Re: [PATCH v1 02/14] xen/pci: solve compilation error on ARM with HAS_PCI enabled

[Julien Grall <julien@xen.org>]

Hi Rahul,

On 20/08/2021 11:30, Rahul Singh wrote:
>> Please add a comment explaining why this just returns 0.
> 
> Here is the comment that I will add in next version.
> /*
>   * Return 0 as on ARM there is no pci physical irqs that required cleanup.
>   */

In this context, PIRQ means an interrupts that was routed to the guest 
and could be mapped to an event channel. We have no such concept on Arm 
(see allocate_pirq_struct()).

So I would write "PIRQ event channels are not supported on Arm, so 
nothing to do".

> 
>>
>>> +
>>> +/*
>>> + * Local variables:
>>> + * mode: C
>>> + * c-file-style: "BSD"
>>> + * c-basic-offset: 4
>>> + * tab-width: 4
>>> + * indent-tabs-mode: nil
>>> + * End:
>>> + */
>>> diff --git a/xen/drivers/passthrough/arm/iommu.c b/xen/drivers/passthrough/arm/iommu.c
>>> index db3b07a571..fdec1c5547 100644
>>> --- a/xen/drivers/passthrough/arm/iommu.c
>>> +++ b/xen/drivers/passthrough/arm/iommu.c
>>> @@ -135,3 +135,8 @@ void arch_iommu_domain_destroy(struct domain *d)
>>>   void __hwdom_init arch_iommu_hwdom_init(struct domain *d)
>>>   {
>>>   }
>>> +
>>> +bool arch_iommu_use_permitted(const struct domain *d)
>>> +{
>>> +    return true;
>>> +}
>>
>> Please add a comment explaining why returning true is always fine.
> 
> Here is the comment that I will add in next version:
> 
> /*
>   * Return true as iommu use is always permitted if mem-sharing,
>   * mem-paging, or log-dirty functionality is not enabled.
>   */
How about writing "Unlike x86, Arm doesn't support mem-sharing, 
mem-paging and log-dirty (yet). So there is no restriction to use the 
IOMMU".

This would make clear why you are mentioning mem-sharing, mem-paging & co.

Cheers,

-- 
Julien Grall