CPU_BIG_ENDIAN in generic code (was: Re: [PATCH v3 3/7] arch/sparc: Define config parameter CPU_BIG_ENDIAN)
From: Geert Uytterhoeven <geert@linux-m68k.org>
Date: 2017-05-24 09:59:30
Also in:
linux-arch, linux-serial, lkml, sparclinux
On Tue, May 23, 2017 at 11:45 PM, Babu Moger [off-list ref] 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.quoted hunk
--- 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:
--- arch/alpha ---
--- arch/arc ---arch/arc/Kconfig:config CPU_BIG_ENDIAN
--- arch/arm ---arch/arm/mm/Kconfig:config CPU_BIG_ENDIAN
--- arch/arm64 ---arch/arm64/Kconfig:config CPU_BIG_ENDIAN
--- arch/blackfin ---
--- arch/c6x ---arch/c6x/Kconfig:config CPU_BIG_ENDIAN
--- arch/cris ---
--- arch/frv ---
--- arch/h8300 ---
--- arch/hexagon ---
--- arch/ia64 ---
--- arch/Kconfig ---
--- arch/m32r ---arch/m32r/Kconfig:config CPU_LITTLE_ENDIAN
--- arch/m68k ---
--- arch/metag ---
--- arch/microblaze ---
--- arch/mips ---arch/mips/Kconfig:config CPU_BIG_ENDIAN arch/mips/Kconfig:config CPU_LITTLE_ENDIAN
--- arch/mn10300 ---
--- arch/nios2 ---
--- arch/openrisc ---
--- arch/parisc ---
--- arch/powerpc ---arch/powerpc/platforms/Kconfig.cputype:config CPU_BIG_ENDIAN arch/powerpc/platforms/Kconfig.cputype:config CPU_LITTLE_ENDIAN
--- arch/s390 ---arch/s390/Kconfig:config CPU_BIG_ENDIAN
--- arch/score ---
--- arch/sh ---arch/sh/Kconfig.cpu:config CPU_LITTLE_ENDIAN arch/sh/Kconfig.cpu:config CPU_BIG_ENDIAN
--- arch/sparc ---
--- arch/tile ---
--- arch/um ---
--- arch/unicore32 ---
--- arch/x86 ---
--- arch/xtensa ---
However, there are already a few users in generic code, which are thus
broken on many platforms:
drivers/of/base.c
drivers/of/fdt.c
drivers/tty/serial/earlycon.c
drivers/tty/serial/serial_core.c
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?
Gr{oetje,eeting}s,
Geert