PM: EM: Implement em_notify_pd_deleted()

Add the event notification infrastructure and implement the event
notification for when a performance domain is deleted (EM_CMD_PD_DELETED).

The event contains the ID of the performance domain (EM_A_PD_TABLE_PD_ID)
so the userspace can identify the changed performance domain for further
processing.

Signed-off-by: Changwoo Min <changwoo@igalia.com>
Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>
Link: https://patch.msgid.link/20251020220914.320832-9-changwoo@igalia.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Author: multics69

kernel/power/em_netlink.c

@@ -213,6 +213,50 @@ int em_nl_get_pd_table_doit(struct sk_buff *skb, struct genl_info *info)
 	return ret;
 }
 
+
+/**************************** Event encoding *********************************/
+static int __em_notify_pd_deleted_size(const struct em_perf_domain *pd)
+{
+	int id_sz = nla_total_size(sizeof(u32)); /* EM_A_PD_TABLE_PD_ID */
+
+	return nlmsg_total_size(genlmsg_msg_size(id_sz));
+}
+
+void em_notify_pd_deleted(const struct em_perf_domain *pd)
+{
+	struct sk_buff *msg;
+	void *hdr;
+	int msg_sz;
+
+	if (!genl_has_listeners(&em_nl_family, &init_net, EM_NLGRP_EVENT))
+		return;
+
+	msg_sz = __em_notify_pd_deleted_size(pd);
+
+	msg = genlmsg_new(msg_sz, GFP_KERNEL);
+	if (!msg)
+		return;
+
+	hdr = genlmsg_put(msg, 0, 0, &em_nl_family, 0, EM_CMD_PD_DELETED);
+	if (!hdr)
+		goto out_free_msg;
+
+	if (nla_put_u32(msg, EM_A_PD_TABLE_PD_ID, pd->id)) {
+		goto out_free_msg;
+	}
+
+	genlmsg_end(msg, hdr);
+
+	genlmsg_multicast(&em_nl_family, msg, 0, EM_NLGRP_EVENT, GFP_KERNEL);
+
+	return;
+
+out_free_msg:
+	nlmsg_free(msg);
+	return;
+}
+
+/**************************** Initialization *********************************/
 static int __init em_netlink_init(void)
 {
 	return genl_register_family(&em_nl_family);

kernel/power/em_netlink.h

@@ -13,6 +13,7 @@
 int for_each_em_perf_domain(int (*cb)(struct em_perf_domain*, void *),
 			    void *data);
 struct em_perf_domain *em_perf_domain_get_by_id(int id);
+void em_notify_pd_deleted(const struct em_perf_domain *pd);
 #else
 static inline
 int for_each_em_perf_domain(int (*cb)(struct em_perf_domain*, void *),
@@ -25,6 +26,8 @@ struct em_perf_domain *em_perf_domain_get_by_id(int id)
 {
 	return NULL;
 }
+
+static inline void em_notify_pd_deleted(const struct em_perf_domain *pd) {}
 #endif
 
 #endif /* _EM_NETLINK_H */