Re: [Xen-devel] [PATCH v5 12/14] xen/arm: p2m: Clean cache PT when the IOMMU doesn't support coherent walk

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 14.05.14 at 11:09, <julien.grall@xxxxxxxxxx> wrote:
>>> @@ -139,6 +147,7 @@ struct iommu_ops {
>>>       void (*iotlb_flush)(struct domain *d, unsigned long gfn, unsigned int 
>>> page_count);
>>>       void (*iotlb_flush_all)(struct domain *d);
>>>       void (*dump_p2m_table)(struct domain *d);
>>> +    uint32_t (*features)(struct domain *d);
>>
>> I think I said this on an earlier round already - for future extensibility
>> this should return "const unsigned long *", and get accessed by the
>> wrapper function using test_bit(). Or even better without an accessor
>> function at all, just directly having a "const unsigned long *" field here.
>> Unless of course the backend implementation - which isn't part of this
>> patch - would have difficulty setting up a suitable bitfield during (early)
>> initialization.
> 
> The SMMU drivers handle multiple SMMUs. Each SMMU can have different 
> specifications (e.g coherent walk support or not).
> 
> As each domain doesn't use all SMMUs, we might be able to avoid flushing 
> PT on some of them. That's why I've choose to use a callback with the 
> domain in parameter.
> 
> I don't like the solution which return "unsigned long *" because we are 
> assuming the driver will always a valid pointer (for instance with 2 
> unsigned long), even if he doesn't need it.

In that case simply make this a bitmap embedded in struct iommu_ops,
which the driver has to populate suitably early. That way the individual
drivers don't need to care about the eventually growing size.

Jan


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