Re: [PATCH 4/5] csky: Emulate two-byte cmpxchg

["Paul E. McKenney" <paulmck@kernel.org>]

On Thu, Oct 08, 2026 at 01:54:57PM +0800, Guo Ren wrote:
> On Thu, Oct 8, 2026 at 4:36 AM Paul E. McKenney <paulmck@kernel.org> wrote:
> >
> > From: Bradley Morgan <brads@mainlining.org>
> >
> > C-SKY has no two-byte atomic compare and swap, so the __cmpxchg()
> > macros let case 2 fall through to BUILD_BUG() via default, and a
> > two-byte cmpxchg() fails the build.
> >
> > Route case 2 through the new cmpxchg_emu_u16(), which narrows the
> > old and new values itself, so all three orderings, relaxed, acquire
> > and full, keep the (uintptr_t) casts the case 1 path already uses.
> >
> > Signed-off-by: Bradley Morgan <brads@mainlining.org>
> > Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> > ---
> >  arch/csky/include/asm/cmpxchg.h | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> >
> > diff --git a/arch/csky/include/asm/cmpxchg.h b/arch/csky/include/asm/cmpxchg.h
> > index db6dda47184e4..6f3ca79e54acf 100644
> > --- a/arch/csky/include/asm/cmpxchg.h
> > +++ b/arch/csky/include/asm/cmpxchg.h
> > @@ -64,6 +64,9 @@
> >         switch (size) {                                         \
> >         case 1:                                                 \
> >                 __ret = (__typeof__(*(ptr)))cmpxchg_emu_u8((volatile u8 *)__ptr, (uintptr_t)__old, (uintptr_t)__new); \
> > +               break;                                                  \
> > +       case 2:                                                 \
> > +               __ret = (__typeof__(*(ptr)))cmpxchg_emu_u16((volatile u16 *)__ptr, (unsigned long)__old, (unsigned long)__new); \
> >                 break;                                          \
> >         case 4:                                                 \
> >                 asm volatile (                                  \
> > @@ -97,6 +100,9 @@
> >         switch (size) {                                         \
> >         case 1:                                                 \
> >                 __ret = (__typeof__(*(ptr)))cmpxchg_emu_u8((volatile u8 *)__ptr, (uintptr_t)__old, (uintptr_t)__new); \
> > +               break;                                                  \
> > +       case 2:                                                 \
> > +               __ret = (__typeof__(*(ptr)))cmpxchg_emu_u16((volatile u16 *)__ptr, (unsigned long)__old, (unsigned long)__new); \
> >                 break;                                          \
> >         case 4:                                                 \
> >                 asm volatile (                                  \
> > @@ -131,6 +137,9 @@
> >         switch (size) {                                         \
> >         case 1:                                                 \
> >                 __ret = (__typeof__(*(ptr)))cmpxchg_emu_u8((volatile u8 *)__ptr, (uintptr_t)__old, (uintptr_t)__new); \
> > +               break;                                                  \
> > +       case 2:                                                 \
> > +               __ret = (__typeof__(*(ptr)))cmpxchg_emu_u16((volatile u16 *)__ptr, (unsigned long)__old, (unsigned long)__new); \
> LGTM!
> 
> Acked-by: GUO Ren <guoren@kernel.org>

Thank you!  I will apply this on my next rebase.

							Thanx, Paul

> >                 break;                                          \
> >         case 4:                                                 \
> >                 asm volatile (                                  \
> > --
> > 2.40.1
> >
> 
> 
> -- 
> Best Regards
>  Guo Ren