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

["Tian, Kevin" <kevin.tian@intel.com>]

> From: Lu Baolu [mailto:baolu.lu@linux.intel.com]
> Sent: Friday, September 14, 2018 10:47 AM
> 
> 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.
> 

maybe generalized as iommu_check_attr with aux_domain as a flag,
in case other IOMMU checks introduced in the future. hinted by Jean's
comment on iommu_sva_device_init part.

Thanks
Kevin