firmware: smccc: Add an Arm SMCCC bus

SMCCC-discovered firmware services are currently represented by separate
platform devices, such as smccc_trng and arm-cca-dev. Those devices do not
represent independent DT/ACPI-described platform resources; they are
features of the SMCCC firmware interface.

Add an Arm SMCCC bus for services discovered through the SMCCC firmware
interface. The bus provides SMCCC device and driver registration
helpers, function ID based matching, modalias generation, and a sysfs
modalias attribute so SMCCC service drivers can bind to discovered
firmware services and autoload as modules.

Follow-up changes can then register SMCCC firmware services as arm-smccc
devices instead of creating independent per-feature platform devices.

Based on arm_ffa code

Reviewed-by: Jonathan Cameron <jonathan.cameron@oss.qualcomm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Sudeep Holla <sudeep.holla@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Lorenzo Pieralisi <lpieralisi@kernel.org>
Cc: Sudeep Holla <sudeep.holla@kernel.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nicolas Schier <nsc@kernel.org>
Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

3 files changed, 68 insertions, 0 deletions

diff --git a/include/linux/arm-smccc-bus.h b/include/linux/arm-smccc-bus.h
new file mode 100644
index 000000000000..05c0c850510e
--- /dev/null
+++ b/include/linux/arm-smccc-bus.h
@@ -0,0 +1,48 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2026 Arm Limited
+ */
+#ifndef __LINUX_ARM_SMCCC_BUS_H
+#define __LINUX_ARM_SMCCC_BUS_H
+
+#include <linux/device.h>
+#include <linux/device-id/arm_smccc.h>
+#include <linux/module.h>
+
+struct arm_smccc_device {
+	struct device dev;
+	u32 func_id;
+};
+
+#define to_arm_smccc_device(d) container_of_const(d, struct arm_smccc_device, dev)
+
+struct arm_smccc_driver {
+	struct device_driver driver;
+
+	const char *name;
+	int (*probe)(struct arm_smccc_device *sdev);
+	void (*remove)(struct arm_smccc_device *sdev);
+	const struct arm_smccc_device_id *id_table;
+};
+
+#define to_arm_smccc_driver(d) \
+	container_of_const(d, struct arm_smccc_driver, driver)
+
+int arm_smccc_driver_register(struct arm_smccc_driver *driver,
+		struct module *owner, const char *mod_name);
+void arm_smccc_driver_unregister(struct arm_smccc_driver *driver);
+struct arm_smccc_device *arm_smccc_device_register(const char *name, u32 func_id);
+void arm_smccc_device_unregister(struct arm_smccc_device *smcc_dev);
+
+#define arm_smccc_register(driver) \
+	arm_smccc_driver_register(driver, THIS_MODULE, KBUILD_MODNAME)
+#define arm_smccc_unregister(driver) \
+	arm_smccc_driver_unregister(driver)
+
+#define module_arm_smccc_driver(__arm_smccc_driver) \
+	module_driver(__arm_smccc_driver, arm_smccc_register, \
+		      arm_smccc_unregister)
+
+extern const struct bus_type arm_smccc_bus_type;
+
+#endif /* __LINUX_ARM_SMCCC_BUS_H */
diff --git a/include/linux/device-id/arm_smccc.h b/include/linux/device-id/arm_smccc.h
new file mode 100644
index 000000000000..a8579832fc1c
--- /dev/null
+++ b/include/linux/device-id/arm_smccc.h
@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __LINUX_DEVICE_ID_ARM_SMCCC_H
+#define __LINUX_DEVICE_ID_ARM_SMCCC_H
+
+#ifdef __KERNEL__
+#include <linux/types.h>
+#endif
+
+#define ARM_SMCCC_MODULE_PREFIX "arm_smccc:"
+
+/**
+ * struct arm_smccc_device_id - Arm SMCCC bus device identifier
+ * @func_id: SMCCC function identifier
+ */
+struct arm_smccc_device_id {
+	__u32 func_id;
+};
+
+#endif /* __LINUX_DEVICE_ID_ARM_SMCCC_H */
diff --git a/include/linux/mod_devicetable.h b/include/linux/mod_devicetable.h
index a397213bedac..318c4b5c3451 100644
--- a/include/linux/mod_devicetable.h
+++ b/include/linux/mod_devicetable.h
@@ -16,6 +16,7 @@
 #include "device-id/amba.h"
 #include "device-id/ap.h"
 #include "device-id/apr.h"
+#include "device-id/arm_smccc.h"
 #include "device-id/auxiliary.h"
 #include "device-id/bcma.h"
 #include "device-id/ccw.h"