On Fri, Jan 20, 2023 at 08:28:51AM -0800, Russ Weight wrote: > On 1/19/23 05:33, Greg KH 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 > > > > 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? > > While it is true that triggering an FPGA image-load does not involve > hotplug specific registers to be managed, the RTL that comprises > the PCIe interface will disappear and then reappear after the FPGA > is reprogrammed. When it reappears, it_could/_/have a different PCI > ID. The process of managing this event has a lot of similarity to a > PCIe hotplug event; there is a lot of existing PCIe hotplug related > code that could be leveraged. It sounds like the N3000 is a PCI endpoint device which, when reprogrammed, briefly disappears from the bus and then may reappear under a different device ID. What you want to do then is make sure that the slot into which the N3000 is plugged is hotplug-capable. In that case, pciehp will handle disappearance and reappearance of the card just fine. Once the N3000 disables the link, pciehp will bring down the slot. Once it re-enables the link, it will bring the slot up again. It's as if the card was removed and replaced with a different one. pciehp will bind to the Root Port or Downstream Port associated with the hotplug slot. The pci_hotplug_port infrastructure is for hotplug controllers which handle devices disappearing and reappearing *below* them. It is not for endpoint devices. Thanks, Lukas
