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

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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 :(


greg k-h

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