platform/surface: aggregator: Move subsystem hub drivers to their own module

Split out subsystem device hub drivers into their own module. This
allows us to load the hub drivers separately from the registry, which
will help future DT/OF support.

While doing so, also remove a small bit of code duplication.
Signed-off-by: Maximilian Luz <luzmaximilian@gmail.com>
Link: https://lore.kernel.org/r/20220624205800.1355621-3-luzmaximilian@gmail.comReviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>

MAINTAINERS

@@ -13253,6 +13253,12 @@ F:	include/linux/surface_acpi_notify.h
 F:	include/linux/surface_aggregator/
 F:	include/uapi/linux/surface_aggregator/
 
+MICROSOFT SURFACE SYSTEM AGGREGATOR HUB DRIVER
+M:	Maximilian Luz <luzmaximilian@gmail.com>
+L:	platform-driver-x86@vger.kernel.org
+S:	Maintained
+F:	drivers/platform/surface/surface_aggregator_hub.c
+
 MICROTEK X6 SCANNER
 M:	Oliver Neukum <oliver@neukum.org>
 S:	Maintained

drivers/platform/surface/Kconfig

@@ -72,18 +72,45 @@ config SURFACE_AGGREGATOR_CDEV
 	  The provided interface is intended for debugging and development only,
 	  and should not be used otherwise.
 
+config SURFACE_AGGREGATOR_HUB
+	tristate "Surface System Aggregator Module Subsystem Device Hubs"
+	depends on SURFACE_AGGREGATOR
+	depends on SURFACE_AGGREGATOR_BUS
+	help
+	  Device-hub drivers for Surface System Aggregator Module (SSAM) subsystem
+	  devices.
+
+	  Provides subsystem hub drivers which manage client devices on various
+	  SSAM subsystems. In some subsystems, notably the BAS subsystem managing
+	  devices contained in the base of the Surface Book 3 and the KIP subsystem
+	  managing type-cover devices in the Surface Pro 8 and Surface Pro X,
+	  devices can be (hot-)removed. Hub devices and drivers are required to
+	  manage these subdevices.
+
+	  Devices managed via these hubs are:
+	  - Battery/AC devices (Surface Book 3).
+	  - HID input devices (7th-generation and later models with detachable
+	    input devices).
+
+	  Select M (recommended) or Y here if you want support for the above
+	  mentioned devices on the corresponding Surface models. Without this
+	  module, the respective devices mentioned above will not be instantiated
+	  and thus any functionality provided by them will be missing, even when
+	  drivers for these devices are present. This module only provides the
+	  respective subsystem hubs. Both drivers and device specification (e.g.
+	  via the Surface Aggregator Registry) for these devices still need to be
+	  selected via other options.
+
 config SURFACE_AGGREGATOR_REGISTRY
 	tristate "Surface System Aggregator Module Device Registry"
 	depends on SURFACE_AGGREGATOR
 	depends on SURFACE_AGGREGATOR_BUS
 	help
-	  Device-registry and device-hubs for Surface System Aggregator Module
-	  (SSAM) devices.
+	  Device-registry for Surface System Aggregator Module (SSAM) devices.
 
 	  Provides a module and driver which act as a device-registry for SSAM
 	  client devices that cannot be detected automatically, e.g. via ACPI.
-	  Such devices are instead provided via this registry and attached via
-	  device hubs, also provided in this module.
+	  Such devices are instead provided and managed via this registry.
 
 	  Devices provided via this registry are:
 	  - Platform profile (performance-/cooling-mode) device (5th- and later

drivers/platform/surface/Makefile

@@ -9,6 +9,7 @@ obj-$(CONFIG_SURFACE_3_POWER_OPREGION)	+= surface3_power.o
 obj-$(CONFIG_SURFACE_ACPI_NOTIFY)	+= surface_acpi_notify.o
 obj-$(CONFIG_SURFACE_AGGREGATOR)	+= aggregator/
 obj-$(CONFIG_SURFACE_AGGREGATOR_CDEV)	+= surface_aggregator_cdev.o
+obj-$(CONFIG_SURFACE_AGGREGATOR_HUB)	+= surface_aggregator_hub.o
 obj-$(CONFIG_SURFACE_AGGREGATOR_REGISTRY) += surface_aggregator_registry.o
 obj-$(CONFIG_SURFACE_AGGREGATOR_TABLET_SWITCH) += surface_aggregator_tabletsw.o
 obj-$(CONFIG_SURFACE_DTX)		+= surface_dtx.o