linux-kernel - Re: [PATCH v2 cmpxchg 11/13] csky: Emulate one-byte cmpxchg

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Date: Sat, 11 May 2024 14:42:17 +0800
From: Guo Ren <guoren@...nel.org>
To: "Paul E. McKenney" <paulmck@...nel.org>
Cc: linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org, elver@...gle.com, 
	akpm@...ux-foundation.org, tglx@...utronix.de, peterz@...radead.org, 
	dianders@...omium.org, pmladek@...e.com, arnd@...db.de, 
	torvalds@...ux-foundation.org, kernel-team@...a.com, 
	Yujie Liu <yujie.liu@...el.com>, linux-csky@...r.kernel.org
Subject: Re: [PATCH v2 cmpxchg 11/13] csky: Emulate one-byte cmpxchg

On Thu, May 2, 2024 at 7:01 AM Paul E. McKenney <paulmck@...nel.org> wrote:
>
> Use the new cmpxchg_emu_u8() to emulate one-byte cmpxchg() on csky.
>
> [ paulmck: Apply kernel test robot feedback. ]
> [ paulmck: Drop two-byte support per Arnd Bergmann feedback. ]
>
> Co-developed-by: Yujie Liu <yujie.liu@...el.com>
> Signed-off-by: Yujie Liu <yujie.liu@...el.com>
> Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
> Tested-by: Yujie Liu <yujie.liu@...el.com>
> Cc: Guo Ren <guoren@...nel.org>
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: <linux-csky@...r.kernel.org>
> ---
>  arch/csky/Kconfig               |  1 +
>  arch/csky/include/asm/cmpxchg.h | 10 ++++++++++
>  2 files changed, 11 insertions(+)
>
> diff --git a/arch/csky/Kconfig b/arch/csky/Kconfig
> index d3ac36751ad1f..5479707eb5d10 100644
> --- a/arch/csky/Kconfig
> +++ b/arch/csky/Kconfig
> @@ -37,6 +37,7 @@ config CSKY
>         select ARCH_INLINE_SPIN_UNLOCK_BH if !PREEMPTION
>         select ARCH_INLINE_SPIN_UNLOCK_IRQ if !PREEMPTION
>         select ARCH_INLINE_SPIN_UNLOCK_IRQRESTORE if !PREEMPTION
> +       select ARCH_NEED_CMPXCHG_1_EMU
>         select ARCH_WANT_FRAME_POINTERS if !CPU_CK610 && $(cc-option,-mbacktrace)
>         select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
>         select COMMON_CLK
> diff --git a/arch/csky/include/asm/cmpxchg.h b/arch/csky/include/asm/cmpxchg.h
> index 916043b845f14..db6dda47184e4 100644
> --- a/arch/csky/include/asm/cmpxchg.h
> +++ b/arch/csky/include/asm/cmpxchg.h
> @@ -6,6 +6,7 @@
>  #ifdef CONFIG_SMP
>  #include <linux/bug.h>
>  #include <asm/barrier.h>
> +#include <linux/cmpxchg-emu.h>
>
>  #define __xchg_relaxed(new, ptr, size)                         \
>  ({                                                             \
> @@ -61,6 +62,9 @@
>         __typeof__(old) __old = (old);                          \
>         __typeof__(*(ptr)) __ret;                               \
>         switch (size) {                                         \
> +       case 1:                                                 \
> +               __ret = (__typeof__(*(ptr)))cmpxchg_emu_u8((volatile u8 *)__ptr, (uintptr_t)__old, (uintptr_t)__new); \
> +               break;                                          \
>         case 4:                                                 \
>                 asm volatile (                                  \
>                 "1:     ldex.w          %0, (%3) \n"            \
> @@ -91,6 +95,9 @@
>         __typeof__(old) __old = (old);                          \
>         __typeof__(*(ptr)) __ret;                               \
>         switch (size) {                                         \
> +       case 1:                                                 \
> +               __ret = (__typeof__(*(ptr)))cmpxchg_emu_u8((volatile u8 *)__ptr, (uintptr_t)__old, (uintptr_t)__new); \
> +               break;                                          \
>         case 4:                                                 \
>                 asm volatile (                                  \
>                 "1:     ldex.w          %0, (%3) \n"            \
> @@ -122,6 +129,9 @@
>         __typeof__(old) __old = (old);                          \
>         __typeof__(*(ptr)) __ret;                               \
>         switch (size) {                                         \
> +       case 1:                                                 \
> +               __ret = (__typeof__(*(ptr)))cmpxchg_emu_u8((volatile u8 *)__ptr, (uintptr_t)__old, (uintptr_t)__new); \
> +               break;                                          \
>         case 4:                                                 \
>                 asm volatile (                                  \
>                 RELEASE_FENCE                                   \
> --
> 2.40.1
>
Reviewed-by: Guo Ren <guoren@...nel.org>

I will optimize it after ARCH_NEED_CMPXCHG_1_EMU is merged.

-- 
Best Regards
 Guo Ren