Re: [Xen-devel] [PATCH v3 13/13] xen/iommu: smmu: Advertise when the SMMU support coherent table walk

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Fri, 2015-02-20 at 14:15 +0000, Julien Grall wrote:
> On 20/02/15 14:13, Ian Campbell wrote:
> > On Fri, 2015-02-20 at 14:07 +0000, Julien Grall wrote:
> >> On 20/02/15 13:34, Ian Campbell wrote:
> >>> On Fri, 2015-01-30 at 18:49 +0000, Julien Grall wrote:
> >>>> @@ -2896,6 +2911,16 @@ static __init int arm_smmu_dt_init(struct 
> >>>> dt_device_node *dev,
> >>>>          if ( !rc )
> >>>>                  iommu_set_ops(&arm_smmu_iommu_ops);
> >>>>  
> >>>> +        /*
> >>>> +         * The last added SMMU is the first element of arm_smmu_devices.
> >>>> +         * It's not necessary to take the lock because only the boot 
> >>>> CPU is
> >>>> +         * initialized the SMMU devices.
> >>>
> >>> Why is only the last added SMMU of interest? Do we not need to take the
> >>> union and/or intersection of them all?
> >>
> >> It's already the case. The function arm_smmu_dt_init is called on every
> >> SMMU. So the last added SMMU is the one we are currently added.
> > 
> > Why do we not just have it in our hand and have to go scrobbling round
> > in a list then?
> 
> [..]
> 
> > Rather than making assumptions about the list ordering and if we can't
> > just get hold of the smmu pointer directly from arm_smmu_dt_init then
> > I'd prefer an explicit walk of the list at some appropriate point after
> > everything has been registered up.
> 
> Because that would require to modify more heavily arm_smmu_dt_init.
> 
> Given that we control the way we add the SMMU in the list,

In a different bit of code on the other side of an ABI.

>  the explicit
> walk sounds pointless.
> 
> Regards,
> 



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