[PATCH 02/10] powerpc/xive: guest exploitation of the XIVE interrupt controller

[Cédric Le Goater]

>>>> +static void xive_spapr_update_pending(struct xive_cpu *xc)
>>>> +{
>>>> +	u8 nsr, cppr;
>>>> +	u16 ack;
>>>> +
>>>> +	/* Perform the acknowledge hypervisor to register cycle */
>>>> +	ack = be16_to_cpu(__raw_readw(xive_tima + TM_SPC_ACK_OS_REG));
>>>
>>> Why do you need the raw_readw() + be16_to_cpu + mb, rather than one of
>>> the higher level IO helpers?
>>
>> This is one of the many ways to do MMIOs on the TIMA. This memory 
>> region defines a set of offsets and sizes for which loads and 
>> stores have different effects. 
>>
>> See the arch/powerpc/include/asm/xive-regs.h file and 
>> arch/powerpc/kvm/book3s_xive_template.c for some more usage.
> 
> Sure, much like any IO region.  My point is, why do you want this kind
> of complex combo, rather than say an in_be16() or readw_be().
> 

The code is inherited from the native backend. 

I think this is because we know what we are doing and we skip 
the synchronization routines of the higher level IO helpers. 
That might not be necessary for sPAPR. Ben ? 

Thanks,

C.