RDMA: Lift ibdev_to_node from rds to common code

Lift the ibdev_to_node from rds to common code and document it.

Link: https://lore.kernel.org/r/20201106181941.1878556-4-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

include/rdma/ib_verbs.h

@@ -4549,6 +4549,19 @@ static inline struct ib_device *rdma_device_to_ibdev(struct device *device)
 	return coredev->owner;
 }
 
+/**
+ * ibdev_to_node - return the NUMA node for a given ib_device
+ * @dev:	device to get the NUMA node for.
+ */
+static inline int ibdev_to_node(struct ib_device *ibdev)
+{
+	struct device *parent = ibdev->dev.parent;
+
+	if (!parent)
+		return NUMA_NO_NODE;
+	return dev_to_node(parent);
+}
+
 /**
  * rdma_device_to_drv_device - Helper macro to reach back to driver's
  *			       ib_device holder structure from device pointer.

net/rds/ib.h

@@ -264,13 +264,6 @@ struct rds_ib_device {
 	int			*vector_load;
 };
 
-static inline int ibdev_to_node(struct ib_device *ibdev)
-{
-	struct device *parent;
-
-	parent = ibdev->dev.parent;
-	return parent ? dev_to_node(parent) : NUMA_NO_NODE;
-}
 #define rdsibdev_to_node(rdsibdev) ibdev_to_node(rdsibdev->dev)
 
 /* bits for i_ack_flags */