Re: [Xen-devel] [PATCH v6 10/31] xen/arm: ITS: Introduce gic_is_lpi helper function

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 01/09/15 10:02, Vijay Kilari wrote:
> On Mon, Aug 31, 2015 at 10:19 PM, Julien Grall <julien.grall@xxxxxxxxxx> 
> wrote:
>> Hi Vijay,
>>
>> On 31/08/2015 12:06, vijay.kilari@xxxxxxxxx wrote:
>>>
>>> diff --git a/xen/arch/arm/gic.c b/xen/arch/arm/gic.c
>>> index 758678d..2199963 100644
>>> --- a/xen/arch/arm/gic.c
>>> +++ b/xen/arch/arm/gic.c
>>> @@ -62,6 +62,15 @@ enum gic_version gic_hw_version(void)
>>>      return gic_hw_ops->info->hw_version;
>>>   }
>>>
>>> +#ifdef HAS_GICV3
>>> +bool_t gic_is_lpi(unsigned int irq)
>>> +{
>>> +    return (irq >= FIRST_GIC_LPI && irq < (1 <<
>>> gic_hw_ops->info->nr_id_bits));
>>
>>
>> It would make more sense to calculate the number of ID supported at boot
>> time rather than re-calculate everytime this function is called (i.e very
>> often).
>>
>>> +}
>>> +#else
>>> +bool_t gic_is_lpi(unsigned int irq) { return 0; }
>>> +#endif
>>
>>
>> I though I'd already say it on a previous version. I would like to avoid
>> seen any #ifdef HAS_GICV3 in the generic code include interrupt framework.
>>
>> In this case, I don't see much the benefit to do a specific case for
>> platform not using GICv3 (i.e ARM32).
> 
> You mean, let gic_is_lpi() implemented for both ARM64/32 and let this
> function fail
> always for ARM32?

Yes. You already implement it as always fail but with #ifdef. Although I
don't think this is worth to do as it's more difficult to maintain.

> Other option is to implement callback to hw drivers (gicv3 and gicv2).
> But overhead of callback
> should also be considered

It was the implementation you suggested on v5. And I wasn't not in favor
about it.

BTW, I suggested to create a field nr_lpis but you decided to store the
number of bits supported. Why?

Regards,

-- 
Julien Grall

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