Re: [PATCH V2 1/4] drivers/fpga/amd: Add new driver amd versal-pci

[Yidong Zhang]

On 2/6/25 20:40, Xu Yilun wrote:
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>
> On Thu, Feb 06, 2025 at 07:16:25PM -0800, Yidong Zhang wrote:
> > On 2/6/25 18:19, Xu Yilun wrote:
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> > >
> > >
> > > > > No need to detach a specific driver, remove all devices in the
> > > > > fpga-region. I imagine this could also be a generic flow for all PCI/e
> > > > > based FPGA cards.
> > > >
> > > > I see your point. Is there an existing example in current fpga driver for
> > > > PCI/e based cards?
> > >
> > > No. The fpga-region re-enumeration arch is still WIP, so no existing
> > > implementation.
> >
> > Got you. I can also help to test or provide feedback.
> > Actually, I had sent Nava my protype of using configfs for the non-OF
> > driver. He should have the updated patch soon.
> >
> > > > We will need to talk to our management team and re-design our driver.
> > > > I think we have 2 approaches:
> > > > 1) Align with linux fpga, having one driver for both userPF and mgmtPF; or
> > >
> > > Don't get you. Linux FPGA doesn't require one driver for both PFs.
> >
> > I assume when you said "generic flow for removing all devices in
> > fpga-region" means that there is a single driver which use the fpga-region
> > callbacks to remove all devices and then re-progream the FPGA.
> >
> > On AMD V70 hardware, the userPF has different deviceid than the mgmtPF.
> > Thus, our current design is having 2 separate pcie drivers for each
> > different deviceid.
> >
> > Thus, in our current design, the fpga-region should be in the userPF driver
> > which has callbacks to remove all devices. But in mgmtPF, it is more like a
>
> A question, if the FPGA logic is cleared, does the userPF still exist on
> PCIe bus?

I am not sure I fully understand your question by "FPGA logic is 
cleared". Based on our design, the userPF exists, but all services need 
to be re-configured after hardware is changed.


> > utility which only handles request from the userPF but it has the management
> > privilege. Usually, cloud vendors require the mgmtPF deployed in their
> > secured domain (can be a separate physical machine).
>
> I though mgmtPF & userPF are just 2 functions on one PCIe card, they are not?
> Then how the mgmtPF writes data to another physical machine and
> influence the userPF?

They are functions but they also have different device id thus we can 
bind different driver onto each of them.

I think I should interrupt it accurately as Host and VM. See details 
here please:
https://xilinx.github.io/XRT/2019.2/html/cloud_vendor_support.html

But, my point is that we do have 2 separate drivers.

Please let me know if you need more detailed info.

/David

> Thanks,
> Yilun
>
> > We can keep 2 drivers, one for userPF, one for mgmtPF. The userPF and mgmtPF
> > communicate each other via the communication channel because they can be
> > physically on different machine.
> >
> > Are you looking for us to upstream both of them together?
> > If yes, I still think that the fpga-region should be in the userPF driver.
> > The mgmtPF driver is still a utility driver.
> >
> > Please correct me if I am wrong.:)
> >
> > > > 2) find a different location (maybe driver/misc) for the version-pci driver,
> > > > because it is an utility driver, not need to be tied with fpga framework.
> > >
> > > I'm not the misc maintainer, but I assume in-tree utility driver +
> > > out-of-tree client driver is not generally welcomed.
> >
> > Great info! Thanks! I will have to discuss this with my team too.
> >
> > My understanding, so far based on your comments above, the drivers/fpga
> > prefer to use fpga-region ops to handle FPGA re-program changes.
> >
> > The current versal-pci driver is a utility driver.
> > The fpga-region should be within the userPF driver.
> >
> > We can try to make our userPF driver in-tree as well. But the current plan
> > is to do it later.
> >
> > If you prefer we do both of them together. I can talk to my team.
> >
> > Thanks,
> > David
> > > Thanks,
> > > Yilun
> > >
> > > > Please let me know you thoughts. Which way is acceptable by you.
> > > >
> > > > Thanks,
> > > > David
> > > > > Thanks,
> > > > > Yilun
> > > > >
> > > > > > driver and allow the userPF driver re-enumerate all to match the new
> > > > > > hardware.
> > > > > >
> > > > > > I think my understanding is correct, it is doable.
> > > > > >
> > > > > > As long as we can keep our userPF driver as separate driver, the code change
> > > > > > won't be too big.
> > > > > >
> > > > > > > Thanks,
> > > > > > > Yilun