RDMA/core: Add hash functions to calculate RoCEv2 flowlabel and UDP source port

Add two hash functions to distribute RoCE v2 UDP source and Flowlabel
symmetrically. These are user visible API and any change in the
implementation needs to be tested for inter-operability between old and
new variant.

Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Mark Zhang <[e-mail]>
Reviewed-by: Maor Gottlieb <[e-mail]>
Signed-off-by: Leon Romanovsky <[e-mail]>
Signed-off-by: Jason Gunthorpe <[e-mail]>

include/rdma/ib_verbs.h

···
 
 bool rdma_dev_access_netns(const struct ib_device *device,
 			   const struct net *net);
+
+#define IB_ROCE_UDP_ENCAP_VALID_PORT_MIN (0xC000)
+#define IB_GRH_FLOWLABEL_MASK (0x000FFFFF)
+
+/**
+ * rdma_flow_label_to_udp_sport - generate a RoCE v2 UDP src port value based
+ *                               on the flow_label
+ *
+ * This function will convert the 20 bit flow_label input to a valid RoCE v2
+ * UDP src port 14 bit value. All RoCE V2 drivers should use this same
+ * convention.
+ */
+static inline u16 rdma_flow_label_to_udp_sport(u32 fl)
+{
+	u32 fl_low = fl & 0x03fff, fl_high = fl & 0xFC000;
+
+	fl_low ^= fl_high >> 14;
+	return (u16)(fl_low | IB_ROCE_UDP_ENCAP_VALID_PORT_MIN);
+}
+
+/**
+ * rdma_calc_flow_label - generate a RDMA symmetric flow label value based on
+ *                        local and remote qpn values
+ *
+ * This function folded the multiplication results of two qpns, 24 bit each,
+ * fields, and converts it to a 20 bit results.
+ *
+ * This function will create symmetric flow_label value based on the local
+ * and remote qpn values. this will allow both the requester and responder
+ * to calculate the same flow_label for a given connection.
+ *
+ * This helper function should be used by driver in case the upper layer
+ * provide a zero flow_label value. This is to improve entropy of RDMA
+ * traffic in the network.
+ */
+static inline u32 rdma_calc_flow_label(u32 lqpn, u32 rqpn)
+{
+	u64 v = (u64)lqpn * rqpn;
+
+	v ^= v >> 20;
+	v ^= v >> 40;
+
+	return (u32)(v & IB_GRH_FLOWLABEL_MASK);
+}
 #endif /* IB_VERBS_H */