PM: EM: Implement em_nl_get_pds_doit()

When a userspace requests EM_CMD_GET_PDS, the kernel responds with
information on all performance domains. The message format of the
response is as follows:

EM_A_PDS_PD (NLA_NESTED)*
    EM_A_PD_PD_ID (NLA_U32)
    EM_A_PD_FLAGS (NLA_U64)
    EM_A_PD_CPUS (NLA_STRING)

where EM_A_PDS_PD can be repeated as many times as there are performance
domains, and EM_A_PD_CPUS is a hexadecimal string representing a CPU
bitmask.

Signed-off-by: Changwoo Min <changwoo@igalia.com>
Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>
Link: https://patch.msgid.link/20251020220914.320832-7-changwoo@igalia.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Author: multics69

kernel/power/em_netlink.c

@@ -17,9 +17,89 @@
 #include "em_netlink.h"
 #include "em_netlink_autogen.h"
 
+#define EM_A_PD_CPUS_LEN		256
+
+/*************************** Command encoding ********************************/
+static int __em_nl_get_pd_size(struct em_perf_domain *pd, void *data)
+{
+	char cpus_buf[EM_A_PD_CPUS_LEN];
+	int *tot_msg_sz = data;
+	int msg_sz, cpus_sz;
+
+	cpus_sz = snprintf(cpus_buf, sizeof(cpus_buf), "%*pb",
+			   cpumask_pr_args(to_cpumask(pd->cpus)));
+
+	msg_sz = nla_total_size(0) +			/* EM_A_PDS_PD */
+		 nla_total_size(sizeof(u32)) +		/* EM_A_PD_PD_ID */
+		 nla_total_size_64bit(sizeof(u64)) +	/* EM_A_PD_FLAGS */
+		 nla_total_size(cpus_sz);		/* EM_A_PD_CPUS */
+
+	*tot_msg_sz += nlmsg_total_size(genlmsg_msg_size(msg_sz));
+	return 0;
+}
+
+static int __em_nl_get_pd(struct em_perf_domain *pd, void *data)
+{
+	char cpus_buf[EM_A_PD_CPUS_LEN];
+	struct sk_buff *msg = data;
+	struct nlattr *entry;
+
+	entry = nla_nest_start(msg, EM_A_PDS_PD);
+	if (!entry)
+		goto out_cancel_nest;
+
+	if (nla_put_u32(msg, EM_A_PD_PD_ID, pd->id))
+		goto out_cancel_nest;
+
+	if (nla_put_u64_64bit(msg, EM_A_PD_FLAGS, pd->flags, EM_A_PD_PAD))
+		goto out_cancel_nest;
+
+	snprintf(cpus_buf, sizeof(cpus_buf), "%*pb",
+		 cpumask_pr_args(to_cpumask(pd->cpus)));
+	if (nla_put_string(msg, EM_A_PD_CPUS, cpus_buf))
+		goto out_cancel_nest;
+
+	nla_nest_end(msg, entry);
+
+	return 0;
+
+out_cancel_nest:
+	nla_nest_cancel(msg, entry);
+
+	return -EMSGSIZE;
+}
+
 int em_nl_get_pds_doit(struct sk_buff *skb, struct genl_info *info)
 {
-	return -EOPNOTSUPP;
+	struct sk_buff *msg;
+	void *hdr;
+	int cmd = info->genlhdr->cmd;
+	int ret = -EMSGSIZE, msg_sz = 0;
+
+	for_each_em_perf_domain(__em_nl_get_pd_size, &msg_sz);
+
+	msg = genlmsg_new(msg_sz, GFP_KERNEL);
+	if (!msg)
+		return -ENOMEM;
+
+	hdr = genlmsg_put_reply(msg, info, &em_nl_family, 0, cmd);
+	if (!hdr)
+		goto out_free_msg;
+
+	ret = for_each_em_perf_domain(__em_nl_get_pd, msg);
+	if (ret)
+		goto out_cancel_msg;
+
+	genlmsg_end(msg, hdr);
+
+	return genlmsg_reply(msg, info);
+
+out_cancel_msg:
+	genlmsg_cancel(msg, hdr);
+out_free_msg:
+	nlmsg_free(msg);
+
+	return ret;
 }
 
 int em_nl_get_pd_table_doit(struct sk_buff *skb, struct genl_info *info)