RE: [PATCH v2 05/12] iommu: Allow iommu driver to populate the max_pasids

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> From: Baolu Lu <baolu.lu@xxxxxxxxxxxxxxx>
> Sent: Monday, April 15, 2024 1:42 PM
> 
> On 4/12/24 4:15 PM, Yi Liu wrote:
> > Today, the iommu layer gets the max_pasids by pci_max_pasids() or
> reading
> > the "pasid-num-bits" property. This requires the non-PCI devices to have a
> > "pasid-num-bits" property. Like the mock device used in iommufd selftest,
> > otherwise the max_pasids check would fail in iommu layer.
> >
> > While there is an alternative, the iommu layer can allow the iommu driver
> > to set the max_pasids in its probe_device() callback and populate it. This
> > is simpler and has no impact on the existing cases.
> >
> > Suggested-by: Jason Gunthorpe<jgg@xxxxxxxxxx>
> > Signed-off-by: Yi Liu<yi.l.liu@xxxxxxxxx>
> > ---
> >   drivers/iommu/iommu.c | 9 +++++----
> >   1 file changed, 5 insertions(+), 4 deletions(-)
> 
> The code does not appear to match the commit message here.
> 
> The code in change is a refactoring by folding the max_pasid assignment
> into its helper. However, the commit message suggests a desire to expose
> some kind of kAPI for device drivers.
> 

it's not about exposing a new kAPI. Instead it allows the driver to
manually set dev->iommu->max_pasids before calling
iommu_init_device(). kind of another contract to convey the
max pasid.

But as how you are confused, I prefer to defining a "pasid-num-bits"
property in the mock driver. It's easier to understand.




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