Re: [PATCH 3/5] ARC: Emulate two-byte cmpxchg

[Vineet Gupta]

On 10/7/26 22:36, Paul E. McKenney wrote:
> From: Bradley Morgan <brads@xxxxxxxxxxxxxx>
>
> ARC has no two-byte atomic compare and swap, so the
> arch_cmpxchg_relaxed() macro switch lets 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 the dispatch keeps the (uintptr_t)
> casts the case 1 path already uses.
>
> The sizeof(*(_p_)) fix that v4 folded in here landed separately
> through Vineet's f050c3e61d2a, so this patch is now only the
> case 2 wiring.
>
> Signed-off-by: Bradley Morgan <brads@xxxxxxxxxxxxxx>
> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>

Acked-by: Vineet Gupta <vgupta@xxxxxxxxxx>

Thx,
-Vineet

> ---
>   arch/arc/include/asm/cmpxchg.h | 3 +++
>   1 file changed, 3 insertions(+)
>
> diff --git a/arch/arc/include/asm/cmpxchg.h b/arch/arc/include/asm/cmpxchg.h
> index 76f43db0890fc..7157718f147c1 100644
> --- a/arch/arc/include/asm/cmpxchg.h
> +++ b/arch/arc/include/asm/cmpxchg.h
> @@ -50,6 +50,9 @@
>   	case 1:								\
>   		_prev_ = (__typeof__(*(ptr)))cmpxchg_emu_u8((volatile u8 *__force)_p_, (uintptr_t)_o_, (uintptr_t)_n_);	\
>   		break;							\
> +	case 2:								\
> +		_prev_ = (__typeof__(*(ptr)))cmpxchg_emu_u16((volatile u16 *__force)_p_, (unsigned long)_o_, (unsigned long)_n_);	\
> +		break;							\
>   	case 4:								\
>   		_prev_ = __cmpxchg(_p_, _o_, _n_);			\
>   		break;							\