linux-kernel - Re: [PATCH] ACPI / device_sysfs: Use OF

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Message-ID: <YAa1ygjr2L3VxBKF@kroah.com>
Date:   Tue, 19 Jan 2021 11:34:50 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Kai-Heng Feng <kai.heng.feng@...onical.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        AceLan Kao <acelan.kao@...onical.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Len Brown <lenb@...nel.org>,
        "open list:ACPI" <linux-acpi@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ACPI / device_sysfs: Use OF_MODALIAS for "compatible"
 modalias

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@...uxfoundation.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?

thanks,

greg k-h