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

On Fri Sep 25, 2026 at 11:23 AM CEST, Rafael J. Wysocki wrote:

From: Rafael J. Wysocki <redacted>

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].

Maybe we should also add a brief note above kset_create_and_add("drivers", ...)
why we retain the directory even if !use_drivers.

Link: https://lore.kernel.org/linux-acpi/SN6PR02MB41575266A4580339E186E5D9D4812@SN6PR02MB4157.namprd02.prod.outlook.com/ (local) [1]
Signed-off-by: Rafael J. Wysocki <redacted>

Reviewed-by: Danilo Krummrich <dakr@kernel.org>