linux-kernel - Re: [RFC PATCH v2 0/7] of: Introduce hardware prober driver

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Date:   Thu, 16 Nov 2023 13:07:30 +0800
From:   Chen-Yu Tsai <wenst@...omium.org>
To:     Rob Herring <robh+dt@...nel.org>
Cc:     Doug Anderson <dianders@...omium.org>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Frank Rowand <frowand.list@...il.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Hsin-Yi Wang <hsinyi@...omium.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        andriy.shevchenko@...ux.intel.com, Jiri Kosina <jikos@...nel.org>,
        linus.walleij@...aro.org, broonie@...nel.org,
        gregkh@...uxfoundation.org, hdegoede@...hat.com,
        james.clark@....com, james@...iv.tech, keescook@...omium.org,
        petr.tesarik.ext@...wei.com, rafael@...nel.org, tglx@...utronix.de,
        Jeff LaBundy <jeff@...undy.com>, linux-input@...r.kernel.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Johan Hovold <johan@...nel.org>
Subject: Re: [RFC PATCH v2 0/7] of: Introduce hardware prober driver

On Thu, Nov 16, 2023 at 5:35 AM Rob Herring <robh+dt@...nel.org> wrote:
>
> On Wed, Nov 15, 2023 at 2:45 PM Doug Anderson <dianders@...omium.org> wrote:
> >
> > Hi,
> >
> > On Wed, Nov 15, 2023 at 2:28 PM Rob Herring <robh+dt@...nel.org> wrote:
> > >
> > > > So if we're searching the whole device tree for "failed-needs-probe"
> > > > then we need to figure out which devices are related to each other. If
> > > > a given board has second sources for MIPI panels, touchscreens, and
> > > > trackpads then we need to know which of the "failed-needs-probe"
> > > > devices are trackpads, which are touchscreens, and which are MIPI
> > > > panels. Do you have any suggestions for how we should do that? Maybe
> > > > it was in some other thread that I missed? I guess we could have a
> > > > board-specific table mapping (compatible + node name + reg) to a
> > > > class, but that feels awkward.
> > >
> > > Node name is supposed to correspond to device class, so why not use
> > > that (no path or unit-address.) and nothing else (well, besides
> > > "status")?
> >
> > One problem is that I could imagine having two second source trackpads
> > that both have the same i2c address. That would give them the same
> > name, right? I guess you could maybe come up with some sort of suffix
> > rule? Like
> >
> > trackpad-1@10 {
> >   compatible = "elan,blah";
> >   ret = <0x10>;
> >   status = "failed-needs-probe";
> >   ...
> > }
> > trackpad-2@10 {
> >   compatible = "goodix,gt7375p";
> >   ret = <0x10>;
> >   status = "failed-needs-probe";
> >   ...
> > }
> >
> > Then I guess the class would be "trackpad"?
>
> That issue is somewhat orthogonal because it is not following the spec.
>
> I'm not sure mixing the 2 styles of node names is a good idea. While
> not used too much, matching by node name does ignore the unit-address,
> but I'm not sure we could ignore a '-N'.

of_node_name_prefix() solves that. I assume that's the intended use case?

> I think our options are either add something to the unit-address or
> use i2c-mux binding. Adding to the unit-address is not unprecedented.
> I did that for some of the register bit level bindings where you have
> a node for different bits at the same address. The downside is
> unit-address is bus specific, so we'd have to add that for multiple
> buses. For the i2c-mux, it's perhaps a bit complex and I'm not sure
> what if anything you'd have to do to manage the mux that's not really
> there.
>
> Rob