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

[Guo Ren]

On Thu, Oct 8, 2026 at 4:36 AM Paul E. McKenney <paulmck@xxxxxxxxxx> wrote:
>
> From: Bradley Morgan <brads@xxxxxxxxxxxxxx>
>
> 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@xxxxxxxxxxxxxx>
> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
> ---
>  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@xxxxxxxxxx>

>                 break;                                          \
>         case 4:                                                 \
>                 asm volatile (                                  \
> --
> 2.40.1
>


-- 
Best Regards
 Guo Ren