linux-kernel - Re: [PATCH RFC 0/4] Adding DT functionality to w1 busses

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Message-ID: <CAL_JsqLfzfJC=_NhJy=jFAqEgfi=cvjMcnkjdHdzfM2uhKGBAQ@mail.gmail.com>
Date:   Tue, 26 Jun 2018 15:39:04 -0600
From:   Rob Herring <robh+dt@...nel.org>
To:     Daniel Mack <daniel@...que.org>
Cc:     zbr@...emap.net, Mark Rutland <mark.rutland@....com>,
        szabolcs.gyurko@....hu, devicetree@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC 0/4] Adding DT functionality to w1 busses

On Tue, Jun 19, 2018 at 3:27 PM, Daniel Mack <daniel@...que.org> wrote:
> In order to fully move battery-supplied devices over to devicetree, the
> onewire subsystem must get some updates.
>
> Currently, the w1 bus system works like this. Device families, such as
> battery controllers etc, are registered to the w1 core. Once a master
> device is probed, it starts scanning the bus. Slave devices that are
> revealed through this scan and that match previously registered
> families are then registered, and their .add_slave() callback is
> invoked.
>
> Some devices, such as the ds2760, use that callback to call
> platform_device_alloc() at runtime with a fixed device name to
> instanciate their only user. That user does the actual work, while the
> slave device merely functions as an I/O proxy. In the user
> implementation, the w1 slave device is accessible through
> dev->parent.

Looks to me like you are letting the driver structure define the DT
structure. This detail is all irrelevant to DT.

>
> Now, for devicetree environments, this has to change a bit. First, slave
> devices need to have a matching table so they can be listed as sub-nodes
> of their master bus controller. Second, the core needs to match the
> entries in these tables against the sub-nodes of the master node.
> These two are trivial to do.
>
> The next question is how the w1 slave device and its user(s) are linked
> together. I'm proposing a DT layout with the following example:
>
>         onewire {
>                 compatible = "w1-gpio";
>
>                 w1_slave: slave@0 {
>                         compatible = "maxim,w1-ds2760";
>                 };
>         };
>
>         battery-supply {
>                 compatible = "maxim,ds2760-supply";
>                 w1-slave = <&w1_slave>;
>         };

This should just be one node and a child of the 1-wire master.

Rob