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From:   Kai-Heng Feng <kai.heng.feng@canonical.com>
Date:   Thu, 21 Jan 2021 14:22:43 +0800
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Subject: Re: [PATCH] ACPI / device_sysfs: Use OF_MODALIAS for "compatible" modalias
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        AceLan Kao <acelan.kao@canonical.com>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Mika Westerberg <mika.westerberg@linux.intel.com>,
        Len Brown <lenb@kernel.org>,
        "open list:ACPI" <linux-acpi@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>
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On Tue, Jan 19, 2021 at 6:34 PM Greg Kroah-Hartman
<gregkh@linuxfoundation.org> wrote:
>
> On Tue, Jan 19, 2021 at 11:41:59AM +0200, Andy Shevchenko wrote:
> > On Tue, Jan 19, 2021 at 04:41:48PM +0800, Kai-Heng Feng wrote:
> > > On Tue, Jan 19, 2021 at 4:27 PM Greg Kroah-Hartman
> > > <gregkh@linuxfoundation.org> wrote:
> > > > On Tue, Jan 19, 2021 at 04:15:13PM +0800, Kai-Heng Feng wrote:
> >
> > ...
> >
> > > > Who will use OF_MODALIAS and where have you documented it?
> > >
> > > After this lands in mainline, I'll modify the pull request for systemd
> > > to add a new rule for OF_MODALIAS.
> > > I'll modify the comment on the function to document the change.
> >
> > I'm wondering why to have two fixes in two places instead of fixing udev to
> > understand multiple MODALIAS= events?
>
> It's not a matter of multiple events, it's a single event with a
> key/value pair with duplicate keys and different values.
>
> What is this event with different values supposed to be doing in
> userspace?  Do you want multiple invocations of `modprobe` or something
> else?
>
> Usually a "device" only has a single "signature" that modprobe uses to
> look up the correct module for.  Modules can support any number of
> device signatures, but traditionally it is odd to think that a device
> itself can be supported by multiple modules, which is what you are
> saying is happening here.
>
> So what should userspace do with this, and why does a device need to
> have multiple module alias signatures?

From the original use case [1], I think the "compatible" modalias
should be enough.
Andy and Mika, what do you think? Can we remove the ACPI modalias for this case?

[1] https://lwn.net/Articles/612062/

Kai-Heng

>
> thanks,
>
> greg k-h