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

[Julien Grall <julien@xxxxxxx>]

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