Re: CPU_BIG_ENDIAN in generic code (was: Re: [PATCH v3 3/7] arch/sparc: Define config parameter CPU_BIG_ENDIAN)
From: Babu Moger
Date: Wed May 24 2017 - 10:46:29 EST
Arnd,
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:
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:
--- 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?
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.
With this code all the architecture will default to
CONFIG_CPU_LITTLE_ENDIAN.
I can make it as a separate patch. But I can only test SPARC and little
bit of x86.
Is that ok?
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.
Arnd