Re: [PATCH v3] event/dlb2: fix disable PASID for kernel 6.2

[Jerin Jacob <jerinjacobk@gmail.com>]

On Tue, Oct 31, 2023 at 10:45 PM Bruce Richardson
<bruce.richardson@intel.com> wrote:
>
> On Tue, Oct 31, 2023 at 10:36:04PM +0530, Jerin Jacob wrote:
> > On Tue, Oct 31, 2023 at 8:43 PM Sevincer, Abdullah
> > <abdullah.sevincer@intel.com> wrote:
> > >
> > >
> > > > +This patch can be splited as two,
> > > > +1) Generic PCIe function to enable/disable PASID
> > > > +2) Call generic function to disable PASID in drivers/event/dlb2/. Also mention which Linux kernel commit is introducing this issue in the git commit log.
> > >
> > > Hi Jerrin,
> > > I think I need to provide more information here, then we can decide which way we will go would be good for now. I agree to having 2 functions in pci common
> > > code to enable/disable PASID, but we need to have hardcoded PASID cap offset inside these functions as well since PASID capability is not exposed to user. Hence, to be more specific
> > > main reason to have hardcoded PASID is, rte_pci_find_ext_capability() function to retrieve the offset returns '0' since PASID is not exposed to user yet.
> > >
> > > We can see this is vfio_pci_config.c in kernel code where PASID is not exposed to user.
> > > [PCI_EXT_CAP_ID_PASID]  =       0,      /* not yet */
> > >
> > > So if it is okay to go with hardcoded offset now in these functions I will move the implementation to pci_common file.
> >
> > I would suggest, add argument option to API whether to probe the
> > capability or not? - 0 means probe and- non zero means specific PASID
> > cap offset till Linux VFIO is exposing it.
>
> That doesn't seem particularly useful to me. The calling-API in the DPDK
> PMD (assuming it's PMD who use this), is no more likely to know whether
> probing will work. Therefore, I think we just hard-code the offset for now.

I think, there are three things here
1) Whether to have common API for dealing with generic function like
enabling PASID or not? - I think, we are in agreement to have common
public function(Implementation could be hard-coded or probe)
2) Since it is public PCIe API, I thought of adding probing in API as
it is just LINUX limitation now. No strong opinion on inclusion of
probe in on this as Linux is main EAL which supports PCIe now.
3) Since it is PCIe capability, In my understanding the offset will
change based on the number of capabilities available in PCIe config
space for a given device. _if so_, an additional argument for the
offset
needs to be passed from PMD to common PCI API(I.e it can not be
hard-coded in common PCI code)

> We can decide what the best approach is later on once kernel actually
> exposes the value to users. Only then will we know if it's possible to
> detect that exposure or not.
>
> /Bruce