linux-kernel - Re: [RFC][PATCH 06/31] locking,avr32: Implement atomic_fetch

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Date:	Fri, 22 Apr 2016 13:58:20 +0200
From:	Hans-Christian Noren Egtvedt <egtvedt@...fundet.no>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	torvalds@...ux-foundation.org, mingo@...nel.org,
	tglx@...utronix.de, will.deacon@....com,
	paulmck@...ux.vnet.ibm.com, boqun.feng@...il.com,
	waiman.long@....com, fweisbec@...il.com,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	rth@...ddle.net, vgupta@...opsys.com, linux@....linux.org.uk,
	realmz6@...il.com, ysato@...rs.sourceforge.jp, rkuo@...eaurora.org,
	tony.luck@...el.com, geert@...ux-m68k.org, james.hogan@...tec.com,
	ralf@...ux-mips.org, dhowells@...hat.com, jejb@...isc-linux.org,
	mpe@...erman.id.au, schwidefsky@...ibm.com, dalias@...c.org,
	davem@...emloft.net, cmetcalf@...lanox.com, jcmvbkbc@...il.com,
	arnd@...db.de, dbueso@...e.de, fengguang.wu@...el.com
Subject: Re: [RFC][PATCH 06/31] locking,avr32: Implement
 atomic_fetch_{add,sub,and,or,xor}()

Around Fri 22 Apr 2016 11:04:19 +0200 or thereabout, Peter Zijlstra wrote:
> Implement FETCH-OP atomic primitives, these are very similar to the
> existing OP-RETURN primitives we already have, except they return the
> value of the atomic variable _before_ modification.
> 
> This is especially useful for irreversible operations -- such as
> bitops (because it becomes impossible to reconstruct the state prior
> to modification).
> 
> 
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

Looks good.

Acked-by: Hans-Christian Noren Egtvedt <egtvedt@...fundet.no>

> ---
>  arch/avr32/include/asm/atomic.h |   56 ++++++++++++++++++++++++++++++++++++----
>  1 file changed, 51 insertions(+), 5 deletions(-)
> 
> --- a/arch/avr32/include/asm/atomic.h
> +++ b/arch/avr32/include/asm/atomic.h
> @@ -41,21 +41,51 @@ static inline int __atomic_##op##_return
>  	return result;							\
>  }
>  
> +#define ATOMIC_FETCH_OP(op, asm_op, asm_con)				\
> +static inline int __atomic_fetch_##op(int i, atomic_t *v)		\
> +{									\
> +	int result, val;						\
> +									\
> +	asm volatile(							\
> +		"/* atomic_fetch_" #op " */\n"				\
> +		"1:	ssrf	5\n"					\
> +		"	ld.w	%0, %3\n"				\
> +		"	mov	%1, %0\n"				\
> +		"	" #asm_op "	%1, %4\n"			\
> +		"	stcond	%2, %1\n"				\
> +		"	brne	1b"					\
> +		: "=&r" (result), "=&r" (val), "=o" (v->counter)	\
> +		: "m" (v->counter), #asm_con (i)			\
> +		: "cc");						\
> +									\
> +	return result;							\
> +}
> +
>  ATOMIC_OP_RETURN(sub, sub, rKs21)
>  ATOMIC_OP_RETURN(add, add, r)
> +ATOMIC_FETCH_OP (sub, sub, rKs21)
> +ATOMIC_FETCH_OP (add, add, r)
>  
> -#define ATOMIC_OP(op, asm_op)						\
> +#define atomic_fetch_or atomic_fetch_or
> +
> +#define ATOMIC_OPS(op, asm_op)						\
>  ATOMIC_OP_RETURN(op, asm_op, r)						\
>  static inline void atomic_##op(int i, atomic_t *v)			\
>  {									\
>  	(void)__atomic_##op##_return(i, v);				\
> +}									\
> +ATOMIC_FETCH_OP(op, asm_op, r)						\
> +static inline int atomic_fetch_##op(int i, atomic_t *v)		\
> +{									\
> +	return __atomic_fetch_##op(i, v);				\
>  }
>  
> -ATOMIC_OP(and, and)
> -ATOMIC_OP(or, or)
> -ATOMIC_OP(xor, eor)
> +ATOMIC_OPS(and, and)
> +ATOMIC_OPS(or, or)
> +ATOMIC_OPS(xor, eor)
>  
> -#undef ATOMIC_OP
> +#undef ATOMIC_OPS
> +#undef ATOMIC_FETCH_OP
>  #undef ATOMIC_OP_RETURN
>  
>  /*
> @@ -87,6 +117,14 @@ static inline int atomic_add_return(int
>  	return __atomic_add_return(i, v);
>  }
>  
> +static inline int atomic_fetch_add(int i, atomic_t *v)
> +{
> +	if (IS_21BIT_CONST(i))
> +		return __atomic_fetch_sub(-i, v);
> +
> +	return __atomic_fetch_add(i, v);
> +}
> +
>  /*
>   * atomic_sub_return - subtract the atomic variable
>   * @i: integer value to subtract
> @@ -102,6 +140,14 @@ static inline int atomic_sub_return(int
>  	return __atomic_add_return(-i, v);
>  }
>  
> +static inline int atomic_fetch_sub(int i, atomic_t *v)
> +{
> +	if (IS_21BIT_CONST(i))
> +		return __atomic_fetch_sub(i, v);
> +
> +	return __atomic_fetch_add(-i, v);
> +}
> +
>  /*
>   * __atomic_add_unless - add unless the number is a given value
>   * @v: pointer of type atomic_t
-- 
mvh
Hans-Christian Noren Egtvedt