[PATCH 04/13] powerpc: Use soft_enabled_set api to update paca->soft_enabled

[Madhavan Srinivasan]

On Friday 16 September 2016 05:13 PM, David Laight wrote:
> From: Nicholas Piggin
>> Sent: 16 September 2016 10:53
>> On Thu, 15 Sep 2016 18:31:54 +0530
>> Madhavan Srinivasan <maddy at linux.vnet.ibm.com> wrote:
>>
>>> Force use of soft_enabled_set() wrapper to update paca-soft_enabled
>>> wherever possisble. Also add a new wrapper function, soft_enabled_set_return(),
>>> added to force the paca->soft_enabled updates.
> ...
>>> diff --git a/arch/powerpc/include/asm/hw_irq.h b/arch/powerpc/include/asm/hw_irq.h
>>> index 8fad8c24760b..f828b8f8df02 100644
>>> --- a/arch/powerpc/include/asm/hw_irq.h
>>> +++ b/arch/powerpc/include/asm/hw_irq.h
>>> @@ -53,6 +53,20 @@ static inline notrace void soft_enabled_set(unsigned long enable)
>>>   	: : "r" (enable), "i" (offsetof(struct paca_struct, soft_enabled)));
>>>   }
>>>
>>> +static inline notrace unsigned long soft_enabled_set_return(unsigned long enable)
>>> +{
>>> +	unsigned long flags;
>>> +
>>> +	asm volatile(
>>> +		"lbz %0,%1(13); stb %2,%1(13)"
>>> +		: "=r" (flags)
>>> +		: "i" (offsetof(struct paca_struct, soft_enabled)),\
>>> +		  "r" (enable)
>>> +		: "memory");
>>> +
>>> +	return flags;
>>> +}
>> Why do you have the "memory" clobber here while soft_enabled_set() does not?
> I wondered about the missing memory clobber earlier.
>
> Any 'clobber' ought to be restricted to the referenced memory area.
> If the structure is only referenced by r13 through 'asm volatile' it isn't needed.
> OTOH why not allocate a global register variable to r13 and access through that?

I do see this in asm/paca.h "register struct paca_struct *local_paca 
asm("r13"); "
and __check_irq_replay() in kernel/irq.c do updates the "irq_happened" as
mentioned. But existing helpers in hw_irq update the soft_enabled via
asm volatile and i did the same.

Maddy

> 	David
>