Messages in this thread | | | From | Michael Ellerman <> | Subject | Re: CPU_BIG_ENDIAN in generic code (was: Re: [PATCH v3 3/7] arch/sparc: Define config parameter CPU_BIG_ENDIAN) | Date | Tue, 30 May 2017 12:56:39 +1000 |
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Geert Uytterhoeven <geert@linux-m68k.org> writes:
> Hi Michael, > > On Mon, May 29, 2017 at 2:07 PM, Michael Ellerman <mpe@ellerman.id.au> wrote: >> Geert Uytterhoeven <geert@linux-m68k.org> writes: >>> On Tue, May 23, 2017 at 11:45 PM, Babu Moger <babu.moger@oracle.com> wrote: >>>> Found this problem while enabling queued rwlock on SPARC. >>>> The parameter CONFIG_CPU_BIG_ENDIAN is used to clear the >>>> specific byte in qrwlock structure. Without this parameter, >>>> we clear the wrong byte. Here is the code. >>>> >>>> static inline u8 *__qrwlock_write_byte(struct qrwlock *lock) >>>> { >>>> return (u8 *)lock + 3 * IS_BUILTIN(CONFIG_CPU_BIG_ENDIAN); >>>> } >>>> >>>> Define CPU_BIG_ENDIAN for SPARC to fix it. >>> >>>> --- a/arch/sparc/Kconfig >>>> +++ b/arch/sparc/Kconfig >>>> @@ -92,6 +92,10 @@ config ARCH_DEFCONFIG >>>> config ARCH_PROC_KCORE_TEXT >>>> def_bool y >>>> >>>> +config CPU_BIG_ENDIAN >>>> + bool >>>> + default y if SPARC >>> >>> Nice catch! >>> >>> Traditionally, CPU_BIG_ENDIAN and CPU_LITTLE_ENDIAN were defined only on >>> architectures that may support both. And it was checked in platform code >>> and drivers only. >>> Hence the symbol is lacking from most architectures. Heck, even >>> architectures that support both may default to one endiannes, and declare >>> only the symbol for the other endianness: >> >> I guess there's a reason we can't use __BIG_ENDIAN__ / __LITTLE_ENDIAN__ ? > > I (C/asm) code we can, in Kconfig we cannot. > > So far we tried always doing that, but a few checks for the semi-existing > Kconfig symbol crept in in generic code. Those could be replaced by the __*__ > variants, but consistently having the Kconfig symbols would be useful anyway > (e.g. to avoid building the broken-on-big-endian ISDN drivers).
Ah OK, the original mail was citing C code, but yeah I guess it would be handy in Makefiles etc.
cheers
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