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 <luzmaximilian@gmail.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20201221183959.1186143-7-luzmaximilian@gmail.comSigned-off-by: Hans de Goede <hdegoede@redhat.com>

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

drivers/platform/surface/aggregator/bus.h

+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Surface System Aggregator Module bus and device integration.
+ *
+ * Copyright (C) 2019-2020 Maximilian Luz <luzmaximilian@gmail.com>
+ */
+
+#ifndef _SURFACE_AGGREGATOR_BUS_H
+#define _SURFACE_AGGREGATOR_BUS_H
+
+#include <linux/surface_aggregator/controller.h>
+
+#ifdef CONFIG_SURFACE_AGGREGATOR_BUS
+
+void ssam_controller_remove_clients(struct ssam_controller *ctrl);
+
+int ssam_bus_register(void);
+void ssam_bus_unregister(void);
+
+#else /* CONFIG_SURFACE_AGGREGATOR_BUS */
+
+static inline void ssam_controller_remove_clients(struct ssam_controller *ctrl) {}
+static inline int ssam_bus_register(void) { return 0; }
+static inline void ssam_bus_unregister(void) {}
+
+#endif /* CONFIG_SURFACE_AGGREGATOR_BUS */
+#endif /* _SURFACE_AGGREGATOR_BUS_H */

drivers/platform/surface/aggregator/core.c

@@ -22,6 +22,8 @@
 #include <linux/sysfs.h>
 
 #include <linux/surface_aggregator/controller.h>
+
+#include "bus.h"
 #include "controller.h"
 
 #define CREATE_TRACE_POINTS
@@ -739,6 +741,9 @@ static void ssam_serial_hub_remove(struct serdev_device *serdev)
 	sysfs_remove_group(&serdev->dev.kobj, &ssam_sam_group);
 	ssam_controller_lock(ctrl);
 
+	/* Remove all client devices. */
+	ssam_controller_remove_clients(ctrl);
+
 	/* Act as if suspending to silence events. */
 	status = ssam_ctrl_notif_display_off(ctrl);
 	if (status) {
@@ -791,6 +796,10 @@ static int __init ssam_core_init(void)
 {
 	int status;
 
+	status = ssam_bus_register();
+	if (status)
+		goto err_bus;
+
 	status = ssh_ctrl_packet_cache_init();
 	if (status)
 		goto err_cpkg;
@@ -810,6 +819,8 @@ static int __init ssam_core_init(void)
 err_evitem:
 	ssh_ctrl_packet_cache_destroy();
 err_cpkg:
+	ssam_bus_unregister();
+err_bus:
 	return status;
 }
 module_init(ssam_core_init);
@@ -819,6 +830,7 @@ static void __exit ssam_core_exit(void)
 	serdev_device_driver_unregister(&ssam_serial_hub);
 	ssam_event_item_cache_destroy();
 	ssh_ctrl_packet_cache_destroy();
+	ssam_bus_unregister();
 }
 module_exit(ssam_core_exit);
 

include/linux/mod_devicetable.h

@@ -846,4 +846,22 @@ struct auxiliary_device_id {
 	kernel_ulong_t driver_data;
 };
 
+/* Surface System Aggregator Module */
+
+#define SSAM_MATCH_TARGET	0x1
+#define SSAM_MATCH_INSTANCE	0x2
+#define SSAM_MATCH_FUNCTION	0x4
+
+struct ssam_device_id {
+	__u8 match_flags;
+
+	__u8 domain;
+	__u8 category;
+	__u8 target;
+	__u8 instance;
+	__u8 function;
+
+	kernel_ulong_t driver_data;
+};
+
 #endif /* LINUX_MOD_DEVICETABLE_H */

scripts/mod/devicetable-offsets.c

@@ -246,5 +246,13 @@ int main(void)
 	DEVID(auxiliary_device_id);
 	DEVID_FIELD(auxiliary_device_id, name);
 
+	DEVID(ssam_device_id);
+	DEVID_FIELD(ssam_device_id, match_flags);
+	DEVID_FIELD(ssam_device_id, domain);
+	DEVID_FIELD(ssam_device_id, category);
+	DEVID_FIELD(ssam_device_id, target);
+	DEVID_FIELD(ssam_device_id, instance);
+	DEVID_FIELD(ssam_device_id, function);
+
 	return 0;
 }

scripts/mod/file2alias.c

@@ -1375,6 +1375,28 @@ static int do_auxiliary_entry(const char *filename, void *symval, char *alias)
 	return 1;
 }
 
+/*
+ * Looks like: ssam:dNcNtNiNfN
+ *
+ * N is exactly 2 digits, where each is an upper-case hex digit.
+ */
+static int do_ssam_entry(const char *filename, void *symval, char *alias)
+{
+	DEF_FIELD(symval, ssam_device_id, match_flags);
+	DEF_FIELD(symval, ssam_device_id, domain);
+	DEF_FIELD(symval, ssam_device_id, category);
+	DEF_FIELD(symval, ssam_device_id, target);
+	DEF_FIELD(symval, ssam_device_id, instance);
+	DEF_FIELD(symval, ssam_device_id, function);
+
+	sprintf(alias, "ssam:d%02Xc%02X", domain, category);
+	ADD(alias, "t", match_flags & SSAM_MATCH_TARGET, target);
+	ADD(alias, "i", match_flags & SSAM_MATCH_INSTANCE, instance);
+	ADD(alias, "f", match_flags & SSAM_MATCH_FUNCTION, function);
+
+	return 1;
+}
+
 /* Does namelen bytes of name exactly match the symbol? */
 static bool sym_is(const char *name, unsigned namelen, const char *symbol)
 {
@@ -1450,6 +1472,7 @@ static const struct devtable devtable[] = {
 	{"wmi", SIZE_wmi_device_id, do_wmi_entry},
 	{"mhi", SIZE_mhi_device_id, do_mhi_entry},
 	{"auxiliary", SIZE_auxiliary_device_id, do_auxiliary_entry},
+	{"ssam", SIZE_ssam_device_id, do_ssam_entry},
 };
 
 /* Create MODULE_ALIAS() statements.