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ARC: Emulate two-byte cmpxchg

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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 f050c3e61d, so this patch is now only the
case 2 wiring.

Signed-off-by: Bradley Morgan <brads@mainlining.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Acked-by: Vineet Gupta <vgupta@kernel.org>
This commit is contained in:
Bradley Morgan 2026-10-05 12:06:58 +00:00 committed by Paul E. McKenney
parent 887685c52e
commit c1703c8772
1 changed files with 3 additions and 0 deletions
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3
arch/arc/include/asm/cmpxchg.h
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@ -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; \