Formally register smc as dibs client. Functionality will be moved by
follow-on patches from ism_client to dibs_client until eventually
ism_client can be removed.
As DIBS is only a shim layer without any dependencies, we can depend SMC
on DIBS without adding indirect dependencies. A follow-on patch will
remove dependency of SMC on ISM.

Signed-off-by: Alexandra Winter <wintera@linux.ibm.com>
Reviewed-by: Julian Ruess <julianr@linux.ibm.com>
---
 arch/s390/configs/debug_defconfig |  1 +
 arch/s390/configs/defconfig       |  1 +
 include/linux/dibs.h              | 24 ++++++++++++++++++++-
 net/dibs/dibs_main.c              | 35 +++++++++++++++++++++++++++++++
 net/smc/Kconfig                   |  2 +-
 net/smc/smc_ism.c                 |  6 ++++++
 6 files changed, 67 insertions(+), 2 deletions(-)

diff --git a/arch/s390/configs/debug_defconfig b/arch/s390/configs/debug_defconfig
index 5e616bc988ac..7bc54f053a3b 100644
--- a/arch/s390/configs/debug_defconfig
+++ b/arch/s390/configs/debug_defconfig
@@ -120,6 +120,7 @@ CONFIG_UNIX=y
 CONFIG_UNIX_DIAG=m
 CONFIG_XFRM_USER=m
 CONFIG_NET_KEY=m
+CONFIG_DIBS=y
 CONFIG_SMC_DIAG=m
 CONFIG_SMC_LO=y
 CONFIG_INET=y
diff --git a/arch/s390/configs/defconfig b/arch/s390/configs/defconfig
index 094599cdaf4d..4bf6f3311f7d 100644
--- a/arch/s390/configs/defconfig
+++ b/arch/s390/configs/defconfig
@@ -111,6 +111,7 @@ CONFIG_UNIX=y
 CONFIG_UNIX_DIAG=m
 CONFIG_XFRM_USER=m
 CONFIG_NET_KEY=m
+CONFIG_DIBS=y
 CONFIG_SMC_DIAG=m
 CONFIG_SMC_LO=y
 CONFIG_INET=y
diff --git a/include/linux/dibs.h b/include/linux/dibs.h
index 3f4175aaa732..5c432699becb 100644
--- a/include/linux/dibs.h
+++ b/include/linux/dibs.h
@@ -33,10 +33,32 @@
  * clients.
  */
 
+/* DIBS client
+ * -----------
+ */
 #define MAX_DIBS_CLIENTS	8
-
 struct dibs_client {
+	/* client name for logging and debugging purposes */
 	const char *name;
+	/* client index - provided and used by dibs layer */
+	u8 id;
 };
 
+/* Functions to be called by dibs clients:
+ */
+/**
+ * dibs_register_client() - register a client with dibs layer
+ * @client: this client
+ *
+ * Return: zero on success.
+ */
+int dibs_register_client(struct dibs_client *client);
+/**
+ * dibs_unregister_client() - unregister a client with dibs layer
+ * @client: this client
+ *
+ * Return: zero on success.
+ */
+int dibs_unregister_client(struct dibs_client *client);
+
 #endif	/* _DIBS_H */
diff --git a/net/dibs/dibs_main.c b/net/dibs/dibs_main.c
index 68e189932fcf..a5d2be9c3246 100644
--- a/net/dibs/dibs_main.c
+++ b/net/dibs/dibs_main.c
@@ -20,6 +20,41 @@ MODULE_LICENSE("GPL");
 /* use an array rather a list for fast mapping: */
 static struct dibs_client *clients[MAX_DIBS_CLIENTS];
 static u8 max_client;
+static DEFINE_MUTEX(clients_lock);
+
+int dibs_register_client(struct dibs_client *client)
+{
+	int i, rc = -ENOSPC;
+
+	mutex_lock(&clients_lock);
+	for (i = 0; i < MAX_DIBS_CLIENTS; ++i) {
+		if (!clients[i]) {
+			clients[i] = client;
+			client->id = i;
+			if (i == max_client)
+				max_client++;
+			rc = 0;
+			break;
+		}
+	}
+	mutex_unlock(&clients_lock);
+
+	return rc;
+}
+EXPORT_SYMBOL_GPL(dibs_register_client);
+
+int dibs_unregister_client(struct dibs_client *client)
+{
+	int rc = 0;
+
+	mutex_lock(&clients_lock);
+	clients[client->id] = NULL;
+	if (client->id + 1 == max_client)
+		max_client--;
+	mutex_unlock(&clients_lock);
+	return rc;
+}
+EXPORT_SYMBOL_GPL(dibs_unregister_client);
 
 static int __init dibs_init(void)
 {
diff --git a/net/smc/Kconfig b/net/smc/Kconfig
index ba5e6a2dd2fd..40dd60c1d23f 100644
--- a/net/smc/Kconfig
+++ b/net/smc/Kconfig
@@ -1,7 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0-only
 config SMC
 	tristate "SMC socket protocol family"
-	depends on INET && INFINIBAND
+	depends on INET && INFINIBAND && DIBS
 	depends on m || ISM != m
 	help
 	  SMC-R provides a "sockets over RDMA" solution making use of
diff --git a/net/smc/smc_ism.c b/net/smc/smc_ism.c
index 503a9f93b392..a7a965e3c0ce 100644
--- a/net/smc/smc_ism.c
+++ b/net/smc/smc_ism.c
@@ -18,6 +18,7 @@
 #include "smc_pnet.h"
 #include "smc_netlink.h"
 #include "linux/ism.h"
+#include "linux/dibs.h"
 
 struct smcd_dev_list smcd_dev_list = {
 	.list = LIST_HEAD_INIT(smcd_dev_list.list),
@@ -42,6 +43,9 @@ static struct ism_client smc_ism_client = {
 	.handle_irq = smcd_handle_irq,
 };
 #endif
+static struct dibs_client smc_dibs_client = {
+	.name = "SMC-D",
+};
 
 static void smc_ism_create_system_eid(void)
 {
@@ -623,11 +627,13 @@ int smc_ism_init(void)
 #if IS_ENABLED(CONFIG_ISM)
 	rc = ism_register_client(&smc_ism_client);
 #endif
+	rc = dibs_register_client(&smc_dibs_client);
 	return rc;
 }
 
 void smc_ism_exit(void)
 {
+	dibs_unregister_client(&smc_dibs_client);
 #if IS_ENABLED(CONFIG_ISM)
 	ism_unregister_client(&smc_ism_client);
 #endif
-- 
2.48.1