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

[Jason Gunthorpe <jgg@nvidia.com>]

On Sat, Apr 20, 2024 at 01:45:57PM +0800, Yi Liu wrote:
> On 2024/4/17 16:49, Tian, Kevin wrote:
> > > From: Baolu Lu <baolu.lu@linux.intel.com>
> > > 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@nvidia.com>
> > > > Signed-off-by: Yi Liu<yi.l.liu@intel.com>
> > > > ---
> > > >    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.
> 
> @Jason, how about your thought? :) Adding a "pasid-num-bits" may be
> more straightforward.

Sure, just make sure it doesn't leak memory...

Jason