linux-kernel - Re: [PATCH v2 1/2] dt-bindings: google,cros-ec-keyb: Introduce switches only compatible

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Message-ID: <Yn2YvIFNhaz5GmfI@google.com>
Date:   Thu, 12 May 2022 16:31:08 -0700
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     Doug Anderson <dianders@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>, patches@...ts.linux.dev,
        chrome-platform@...ts.linux.dev,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        Benson Leung <bleung@...omium.org>,
        Guenter Roeck <groeck@...omium.org>,
        Hsin-Yi Wang <hsinyi@...omium.org>,
        "Joseph S. Barrera III" <joebar@...omium.org>
Subject: Re: [PATCH v2 1/2] dt-bindings: google,cros-ec-keyb: Introduce
 switches only compatible

On Thu, May 12, 2022 at 01:11:39PM -0700, Stephen Boyd wrote:
> Quoting Stephen Boyd (2022-05-12 11:58:02)
> > Quoting Dmitry Torokhov (2022-05-12 03:22:30)
> > >
> > > Have we solved module loading in the presence of multiple compatibles?
> > > IIRC we only ever try to load module on the first compatible, so you'd
> > > be breaking autoloading cros-ec-keyb on these older kernels. I think the
> > > cure that is being proposed is worse than the disease.
> > >
> >
> > The first compatible is still cros-ec-keyb in the driver though? Or you
> > mean the first compatible in the node? I'm not aware of this problem at
> > all but I can certainly test out a fake node and module and see if it
> > gets autoloaded.
> 
> I can't get this test module to fail to load no matter what I do. I
> commented out the second match table entry, and kept it there and
> removed 'vendor,switch-compat' from the DTS. Module still autoloads.
> 

Ah, indeed, if the module contains both compatibles we will load it. It
is broken when we have 2 or more modules and DT lists several
compatibles for a device.

OK, it looks like you feel very strongly regarding having a dedicated
compatible. In this case please make sure that the compatible's behavior
is properly documented (i.e. google,cros-ec-keyb compatible does not
imply that there are *NO* switches, and users having buttons and
switches in addition to matrix keys can also use google,cros-ec-keyb as
a compatible for their device). We also need to mention that with the
2nd compatible the device still can report key/button events, it is
simply that there is no matrix component. Should we call the other
compatible google,cros-ec-bs?

We should also abort binding the device if it specifies the new
compatible, but EC does not report any buttons or switches.

Thanks.

-- 
Dmitry