RDMA/core: Do not expose unsupported counters

If the provider driver (such as rdma_rxe) doesn't support pma counters,
avoid exposing its directory similar to optional hw_counters directory.
If core fails to read the PMA counter, return an error so that user can
retry later if needed.

Fixes: 35c4cbb1 ("IB/core: Create get_perf_mad function in sysfs.c")
Reported-by: Holger Hoffstätte <holger@applied-asynchrony.com>
Tested-by: Holger Hoffstätte <holger@applied-asynchrony.com>
Signed-off-by: Parav Pandit <parav@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/core/sysfs.c

@@ -512,7 +512,7 @@ static ssize_t show_pma_counter(struct ib_port *p, struct port_attribute *attr,
 	ret = get_perf_mad(p->ibdev, p->port_num, tab_attr->attr_id, &data,
 			40 + offset / 8, sizeof(data));
 	if (ret < 0)
-		return sprintf(buf, "N/A (no PMA)\n");
+		return ret;
 
 	switch (width) {
 	case 4:
@@ -1057,10 +1057,12 @@ static int add_port(struct ib_device *device, int port_num,
 		goto err_put;
 	}
 
-	p->pma_table = get_counter_table(device, port_num);
-	ret = sysfs_create_group(&p->kobj, p->pma_table);
-	if (ret)
-		goto err_put_gid_attrs;
+	if (device->process_mad) {
+		p->pma_table = get_counter_table(device, port_num);
+		ret = sysfs_create_group(&p->kobj, p->pma_table);
+		if (ret)
+			goto err_put_gid_attrs;
+	}
 
 	p->gid_group.name  = "gids";
 	p->gid_group.attrs = alloc_group_attrs(show_port_gid, attr.gid_tbl_len);
@@ -1173,7 +1175,8 @@ static int add_port(struct ib_device *device, int port_num,
 	p->gid_group.attrs = NULL;
 
 err_remove_pma:
-	sysfs_remove_group(&p->kobj, p->pma_table);
+	if (p->pma_table)
+		sysfs_remove_group(&p->kobj, p->pma_table);
 
 err_put_gid_attrs:
 	kobject_put(&p->gid_attr_group->kobj);
@@ -1289,7 +1292,9 @@ static void free_port_list_attributes(struct ib_device *device)
 			kfree(port->hw_stats);
 			free_hsag(&port->kobj, port->hw_stats_ag);
 		}
-		sysfs_remove_group(p, port->pma_table);
+
+		if (port->pma_table)
+			sysfs_remove_group(p, port->pma_table);
 		sysfs_remove_group(p, &port->pkey_group);
 		sysfs_remove_group(p, &port->gid_group);
 		sysfs_remove_group(&port->gid_attr_group->kobj,