 24, 2017 at 3:18 AM, Arnd Bergmann [off-list ref] wrote:

quoted

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

quoted

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

This way, we only need to add 'select CPU_BIG_ENDIAN' to the
architectures that are always big-endian, and we don't need to
change anything for the ones that have a single 'CPU_BIG_ENDIAN'
option.

The three architectures that have a 'choice' statement (mips, ppc and
sh) will have to convert, and m32r will have to replace the
option with the opposite one, which could break 'make oldconfig',
but nobody really cares about m32r any more.

Xtensa may have either endianness and for xtensa we define
CONFIG_CPU_BIG_ENDIAN or CONFIG_CPU_LITTLE_ENDIAN
in the arch/xtensa/Makefile based on the value of the compiler builtin
macro.

Also, in outside the Kconfig files there's much more instances of
__{BIG,LITTLE}_ENDIAN than CONFIG_CPU_{BIG,LITTLE}_ENDIAN:

$ git grep '__\(BIG\|LITTLE\)_ENDIAN' | wc -l
4537
$ git grep 'CONFIG_CPU_\(BIG\|LITTLE\)_ENDIAN' | wc -l
247

My understanding is that CONFIG_CPU_{BIG,LITTLE}_ENDIAN was
intended to be used only in Kconfig files, and perhaps all of its uses
outside should be replaced with __{BIG,LITTLE}_ENDIAN.

-- 
Thanks.
-- Max