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

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Date: Sat, 11 May 2024 07:49:57 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Guo Ren <guoren@...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 Sat, May 11, 2024 at 02:42:17PM +0800, Guo Ren wrote:
> 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.

Thank you very much!  I have applied this and added it to my pull
request for the upcoming merge window.

							Thanx, Paul