linux-kernel - Re: [PATCH 0/6] Add support for the root PCI bus device-tree node creation.

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Message-ID: <20241104201507.GA361448-robh@kernel.org>
Date: Mon, 4 Nov 2024 14:15:07 -0600
From: Rob Herring <robh@...nel.org>
To: Herve Codina <herve.codina@...tlin.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Saravana Kannan <saravanak@...gle.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>, Lizhi Hou <lizhi.hou@....com>,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
	linux-pci@...r.kernel.org,
	Allan Nielsen <allan.nielsen@...rochip.com>,
	Horatiu Vultur <horatiu.vultur@...rochip.com>,
	Steen Hegelund <steen.hegelund@...rochip.com>,
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH 0/6] Add support for the root PCI bus device-tree node
 creation.

On Mon, Nov 04, 2024 at 06:19:54PM +0100, Herve Codina wrote:
> Hi,
> 
> This series adds support for creating a device-tree node for a root PCI
> bus on non device-tree based system.
> 
> Creating device-tree nodes for PCI devices already exists upstream. It
> was added in commit 407d1a51921e ("PCI: Create device tree node for
> bridge"). Created device-tree nodes need a parent node to be attached
> to. For the first level devices, on device-tree based system, this
> parent node (i.e. the root PCI bus) is described in the base device-tree
> (PCI controller).
> 
> The LAN966x PCI device driver was recently accepted [1] and relies on
> this feature.
> 
> On system where the base hardware is not described by a device-tree, the
> root PCI bus node to which first level created PCI devices need to be
> attach to does not exist. This is the case for instance on ACPI
> described systems such as x86.
> 
> This series goal is to handle this case.
> 
> In order to have the root PCI bus device-tree node available even on
> x86, this top level node is created (if not already present) based on
> information computed by the PCI core. It follows the same mechanism as
> the one used for PCI devices device-tree node creation.
> 
> In order to have this feature available, a number of changes are needed:
>   - Patch 1 and 2: Introduce and use device_{add,remove}_of_node().
>     This function will also be used in the root PCI bus node creation.
> 
>   - Patch 3 and 4: Improve existing functions to reuse them in the root
>     PCI bus node creation.
> 
>   - Patch 5: Update the default value used when #address-cells is not
>     available in the device-tree root node.
> 
>   - Patch 6: The root PCI bus device-tree node creation itself.
> 
> With those modifications, the LAN966x PCI device is working on x86 systems.

That's nice, but I don't have a LAN966x device nor do I want one. We 
already have the QEMU PCI test device working with the existing PCI 
support. Please ensure this series works with it as well.

Rob