firmware: arm_scmi: Split bus and driver into distinct modules

Make the SCMI bus on its own as a distinct module initialized at
subsys_initcall level when builtin.

Keep the SCMI driver core stack, together with any configured transport,
in a different module initialized as module_init level.

SCMI drivers initialization remain unchanged at module_init level.
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Link: https://lore.kernel.org/r/20221222185049.737625-10-cristian.marussi@arm.comSigned-off-by: Sudeep Holla <sudeep.holla@arm.com>

drivers/firmware/arm_scmi/Makefile

 # SPDX-License-Identifier: GPL-2.0-only
 scmi-bus-y = bus.o
+scmi-core-objs := $(scmi-bus-y)
+
 scmi-driver-y = driver.o notify.o
 scmi-transport-$(CONFIG_ARM_SCMI_HAVE_SHMEM) = shmem.o
 scmi-transport-$(CONFIG_ARM_SCMI_TRANSPORT_MAILBOX) += mailbox.o
@@ -8,9 +10,11 @@ scmi-transport-$(CONFIG_ARM_SCMI_HAVE_MSG) += msg.o
 scmi-transport-$(CONFIG_ARM_SCMI_TRANSPORT_VIRTIO) += virtio.o
 scmi-transport-$(CONFIG_ARM_SCMI_TRANSPORT_OPTEE) += optee.o
 scmi-protocols-y = base.o clock.o perf.o power.o reset.o sensors.o system.o voltage.o powercap.o
-scmi-module-objs := $(scmi-bus-y) $(scmi-driver-y) $(scmi-protocols-y) \
-		    $(scmi-transport-y)
+scmi-module-objs := $(scmi-driver-y) $(scmi-protocols-y) $(scmi-transport-y)
+
+obj-$(CONFIG_ARM_SCMI_PROTOCOL) += scmi-core.o
 obj-$(CONFIG_ARM_SCMI_PROTOCOL) += scmi-module.o
+
 obj-$(CONFIG_ARM_SCMI_POWER_DOMAIN) += scmi_pm_domain.o
 obj-$(CONFIG_ARM_SCMI_POWER_CONTROL) += scmi_power_control.o
 

drivers/firmware/arm_scmi/bus.c

@@ -476,18 +476,21 @@ static void scmi_devices_unregister(void)
 	bus_for_each_dev(&scmi_bus_type, NULL, NULL, __scmi_devices_unregister);
 }
 
-int __init scmi_bus_init(void)
+static int __init scmi_bus_init(void)
 {
 	int retval;
 
 	retval = bus_register(&scmi_bus_type);
 	if (retval)
-		pr_err("scmi protocol bus register failed (%d)\n", retval);
+		pr_err("SCMI protocol bus register failed (%d)\n", retval);
+
+	pr_info("SCMI protocol bus registered\n");
 
 	return retval;
 }
+subsys_initcall(scmi_bus_init);
 
-void __exit scmi_bus_exit(void)
+static void __exit scmi_bus_exit(void)
 {
 	/*
 	 * Destroy all remaining devices: just in case the drivers were
@@ -497,3 +500,9 @@ void __exit scmi_bus_exit(void)
 	bus_unregister(&scmi_bus_type);
 	ida_destroy(&scmi_bus_id);
 }
+module_exit(scmi_bus_exit);
+
+MODULE_ALIAS("scmi-core");
+MODULE_AUTHOR("Sudeep Holla <sudeep.holla@arm.com>");
+MODULE_DESCRIPTION("ARM SCMI protocol bus");
+MODULE_LICENSE("GPL");

drivers/firmware/arm_scmi/common.h

@@ -99,8 +99,6 @@ scmi_revision_area_get(const struct scmi_protocol_handle *ph);
 void scmi_setup_protocol_implemented(const struct scmi_protocol_handle *ph,
 				     u8 *prot_imp);
 
-int __init scmi_bus_init(void);
-void __exit scmi_bus_exit(void);
 extern struct bus_type scmi_bus_type;
 
 #define SCMI_BUS_NOTIFY_DEVICE_REQUEST		0

drivers/firmware/arm_scmi/driver.c

@@ -2638,8 +2638,6 @@ static int __init scmi_driver_init(void)
 	if (WARN_ON(!IS_ENABLED(CONFIG_ARM_SCMI_HAVE_TRANSPORT)))
 		return -EINVAL;
 
-	scmi_bus_init();
-
 	/* Initialize any compiled-in transport which provided an init/exit */
 	ret = scmi_transports_init();
 	if (ret)
@@ -2658,7 +2656,7 @@ static int __init scmi_driver_init(void)
 
 	return platform_driver_register(&scmi_driver);
 }
-subsys_initcall(scmi_driver_init);
+module_init(scmi_driver_init);
 
 static void __exit scmi_driver_exit(void)
 {
@@ -2673,8 +2671,6 @@ static void __exit scmi_driver_exit(void)
 	scmi_system_unregister();
 	scmi_powercap_unregister();
 
-	scmi_bus_exit();
-
 	scmi_transports_exit();
 
 	platform_driver_unregister(&scmi_driver);