On Tue, Feb 04, 2025 at 08:35:00AM +0100, Herve Codina wrote:
> PCI devices device-tree nodes can be already created. This was
> introduced by commit 407d1a51921e ("PCI: Create device tree node for
> bridge").
>
> In order to have device-tree nodes related to PCI devices attached on
> their PCI root bus (the PCI bus handled by the PCI host bridge), a PCI
> root bus device-tree node is needed. This root bus node will be used as
> the parent node of the first level devices scanned on the bus. On
> device-tree based systems, this PCI root bus device tree node is set to
> the node of the related PCI host bridge. The PCI host bridge node is
> available in the device-tree used to describe the hardware passed at
> boot.
>
> On non device-tree based system (such as ACPI), a device-tree node for
> the PCI host bridge or for the root bus does not exist. Indeed, the PCI
> host bridge is not described in a device-tree used at boot simply
> because no device-tree are passed at boot.
>
> The device-tree PCI host bridge node creation needs to be done at
> runtime. This is done in the same way as for the creation of the PCI
> device nodes. I.e. node and properties are created based on computed
> information done by the PCI core. Also, as is done on device-tree based
> systems, this PCI host bridge node is used for the PCI root bus.
This is a detailed low-level description of what this patch does. Can
we include a high level outline of what the benefit is and why we want
this patch?
Based on 185686beb464 ("misc: Add support for LAN966x PCI device"), I
assume the purpose is to deal with some kind of non-standard PCI
topology, e.g., a single B/D/F function contains several different
pieces of functionality to be driven by several different drivers, and
we build a device tree description of those pieces and then bind those
drivers to the functionality using platform_device interfaces?
Bjorn
