Date:   Wed, 21 Jun 2023 15:23:40 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Lizhi Hou <lizhi.hou@....com>
Cc:     linux-pci@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, robh@...nel.org, max.zhen@....com,
        sonal.santan@....com, stefano.stabellini@...inx.com
Subject: Re: [PATCH V9 0/5] Generate device tree node for pci devices

On Wed, Jun 21, 2023 at 10:34:04AM -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. Second, it allows reuse of a OF
> compatible driver -- often used in SoC platforms -- in a PCI host based
> system.
> 
> There are 2 series devices rely on this patch:
> 
>   1) Xilinx Alveo Accelerator cards (FPGA based device)
>   2) Microchip LAN9662 Ethernet Controller
> 
>      Please see: https://lore.kernel.org/lkml/20220427094502.456111-1-clement.leger@bootlin.com/
> 
> 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.
> 
> 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@gmail.com/
> https://lore.kernel.org/lkml/20220216050056.311496-1-lizhi.hou@xilinx.com/
> 
> 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 three patches.
> 
> The first patch is adding OF interface to create or destroy OF node
> dynamically.
> 
> The second patch introduces a kernel option, CONFIG_DYNAMIC_PCI_OF_NODEX.

In case this log becomes part of the merge commit or something,

s/CONFIG_DYNAMIC_PCI_OF_NODEX/CONFIG_PCI_DYNAMIC_OF_NODES/

> 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.
> 
> The third patch adds basic properties ('reg', 'compatible' and
> 'device_type') to the dynamically generated device tree nodes. More
> properties can be added in the future.
> 
> Here is the example of device tree nodes generated within the ARM64 QEMU.

It's not obvious to me what was there originally and what was added
because of this series.

> # lspci -t
> -[0000:00]-+-00.0
>            +-01.0
>            +-03.0-[01-03]----00.0-[02-03]----00.0-[03]----00.0
>            +-03.1-[04]--
>            \-04.0-[05-06]----00.0-[06]--
> # tree /sys/firmware/devicetree/base/pcie\@10000000
> /sys/firmware/devicetree/base/pcie@...00000
> |-- #address-cells
> |-- #interrupt-cells
> |-- #size-cells
> |-- bus-range
> |-- compatible
> |-- device_type
> |-- dma-coherent
> |-- interrupt-map
> |-- interrupt-map-mask
> |-- linux,pci-domain
> |-- msi-map
> |-- name
> |-- pci@3,0
> |   |-- #address-cells
> |   |-- #size-cells
> |   |-- compatible
> |   |-- device_type
> |   |-- pci@0,0
> |   |   |-- #address-cells
> |   |   |-- #size-cells
> |   |   |-- compatible
> |   |   |-- device_type
> |   |   |-- pci@0,0
> |   |   |   |-- #address-cells
> |   |   |   |-- #size-cells
> |   |   |   |-- compatible
> |   |   |   |-- dev@0,0
> |   |   |   |   |-- #address-cells
> |   |   |   |   |-- #size-cells
> |   |   |   |   |-- compatible
> |   |   |   |   |-- ranges
> |   |   |   |   `-- reg
> |   |   |   |-- device_type
> |   |   |   |-- ranges
> |   |   |   `-- reg
> |   |   |-- ranges
> |   |   `-- reg
> |   |-- ranges
> |   `-- reg
> |-- pci@3,1
> |   |-- #address-cells
> |   |-- #size-cells
> |   |-- compatible
> |   |-- device_type
> |   |-- ranges
> |   `-- reg
> |-- pci@4,0
> |   |-- #address-cells
> |   |-- #size-cells
> |   |-- compatible
> |   |-- device_type
> |   |-- pci@0,0
> |   |   |-- #address-cells
> |   |   |-- #size-cells
> |   |   |-- compatible
> |   |   |-- device_type
> |   |   |-- ranges
> |   |   `-- reg
> |   |-- ranges
> |   `-- reg
> |-- ranges
> `-- reg

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