RE: [RFC 09/20] iommu: Add page size and address width attributes

[Tian, Kevin]

> From: Eric Auger <eric.auger@xxxxxxxxxx>
> Sent: Wednesday, September 22, 2021 9:43 PM
> 
> Hi,
> 
> On 9/19/21 8:38 AM, Liu Yi L wrote:
> > From: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> >
> > This exposes PAGE_SIZE and ADDR_WIDTH attributes. The iommufd could
> use
> > them to define the IOAS.
> >
> > Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> > ---
> >  include/linux/iommu.h | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> > index 943de6897f56..86d34e4ce05e 100644
> > --- a/include/linux/iommu.h
> > +++ b/include/linux/iommu.h
> > @@ -153,9 +153,13 @@ enum iommu_dev_features {
> >  /**
> >   * enum iommu_devattr - Per device IOMMU attributes
> >   * @IOMMU_DEV_INFO_FORCE_SNOOP [bool]: IOMMU can force DMA to
> be snooped.
> > + * @IOMMU_DEV_INFO_PAGE_SIZE [u64]: Page sizes that iommu
> supports.
> > + * @IOMMU_DEV_INFO_ADDR_WIDTH [u32]: Address width supported.
> I think this deserves additional info. What address width do we talk
> about, input, output, what stage if the IOMMU does support multiple stages
> 

it describes the address space width, thus is about input.

when multiple stages are supported, each stage is represented by a separate
ioasid, each with its own addr_width