On Mon, Aug 29, 2022 at 02:43:35PM -0700, Lizhi Hou wrote: > This patch series introduces OF overlay support for PCI devices which > primarily addresses two use cases. First, it provides a data driven method > to describe hardware peripherals that are present in a PCI endpoint and > hence can be accessed by the PCI host. An example device is Xilinx/AMD > Alveo PCIe accelerators. Second, it allows reuse of a OF compatible > driver -- often used in SoC platforms -- in a PCI host based system. An > example device is Microchip LAN9662 Ethernet Controller. > > This patch series consolidates previous efforts to define such an > infrastructure: > https://lore.kernel.org/lkml/20220305052304.726050-1-lizhi.hou@xxxxxxxxxx/ > https://lore.kernel.org/lkml/20220427094502.456111-1-clement.leger@xxxxxxxxxxx/ > > Normally, the PCI core discovers PCI devices and their BARs using the > PCI enumeration process. However, the process does not provide a way to > discover the hardware peripherals that are present in a PCI device, and > which can be accessed through the PCI BARs. Also, the enumeration process > does not provide a way to associate MSI-X vectors of a PCI device with the > hardware peripherals that are present in the device. PCI device drivers > often use header files to describe the hardware peripherals and their > resources as there is no standard data driven way to do so. This patch > series proposes to use flattened device tree blob to describe the > peripherals in a data driven way. Based on previous discussion, using > device tree overlay is the best way to unflatten the blob and populate > platform devices. To use device tree overlay, there are three obvious > problems that need to be resolved. Hi Lizhi, We all *love* "have you thought about xxx" questions but I would really like to get your thoughts on this. An approach to this problem that I have seen in various devices is to emulate a virtual pcie switch, and expose the "sub devices" behind that. That way you can carve up the BAR space, each device has its own config space and mapping of MSI-X vector to device becomes clear. This approach also integrates well with other kernel infrastructure (IOMMU, hotplug). This is certainly possible on reprogrammable devices but requires some more FPGA resources - though I don't believe the added utilization would be significant. What do you think of this kind of solution? Jeremi > > First, we need to create a base tree for non-DT system such as x86_64. A > patch series has been submitted for this: > https://lore.kernel.org/lkml/20220624034327.2542112-1-frowand.list@xxxxxxxxx/ > https://lore.kernel.org/lkml/20220216050056.311496-1-lizhi.hou@xxxxxxxxxx/ > > Second, a device tree node corresponding to the PCI endpoint is required > for overlaying the flattened device tree blob for that PCI endpoint. > Because PCI is a self-discoverable bus, a device tree node is usually not > created for PCI devices. This series adds support to generate a device > tree node for a PCI device which advertises itself using PCI quirks > infrastructure. > > Third, we need to generate device tree nodes for PCI bridges since a child > PCI endpoint may choose to have a device tree node created. > > This patch series is made up of two patches. > > The first patch is adding OF interface to allocate an OF node. It is copied > from: > https://lore.kernel.org/lkml/20220620104123.341054-5-clement.leger@xxxxxxxxxxx/ > > The second patch introduces a kernel option, CONFIG_PCI_OF. When the option > is turned on, the kernel will generate device tree nodes for all PCI > bridges unconditionally. The patch also shows how to use the PCI quirks > infrastructure, DECLARE_PCI_FIXUP_FINAL to generate a device tree node for > a device. Specifically, the patch generates a device tree node for Xilinx > Alveo U50 PCIe accelerator device. The generated device tree nodes do not > have any property. Future patches will add the necessary properties. > > Clément Léger (1): > of: dynamic: add of_node_alloc() > > Lizhi Hou (1): > pci: create device tree node for selected devices > > drivers/of/dynamic.c | 50 +++++++++++++---- > drivers/pci/Kconfig | 11 ++++ > drivers/pci/bus.c | 2 + > drivers/pci/msi/irqdomain.c | 6 +- > drivers/pci/of.c | 106 ++++++++++++++++++++++++++++++++++++ > drivers/pci/pci-driver.c | 3 +- > drivers/pci/pci.h | 16 ++++++ > drivers/pci/quirks.c | 11 ++++ > drivers/pci/remove.c | 1 + > include/linux/of.h | 7 +++ > 10 files changed, 200 insertions(+), 13 deletions(-) > > -- > 2.27.0 >
