Re: [PATCH v1 00/12] add FPGA hotplug manager driver

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On Thu, Jan 19, 2023 at 2:34 PM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
>
> On Wed, Jan 18, 2023 at 08:35:50PM -0500, Tianfei Zhang wrote:
> > This patchset introduces the FPGA hotplug manager (fpgahp) driver which
> > has been verified on the Intel N3000 card.
> >
> > When a PCIe-based FPGA card is reprogrammed, it temporarily disappears
> > from the PCIe bus. This needs to be managed to avoid PCIe errors and to
> > reprobe the device after reprogramming.
> >
> > To change the FPGA image, the kernel burns a new image into the flash on
> > the card, and then triggers the card BMC to load the new image into FPGA.
> > A new FPGA hotplug manager driver is introduced that leverages the PCIe
> > hotplug framework to trigger and manage the update of the FPGA image,
> > including the disappearance and reappearance of the card on the PCIe bus.
> > The fpgahp driver uses APIs from the pciehp driver. Two new operation
> > callbacks are defined in hotplug_slot_ops:
> >
> >   - available_images: Optional: available FPGA images
> >   - image_load: Optional: trigger the FPGA to load a new image
> >
> >
> > The process of reprogramming an FPGA card begins by removing all devices
> > associated with the card that are not required for the reprogramming of
> > the card. This includes PCIe devices (PFs and VFs) associated with the
> > card as well as any other types of devices (platform, etc.) defined within
> > the FPGA. The remaining devices are referred to here as "reserved" devices.
> > After triggering the update of the FPGA card, the reserved devices are also
> > removed.
> >
> > The complete process for reprogramming the FPGA are:
> >     1. remove all PFs and VFs except for PF0 (reserved).
> >     2. remove all non-reserved devices of PF0.
> >     3. trigger FPGA card to do the image update.
> >     4. disable the link of the hotplug bridge.
> >     5. remove all reserved devices under hotplug bridge.
> >     6. wait for image reload done via BMC, e.g. 10s.
> >     7. re-enable the link of hotplug bridge
> >     8. enumerate PCI devices below the hotplug bridge
> >
> > usage example:
> > [root@localhost]# cd /sys/bus/pci/slot/X-X/
> >
> > Get the available images.
> > [root@localhost 2-1]# cat available_images
> > bmc_factory bmc_user retimer_fw
> >
> > Load the request images for FPGA Card, for example load the BMC user image:
> > [root@localhost 2-1]# echo bmc_user > image_load
>
> Why is all of this tied into the pci hotplug code? Shouldn't it be
> specific to this one driver instead?  pci hotplug is for removing/adding
> PCI devices to the system, not messing with FPGA images.
>
> This feels like an abuse of the pci hotplug bus to me as this is NOT
> really a PCI hotplug bus at all, right?
>
> Or is it?  If so, then the slots should show up under the PCI device
> itself, not in /sys/bus/pci/slot/.  That location is there for old old
> stuff, we probably should move it one of these days as there's lots of
> special-cases in the driver core just because of that :(

I'm not sure if I can agree with this statement.

The slot here is what is registered via pci_hp_register(), isn't it?

There are multiple users of this in the tree, including ACPI-based PCI
hotplug, which is not really that old.

Are you saying that this should not be used?



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