RE: [RFC] /dev/ioasid uAPI proposal

[Tian, Kevin]

Hi, Jason,

> From: Jason Gunthorpe
> Sent: Thursday, June 3, 2021 9:05 PM
> 
> On Thu, Jun 03, 2021 at 06:39:30AM +0000, Tian, Kevin wrote:
> > > > Two helper functions are provided to support VFIO_ATTACH_IOASID:
> > > >
> > > > 	struct attach_info {
> > > > 		u32	ioasid;
> > > > 		// If valid, the PASID to be used physically
> > > > 		u32	pasid;
> > > > 	};
> > > > 	int ioasid_device_attach(struct ioasid_dev *dev,
> > > > 		struct attach_info info);
> > > > 	int ioasid_device_detach(struct ioasid_dev *dev, u32 ioasid);
> > >
> > > Honestly, I still prefer this to be highly explicit as this is where
> > > all device driver authors get invovled:
> > >
> > > ioasid_pci_device_attach(struct pci_device *pdev, struct ioasid_dev *dev,
> > > u32 ioasid);
> > > ioasid_pci_device_pasid_attach(struct pci_device *pdev, u32
> *physical_pasid,
> > > struct ioasid_dev *dev, u32 ioasid);
> >
> > Then better naming it as pci_device_attach_ioasid since the 1st parameter
> > is struct pci_device?
> 
> No, the leading tag indicates the API's primary subystem, in this case
> it is iommu (and if you prefer list the iommu related arguments first)
> 

I have a question on this suggestion when working on v2.

Within IOMMU fd it uses only the generic struct device pointer, which
is already saved in struct ioasid_dev at device bind time:

	struct ioasid_dev *ioasid_register_device(struct ioasid_ctx *ctx,
		struct device *device, u64 device_label);

What does this additional struct pci_device bring when it's specified in
the attach call? If we save it in attach_data, at which point will it be
used or checked? 

Can you help elaborate?

Thanks
Kevin