linux-kernel - Re: [Q] devicetree overlays

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Message-ID: <CAGngYiVokqYkEiQTcqAMnvif3qEWkPOb1cAk+4rvwgxBKZ5Ukw@mail.gmail.com>
Date:   Fri, 7 Aug 2020 10:17:23 -0400
From:   Sven Van Asbroeck <thesven73@...il.com>
To:     "Enrico Weigelt, metux IT consult" <info@...ux.net>
Cc:     Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
        Frank Rowand <frowand.list@...il.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [Q] devicetree overlays

Hello Enrico,

On Fri, Aug 7, 2020 at 7:27 AM Enrico Weigelt, metux IT consult
<info@...ux.net> wrote:
>
> In both cases it would be nice to have the actual device configuration
> written as a DT snippet, which just needs to be loaded.
>

I believe you're asking: "how do I associate device tree nodes to
devices on a dynamically discoverable bus such as USB or PCI" right ?

I believe that already exists. You can describe the _expected_ pci or
usb topology in the
devicetree. If a device gets detected in a spot on the bus described
in the tree, that
snippet will be automatically associated with this device.

How to for usb:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/usb/usb-device.txt?h=v5.8

How to for pci:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/pci/pci.txt?h=v5.8

For example, associate a mac address to an ethernet controller
on a pcie bus via the devicetree.
"reg" (which describes pcie topology/address) still needs filling in.

&pcie {
        host@0 {
                #address-cells = <3>;
                #size-cells = <2>;
                reg = <0 0 0 0 0>;
                bcm5778: bcm5778@0 {
                        reg = <0 0 0 0 0>;
                        mac-address = [CA 11 AB 1E 10 01];
                };
        };
};