thermal: netlink: Add genetlink bind/unbind notifications

Introduce a new feature to the thermal netlink framework, enabling the
registration of sub drivers to receive events via a notifier mechanism.
Specifically, implement genetlink family bind and unbind callbacks to send
BIND and UNBIND events.

The primary purpose of this enhancement is to facilitate the tracking of
user-space consumers by the Intel HFI driver. By leveraging these
notifications, the driver can determine when consumers are present
or absent.

Suggested-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Stanislaw Gruszka <stanislaw.gruszka@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/thermal/thermal_netlink.c

@@ -7,17 +7,13 @@
  * Generic netlink for thermal management framework
  */
 #include <linux/module.h>
+#include <linux/notifier.h>
 #include <linux/kernel.h>
 #include <net/genetlink.h>
 #include <uapi/linux/thermal.h>
 
 #include "thermal_core.h"
 
-enum thermal_genl_multicast_groups {
-	THERMAL_GENL_SAMPLING_GROUP = 0,
-	THERMAL_GENL_EVENT_GROUP = 1,
-};
-
 static const struct genl_multicast_group thermal_genl_mcgrps[] = {
 	[THERMAL_GENL_SAMPLING_GROUP] = { .name = THERMAL_GENL_SAMPLING_GROUP_NAME, },
 	[THERMAL_GENL_EVENT_GROUP]  = { .name = THERMAL_GENL_EVENT_GROUP_NAME,  },
@@ -75,6 +71,7 @@ struct param {
 typedef int (*cb_t)(struct param *);
 
 static struct genl_family thermal_gnl_family;
+static BLOCKING_NOTIFIER_HEAD(thermal_genl_chain);
 
 static int thermal_group_has_listeners(enum thermal_genl_multicast_groups group)
 {
@@ -645,6 +642,27 @@ out_free_msg:
 	return ret;
 }
 
+static int thermal_genl_bind(int mcgrp)
+{
+	struct thermal_genl_notify n = { .mcgrp = mcgrp };
+
+	if (WARN_ON_ONCE(mcgrp > THERMAL_GENL_MAX_GROUP))
+		return -EINVAL;
+
+	blocking_notifier_call_chain(&thermal_genl_chain, THERMAL_NOTIFY_BIND, &n);
+	return 0;
+}
+
+static void thermal_genl_unbind(int mcgrp)
+{
+	struct thermal_genl_notify n = { .mcgrp = mcgrp };
+
+	if (WARN_ON_ONCE(mcgrp > THERMAL_GENL_MAX_GROUP))
+		return;
+
+	blocking_notifier_call_chain(&thermal_genl_chain, THERMAL_NOTIFY_UNBIND, &n);
+}
+
 static const struct genl_small_ops thermal_genl_ops[] = {
 	{
 		.cmd = THERMAL_GENL_CMD_TZ_GET_ID,
@@ -679,6 +697,8 @@ static struct genl_family thermal_gnl_family __ro_after_init = {
 	.version	= THERMAL_GENL_VERSION,
 	.maxattr	= THERMAL_GENL_ATTR_MAX,
 	.policy		= thermal_genl_policy,
+	.bind		= thermal_genl_bind,
+	.unbind		= thermal_genl_unbind,
 	.small_ops	= thermal_genl_ops,
 	.n_small_ops	= ARRAY_SIZE(thermal_genl_ops),
 	.resv_start_op	= THERMAL_GENL_CMD_CDEV_GET + 1,
@@ -686,6 +706,16 @@ static struct genl_family thermal_gnl_family __ro_after_init = {
 	.n_mcgrps	= ARRAY_SIZE(thermal_genl_mcgrps),
 };
 
+int thermal_genl_register_notifier(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_register(&thermal_genl_chain, nb);
+}
+
+int thermal_genl_unregister_notifier(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_unregister(&thermal_genl_chain, nb);
+}
+
 int __init thermal_netlink_init(void)
 {
 	return genl_register_family(&thermal_gnl_family);

drivers/thermal/thermal_netlink.h

@@ -10,6 +10,19 @@ struct thermal_genl_cpu_caps {
 	int efficiency;
 };
 
+enum thermal_genl_multicast_groups {
+	THERMAL_GENL_SAMPLING_GROUP = 0,
+	THERMAL_GENL_EVENT_GROUP = 1,
+	THERMAL_GENL_MAX_GROUP = THERMAL_GENL_EVENT_GROUP,
+};
+
+#define THERMAL_NOTIFY_BIND	0
+#define THERMAL_NOTIFY_UNBIND	1
+
+struct thermal_genl_notify {
+	int mcgrp;
+};
+
 struct thermal_zone_device;
 struct thermal_trip;
 struct thermal_cooling_device;
@@ -18,6 +31,9 @@ struct thermal_cooling_device;
 #ifdef CONFIG_THERMAL_NETLINK
 int __init thermal_netlink_init(void);
 void __init thermal_netlink_exit(void);
+int thermal_genl_register_notifier(struct notifier_block *nb);
+int thermal_genl_unregister_notifier(struct notifier_block *nb);
+
 int thermal_notify_tz_create(const struct thermal_zone_device *tz);
 int thermal_notify_tz_delete(const struct thermal_zone_device *tz);
 int thermal_notify_tz_enable(const struct thermal_zone_device *tz);
@@ -48,6 +64,16 @@ static inline int thermal_notify_tz_create(const struct thermal_zone_device *tz)
 	return 0;
 }
 
+static inline int thermal_genl_register_notifier(struct notifier_block *nb)
+{
+	return 0;
+}
+
+static inline int thermal_genl_unregister_notifier(struct notifier_block *nb)
+{
+	return 0;
+}
+
 static inline int thermal_notify_tz_delete(const struct thermal_zone_device *tz)
 {
 	return 0;