platform/surface: aggregator: Add dedicated bus and device type

The Surface Aggregator EC provides varying functionality, depending on
the Surface device. To manage this functionality, we use dedicated
client devices for each subsystem or virtual device of the EC. While
some of these clients are described as standard devices in ACPI and the
corresponding client drivers can be implemented as platform drivers in
the kernel (making use of the controller API already present), many
devices, especially on newer Surface models, cannot be found there.

To simplify management of these devices, we introduce a new bus and
client device type for the Surface Aggregator subsystem. The new device
type takes care of managing the controller reference, essentially
guaranteeing its validity for as long as the client device exists, thus
alleviating the need to manually establish device links for that purpose
in the client driver (as has to be done with the platform devices).

Signed-off-by: Maximilian Luz <[email protected]>
Reviewed-by: Hans de Goede <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Hans de Goede <[email protected]>

drivers/platform/surface/aggregator/Kconfig

@@ -41,6 +41,18 @@ menuconfig SURFACE_AGGREGATOR
 	  module, y if you want to build it into the kernel and n if you don't
 	  want it at all.
 
+config SURFACE_AGGREGATOR_BUS
+	bool "Surface System Aggregator Module Bus"
+	depends on SURFACE_AGGREGATOR
+	default y
+	help
+	  Expands the Surface System Aggregator Module (SSAM) core driver by
+	  providing a dedicated bus and client-device type.
+
+	  This bus and device type are intended to provide and simplify support
+	  for non-platform and non-ACPI SSAM devices, i.e. SSAM devices that are
+	  not auto-detectable via the conventional means (e.g. ACPI).
+
 config SURFACE_AGGREGATOR_ERROR_INJECTION
 	bool "Surface System Aggregator Module Error Injection Capabilities"
 	depends on SURFACE_AGGREGATOR

drivers/platform/surface/aggregator/Makefile

@@ -11,3 +11,7 @@ surface_aggregator-objs += ssh_parser.o
 surface_aggregator-objs += ssh_packet_layer.o
 surface_aggregator-objs += ssh_request_layer.o
 surface_aggregator-objs += controller.o
+
+ifeq ($(CONFIG_SURFACE_AGGREGATOR_BUS),y)
+surface_aggregator-objs += bus.o
+endif