Re: [PATCH v3] driver core/ACPI: Introduce companion_bus_register()

[Rafael J. Wysocki (Intel)]

On Fri, Sep 25, 2026 at 6:38 PM Michael Kelley <mhklinux@xxxxxxxxxxx> wrote:
>
> From: Rafael J. Wysocki <rafael@xxxxxxxxxx> Sent: Friday, September 25, 2026 2:24 AM
> >
> > The ACPI bus type does not allow drivers to be matched to devices, so
> > the sysfs attributes related to drivers created for it are useless and
> > their existence is confusing.
> >
> > Moreover, it is better to prevent drivers from being registered and
> > looked up for a bus like that.
> >
> > To allow skipping the creation of those sysfs attributes and preventing
> > driver registration and lookup for the ACPI bus type, introduce a
> > "companion" bus type concept and add a special registration function
> > for registering "companion" bus types, companion_bus_register().
> >
> > The "drivers" directory under the ACPI bus type is still needed because
> > there are versions of systemd that depend on it [1].
> >
> > Link: https://lore.kernel.org/linux-acpi/SN6PR02MB41575266A4580339E186E5D9D4812@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/ [1]
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> > Acked-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
>
> Tested this against 7.3.0-rc2, running on my Ubuntu 20.04 instance
> with the older systemd, and as a Hyper-V guest. The VM booted
> as expected, whereas the boot failed with v2 of this patch.
>
> Tested-by: Michael Kelley <mhklinux@xxxxxxxxxxx>
> Reviewed-by: Michael Kelley <mhklinux@xxxxxxxxxxx>

Thank you!