Re: [PATCH] powerpc: Fix __cmpxchg() to take a volatile ptr again

[Pan Xinhui <xinhui@linux.vnet.ibm.com>]

在 2016/11/25 11:07, Michael Ellerman 写道:
> In commit d0563a1297e2 ("powerpc: Implement {cmp}xchg for u8 and u16")
> we removed the volatile from __cmpxchg().
>
> This is leading to warnings such as:
>
>   drivers/gpu/drm/drm_lock.c: In function ‘drm_lock_take’:
>   arch/powerpc/include/asm/cmpxchg.h:484:37: warning: passing argument 1
>   of ‘__cmpxchg’ discards ‘volatile’ qualifier from pointer target
>      (__typeof__(*(ptr))) __cmpxchg((ptr), (unsigned long)_o_,   \
>
> There doesn't seem to be consensus across architectures whether the
> argument is volatile or not, so at least for now put the volatile back.
>
> Fixes: d0563a1297e2 ("powerpc: Implement {cmp}xchg for u8 and u16")
> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
> ---
Hi, mpe
	We implement __cmpxchg in asm so volatile maybe is not needed I think.
But seems compiler is not happy :(
I am okay with your patch. thanks!

>  arch/powerpc/include/asm/cmpxchg.h | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/cmpxchg.h b/arch/powerpc/include/asm/cmpxchg.h
> index c12f110261b2..fc46b664c49e 100644
> --- a/arch/powerpc/include/asm/cmpxchg.h
> +++ b/arch/powerpc/include/asm/cmpxchg.h
> @@ -14,7 +14,7 @@
>  #endif
>
>  #define XCHG_GEN(type, sfx, cl)				\
> -static inline u32 __xchg_##type##sfx(void *p, u32 val)		\
> +static inline u32 __xchg_##type##sfx(volatile void *p, u32 val)	\
>  {								\
>  	unsigned int prev, prev_mask, tmp, bitoff, off;		\
>  								\
> @@ -40,7 +40,7 @@ static inline u32 __xchg_##type##sfx(void *p, u32 val)		\
>
>  #define CMPXCHG_GEN(type, sfx, br, br2, cl)			\
>  static inline							\
> -u32 __cmpxchg_##type##sfx(void *p, u32 old, u32 new)		\
> +u32 __cmpxchg_##type##sfx(volatile void *p, u32 old, u32 new)	\
>  {								\
>  	unsigned int prev, prev_mask, tmp, bitoff, off;		\
>  								\
> @@ -399,7 +399,7 @@ __cmpxchg_u64_acquire(u64 *p, unsigned long old, unsigned long new)
>  #endif
>
>  static __always_inline unsigned long
> -__cmpxchg(void *ptr, unsigned long old, unsigned long new,
> +__cmpxchg(volatile void *ptr, unsigned long old, unsigned long new,
>  	  unsigned int size)
>  {
>  	switch (size) {
>