linux-kernel - Re: [PATCH] local_t : powerpc extension

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Message-Id: <3D84FDC0-3AA0-4144-A255-19D2E20AF0AA@kernel.crashing.org>
Date:	Thu, 15 Feb 2007 15:29:59 -0600
From:	Kumar Gala <galak@...nel.crashing.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] local_t : powerpc extension - use long for powerpc32


On Feb 15, 2007, at 3:23 PM, Mathieu Desnoyers wrote:

> * Kumar Gala (galak@...nel.crashing.org) wrote:
>>
>> On Feb 15, 2007, at 2:02 PM, Mathieu Desnoyers wrote:
>>
>>> * Kumar Gala (galak@...nel.crashing.org) wrote:
>>>> is there a reason this isn't local_add_return(long a, local_t  
>>>> *l) on
>>>> ppc32?
>>>>
>>>> (same comment for other functions)
>>>>
>>>> - k
>>>
>>> no, except that we use the code is taken from atomic.h and used an
>>> int parameter. However, due to the semantics of local_t, we should
>>> manipulate longs instead of ints, even if they are the same size  
>>> on a
>>> given architecture (ppc32 and mips32 are affectec by this).
>>>
>>> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
>>
>> Right, this means we can simply for ppc version down to:
>>
>> +static __inline__ int local_add_return(int a, local_t *l)
>> +{
>> +	int t;
>> +
>> +	__asm__ __volatile__(
>> +"1:	PPC_LLARX	%0,0,%2		# local_add_return\n\
>> +	add	%0,%1,%0\n"
>> +	PPC405_ERR77(0,%2)
>> +"	PPC_STLCX	%0,0,%2 \n\
> what about the dot after stwcx ? (stwcx.) ? Is it no longer required ?

Its implied, PPC_LLARX and PPC_STLCW are #defines that expand to  
proper instructions.

(look in include/asm-powerpc/asm-compat.h) for the defines.

Also, the PPC405_ERR77 will preprocess out on ppc64 if you were  
concerned.

- k
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