On Thu, Jan 19, 2023 at 02:43:21PM +0100, Rafael J. Wysocki wrote: > 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? Yes, but is it really a "slot" like a normal PCI slot? > There are multiple users of this in the tree, including ACPI-based PCI > hotplug, which is not really that old. It's really old, I think I worked on that in the 2.4/2.5 days? Anyway, it's been around a long time. > Are you saying that this should not be used? I'm saying that PCI is the only subsystem/bus that has something like this and we have a number of functions exported in the driver core only for the pci hotplug slot list. Which kind of implies that maybe it should be moved to something else? I don't have any specific ideas what it should be, just that it feels really odd as-is still. thanks, greg k-h
