Re: [RFC PATCH v2 00/10] vfio/mdev: IOMMU aware mediated device

[Lu Baolu <baolu.lu@linux.intel.com>]

Hi,

On 09/13/2018 01:54 AM, Jean-Philippe Brucker wrote:
> On 12/09/2018 03:42, Lu Baolu wrote:
>> Hi,
>>
>> On 09/11/2018 12:22 AM, Jean-Philippe Brucker wrote:
>>> Hi,
>>>
>>> On 30/08/2018 05:09, Lu Baolu wrote:
>>>> Below APIs are introduced in the IOMMU glue for device drivers to use
>>>> the finer granularity translation.
>>>>
>>>> * iommu_capable(IOMMU_CAP_AUX_DOMAIN)
>>>>     - Represents the ability for supporting multiple domains per device
>>>>       (a.k.a. finer granularity translations) of the IOMMU hardware.
>>> iommu_capable() cannot represent hardware capabilities, we need
>>> something else for systems with multiple IOMMUs that have different
>>> caps. How about iommu_domain_get_attr on the device's domain instead?
>> Domain is not a good choice for per iommu cap query. A domain might be
>> attached to devices belonging to different iommu's.
>>
>> How about an API with device structure as parameter? A device always
>> belongs to a specific iommu. This API is supposed to be used the
>> device driver.
> Ah right, domain attributes won't work. Your suggestion seems more
> suitable, but maybe users can simply try to enable auxiliary domains
> first, and conclude that the IOMMU doesn't support it if it returns an error
> 

Some driver might want to check whether hardware supports AUX_DOMAIN
during the driver probe stage, but doesn't want to enable AUX_DOMAIN
at that time. One reasonable use case is driver check AUX_DOMAIN cap
during driver probe and expose different sysfs nodes according to
whether AUX_DOMAIN is support or not, then AUX_DOMAIN is enabled or 
disabled during run time through a sysfs node. With this consideration,
we still need a API to check cap.

How about

* iommu_check_aux_domain(struct device *dev)
    - Check whether the iommu driver supports multiple domains on @dev.

Best regards,
Lu Baolu