linux-kernel - Re: [Q] devicetree overlays

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Date:   Wed, 12 Aug 2020 15:27:47 +0200
From:   "Enrico Weigelt, metux IT consult" <lkml@...ux.net>
To:     Sven Van Asbroeck <thesven73@...il.com>,
        "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

On 07.08.20 16:17, Sven Van Asbroeck wrote:

Hi,

> 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

Thanks, that looks good.

But I've still got another problem: how can I use DT along w/ ACPI ?

The scenario goes like this:

* machine boots and probes normally w/ ACPI
* device is detected via USB, PCI, DMI, etc -> driver gets active
* driver loads (or carries) a DT snippet
* devices on the bus are instantiated via this DT snippet

(driver could also be some udev vodoo)

Example a:

* generic usb i2c dongle w/ some i2c devices attached behind it
* config (or DT snippet) somewhere in the FS

Example b:

* x86 board driver (eg. apu2/3/4), probed via DMI
* just instantiates a bunch of generic drivers and wires up
  devices (gpio, leds, keys, ...)


Do you think we can already do that ?
Otherwise, what has to be done to achieve that ?	


--mtx

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Enrico Weigelt, metux IT consult
Free software and Linux embedded engineering
info@...ux.net -- +49-151-27565287