* [PATCH v1] driver core/ACPI: Introduce companion_bus_register()
@ 2026-09-06 16:03 Rafael J. Wysocki
2026-09-07 8:23 ` Rafael J. Wysocki (Intel)
0 siblings, 1 reply; 2+ messages in thread
From: Rafael J. Wysocki @ 2026-09-06 16:03 UTC (permalink / raw)
To: Danilo Krummrich, Greg Kroah-Hartman
Cc: Linux ACPI, LKML, Linux Driver Core Development
From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
The ACPI bus type does not allow drivers to be registered, so the sysfs
attributes related to drivers created for it and its devices are
useless, and its drivers/ directory is always empty. All of that is
confusing and wasteful.
To allow skipping the creation of those sysfs attributes, introduce
the concept of a "companion" bus (as a bus without drivers whose
devices can be bound to other devices and used by their drivers) and
add a special registration function for registering "companion" bus
types, companion_bus_register().
Use that function for registering the ACPI bus type.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
drivers/acpi/bus.c | 8 -----
drivers/base/bus.c | 66 ++++++++++++++++++++++++++++++++-------------
include/linux/device/bus.h | 1
3 files changed, 49 insertions(+), 26 deletions(-)
--- a/drivers/acpi/bus.c
+++ b/drivers/acpi/bus.c
@@ -1120,11 +1120,6 @@ EXPORT_SYMBOL_GPL(acpi_driver_match_devi
ACPI Bus operations
-------------------------------------------------------------------------- */
-static int acpi_bus_match(struct device *dev, const struct device_driver *drv)
-{
- return 0;
-}
-
static int acpi_device_uevent(const struct device *dev, struct kobj_uevent_env *env)
{
return __acpi_device_uevent_modalias(to_acpi_device(dev), env);
@@ -1132,7 +1127,6 @@ static int acpi_device_uevent(const stru
const struct bus_type acpi_bus_type = {
.name = "acpi",
- .match = acpi_bus_match,
.uevent = acpi_device_uevent,
};
@@ -1451,7 +1445,7 @@ static int __init acpi_bus_init(void)
*/
acpi_root_dir = proc_mkdir(ACPI_BUS_FILE_ROOT, NULL);
- result = bus_register(&acpi_bus_type);
+ result = companion_bus_register(&acpi_bus_type);
if (!result)
return 0;
--- a/drivers/base/bus.c
+++ b/drivers/base/bus.c
@@ -735,7 +735,7 @@ int bus_add_driver(struct device_driver
struct driver_private *priv;
int error = 0;
- if (!sp)
+ if (!sp || !sp->drivers_kset)
return -EINVAL;
/*
@@ -930,15 +930,7 @@ static ssize_t bus_uevent_store(const st
static struct bus_attribute bus_attr_uevent = __ATTR(uevent, 0200, NULL,
bus_uevent_store);
-/**
- * bus_register - register a driver-core subsystem
- * @bus: bus to register
- *
- * Once we have that, we register the bus with the kobject
- * infrastructure, then register the children subsystems it has:
- * the devices and drivers that belong to the subsystem.
- */
-int bus_register(const struct bus_type *bus)
+static int bus_register_internal(const struct bus_type *bus, bool use_drivers)
{
int retval;
struct subsys_private *priv;
@@ -960,7 +952,7 @@ int bus_register(const struct bus_type *
bus_kobj->kset = bus_kset;
bus_kobj->ktype = &bus_ktype;
- priv->drivers_autoprobe = 1;
+ priv->drivers_autoprobe = use_drivers;
retval = kset_register(&priv->subsys);
if (retval)
@@ -976,10 +968,12 @@ int bus_register(const struct bus_type *
goto bus_devices_fail;
}
- priv->drivers_kset = kset_create_and_add("drivers", NULL, bus_kobj);
- if (!priv->drivers_kset) {
- retval = -ENOMEM;
- goto bus_drivers_fail;
+ if (use_drivers) {
+ priv->drivers_kset = kset_create_and_add("drivers", NULL, bus_kobj);
+ if (!priv->drivers_kset) {
+ retval = -ENOMEM;
+ goto bus_drivers_fail;
+ }
}
INIT_LIST_HEAD(&priv->interfaces);
@@ -989,9 +983,11 @@ int bus_register(const struct bus_type *
klist_init(&priv->klist_devices, klist_devices_get, klist_devices_put);
klist_init(&priv->klist_drivers, NULL, NULL);
- retval = add_probe_files(bus);
- if (retval)
- goto bus_probe_files_fail;
+ if (use_drivers) {
+ retval = add_probe_files(bus);
+ if (retval)
+ goto bus_probe_files_fail;
+ }
retval = sysfs_create_groups(bus_kobj, bus->bus_groups);
if (retval)
@@ -1016,9 +1012,41 @@ out:
kfree(priv);
return retval;
}
+
+/**
+ * bus_register - register a driver-core subsystem
+ * @bus: bus to register
+ *
+ * Once we have that, we register the bus with the kobject
+ * infrastructure, then register the children subsystems it has:
+ * the devices and drivers that belong to the subsystem.
+ */
+int bus_register(const struct bus_type *bus)
+{
+ return bus_register_internal(bus, true);
+}
EXPORT_SYMBOL_GPL(bus_register);
/**
+ * companion_bus_register - register a companion bus type
+ * @bus: companion bus to register
+ *
+ * A companion bus is a bus without drivers. Devices that belong to it can be
+ * bound to other devices as their "companions" and represent interfaces that
+ * can be used by the drivers of those other devices. They may also be used for
+ * the enumeration of those other devices.
+ *
+ * The ACPI bus is a specific example of a companion bus.
+ *
+ * Registering a companion bus is like registering a regular bus except that it
+ * skips the creation of sysfs interfaces related to drivers for @bus.
+ */
+int companion_bus_register(const struct bus_type *bus)
+{
+ return bus_register_internal(bus, false);
+}
+
+/**
* bus_unregister - remove a bus from the system
* @bus: bus.
*
@@ -1412,7 +1440,7 @@ struct device_driver *driver_find(const
struct kobject *k;
struct driver_private *priv;
- if (!sp)
+ if (!sp || !sp->drivers_kset)
return NULL;
k = kset_find_obj(sp->drivers_kset, name);
--- a/include/linux/device/bus.h
+++ b/include/linux/device/bus.h
@@ -113,6 +113,7 @@ struct bus_type {
bool need_parent_lock;
};
+int __must_check companion_bus_register(const struct bus_type *bus);
int __must_check bus_register(const struct bus_type *bus);
void bus_unregister(const struct bus_type *bus);
^ permalink raw reply [flat|nested] 2+ messages in thread* Re: [PATCH v1] driver core/ACPI: Introduce companion_bus_register()
2026-09-06 16:03 [PATCH v1] driver core/ACPI: Introduce companion_bus_register() Rafael J. Wysocki
@ 2026-09-07 8:23 ` Rafael J. Wysocki (Intel)
0 siblings, 0 replies; 2+ messages in thread
From: Rafael J. Wysocki (Intel) @ 2026-09-07 8:23 UTC (permalink / raw)
To: Danilo Krummrich, Greg Kroah-Hartman
Cc: Linux ACPI, LKML, Linux Driver Core Development
On Sun, Sep 6, 2026 at 6:03 PM Rafael J. Wysocki <rafael@kernel.org> wrote:
>
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>
> The ACPI bus type does not allow drivers to be registered, so the sysfs
> attributes related to drivers created for it and its devices are
> useless, and its drivers/ directory is always empty. All of that is
> confusing and wasteful.
>
> To allow skipping the creation of those sysfs attributes, introduce
> the concept of a "companion" bus (as a bus without drivers whose
> devices can be bound to other devices and used by their drivers) and
> add a special registration function for registering "companion" bus
> types, companion_bus_register().
>
> Use that function for registering the ACPI bus type.
>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---
> drivers/acpi/bus.c | 8 -----
> drivers/base/bus.c | 66 ++++++++++++++++++++++++++++++++-------------
> include/linux/device/bus.h | 1
> 3 files changed, 49 insertions(+), 26 deletions(-)
>
> --- a/drivers/acpi/bus.c
> +++ b/drivers/acpi/bus.c
> @@ -1120,11 +1120,6 @@ EXPORT_SYMBOL_GPL(acpi_driver_match_devi
> ACPI Bus operations
> -------------------------------------------------------------------------- */
>
> -static int acpi_bus_match(struct device *dev, const struct device_driver *drv)
> -{
> - return 0;
> -}
> -
> static int acpi_device_uevent(const struct device *dev, struct kobj_uevent_env *env)
> {
> return __acpi_device_uevent_modalias(to_acpi_device(dev), env);
> @@ -1132,7 +1127,6 @@ static int acpi_device_uevent(const stru
>
> const struct bus_type acpi_bus_type = {
> .name = "acpi",
> - .match = acpi_bus_match,
> .uevent = acpi_device_uevent,
> };
>
> @@ -1451,7 +1445,7 @@ static int __init acpi_bus_init(void)
> */
> acpi_root_dir = proc_mkdir(ACPI_BUS_FILE_ROOT, NULL);
>
> - result = bus_register(&acpi_bus_type);
> + result = companion_bus_register(&acpi_bus_type);
> if (!result)
> return 0;
>
> --- a/drivers/base/bus.c
> +++ b/drivers/base/bus.c
> @@ -735,7 +735,7 @@ int bus_add_driver(struct device_driver
> struct driver_private *priv;
> int error = 0;
>
> - if (!sp)
> + if (!sp || !sp->drivers_kset)
This will leak the reference to sp if sp itself is not NULL, but
sp->drivers_kset is (as dutifully reported by Sashiko).
> return -EINVAL;
>
> /*
> @@ -930,15 +930,7 @@ static ssize_t bus_uevent_store(const st
> static struct bus_attribute bus_attr_uevent = __ATTR(uevent, 0200, NULL,
> bus_uevent_store);
>
> -/**
> - * bus_register - register a driver-core subsystem
> - * @bus: bus to register
> - *
> - * Once we have that, we register the bus with the kobject
> - * infrastructure, then register the children subsystems it has:
> - * the devices and drivers that belong to the subsystem.
> - */
> -int bus_register(const struct bus_type *bus)
> +static int bus_register_internal(const struct bus_type *bus, bool use_drivers)
> {
> int retval;
> struct subsys_private *priv;
> @@ -960,7 +952,7 @@ int bus_register(const struct bus_type *
>
> bus_kobj->kset = bus_kset;
> bus_kobj->ktype = &bus_ktype;
> - priv->drivers_autoprobe = 1;
> + priv->drivers_autoprobe = use_drivers;
>
> retval = kset_register(&priv->subsys);
> if (retval)
> @@ -976,10 +968,12 @@ int bus_register(const struct bus_type *
> goto bus_devices_fail;
> }
>
> - priv->drivers_kset = kset_create_and_add("drivers", NULL, bus_kobj);
> - if (!priv->drivers_kset) {
> - retval = -ENOMEM;
> - goto bus_drivers_fail;
> + if (use_drivers) {
> + priv->drivers_kset = kset_create_and_add("drivers", NULL, bus_kobj);
> + if (!priv->drivers_kset) {
> + retval = -ENOMEM;
> + goto bus_drivers_fail;
> + }
> }
>
> INIT_LIST_HEAD(&priv->interfaces);
> @@ -989,9 +983,11 @@ int bus_register(const struct bus_type *
> klist_init(&priv->klist_devices, klist_devices_get, klist_devices_put);
> klist_init(&priv->klist_drivers, NULL, NULL);
>
> - retval = add_probe_files(bus);
> - if (retval)
> - goto bus_probe_files_fail;
> + if (use_drivers) {
> + retval = add_probe_files(bus);
> + if (retval)
> + goto bus_probe_files_fail;
> + }
>
> retval = sysfs_create_groups(bus_kobj, bus->bus_groups);
> if (retval)
> @@ -1016,9 +1012,41 @@ out:
> kfree(priv);
> return retval;
> }
> +
> +/**
> + * bus_register - register a driver-core subsystem
> + * @bus: bus to register
> + *
> + * Once we have that, we register the bus with the kobject
> + * infrastructure, then register the children subsystems it has:
> + * the devices and drivers that belong to the subsystem.
> + */
> +int bus_register(const struct bus_type *bus)
> +{
> + return bus_register_internal(bus, true);
> +}
> EXPORT_SYMBOL_GPL(bus_register);
>
> /**
> + * companion_bus_register - register a companion bus type
> + * @bus: companion bus to register
> + *
> + * A companion bus is a bus without drivers. Devices that belong to it can be
> + * bound to other devices as their "companions" and represent interfaces that
> + * can be used by the drivers of those other devices. They may also be used for
> + * the enumeration of those other devices.
> + *
> + * The ACPI bus is a specific example of a companion bus.
> + *
> + * Registering a companion bus is like registering a regular bus except that it
> + * skips the creation of sysfs interfaces related to drivers for @bus.
> + */
> +int companion_bus_register(const struct bus_type *bus)
> +{
> + return bus_register_internal(bus, false);
> +}
> +
> +/**
> * bus_unregister - remove a bus from the system
> * @bus: bus.
> *
> @@ -1412,7 +1440,7 @@ struct device_driver *driver_find(const
> struct kobject *k;
> struct driver_private *priv;
>
> - if (!sp)
> + if (!sp || !sp->drivers_kset)
And same here, so I will send a v2.
Nevertheless, if you have any concerns or comments on this other than
the above, please let me know.
> return NULL;
>
> k = kset_find_obj(sp->drivers_kset, name);
> --- a/include/linux/device/bus.h
> +++ b/include/linux/device/bus.h
> @@ -113,6 +113,7 @@ struct bus_type {
> bool need_parent_lock;
> };
>
> +int __must_check companion_bus_register(const struct bus_type *bus);
> int __must_check bus_register(const struct bus_type *bus);
>
> void bus_unregister(const struct bus_type *bus);
^ permalink raw reply [flat|nested] 2+ messages in thread
end of thread, other threads:[~2026-09-07 8:24 UTC | newest]
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