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Subject[PATCH v3 04/10] NTB: Introduce functions to calculate multi-port resource index
When using multi-ports each port uses resources (dbs, msgs, mws, etc)
on every other port. Creating a mapping for these resources such that
each port has a corresponding resource on every other port is a bit
tricky.

Introduce the ntb_peer_resource_idx() function for this purpose.
It returns the peer resource number that will correspond with the
local peer index on the remote peer.

Also, introduce ntb_peer_highest_mw_idx() which will use
ntb_peer_resource_idx() but return the MW index starting with the
highest index and working down.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Cc: Jon Mason <jdmason@kudzu.us>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Allen Hubbe <allenbh@gmail.com>
---
include/linux/ntb.h | 70 +++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 70 insertions(+)

diff --git a/include/linux/ntb.h b/include/linux/ntb.h
index 52060b2130b6..a14a43b17952 100644
--- a/include/linux/ntb.h
+++ b/include/linux/ntb.h
@@ -1557,4 +1557,74 @@ static inline int ntb_peer_msg_write(struct ntb_dev *ntb, int pidx, int midx,
return ntb->ops->peer_msg_write(ntb, pidx, midx, msg);
}

+/**
+ * ntb_peer_resource_idx() - get a resource index for a given peer idx
+ * @ntb: NTB device context.
+ * @pidx: Peer port index.
+ *
+ * When constructing a graph of peers, each remote peer must use a different
+ * resource index (mw, doorbell, etc) to communicate with each other
+ * peer.
+ *
+ * In a two peer system, this function should always return 0 such that
+ * resource 0 points to the remote peer on both ports.
+ *
+ * In a 5 peer system, this function will return the following matrix
+ *
+ * pidx \ port 0 1 2 3 4
+ * 0 0 0 1 2 3
+ * 1 0 1 1 2 3
+ * 2 0 1 2 2 3
+ * 3 0 1 2 3 3
+ *
+ * For example, if this function is used to program peer's memory
+ * windows, port 0 will program MW 0 on all it's peers to point to itself.
+ * port 1 will program MW 0 in port 0 to point to itself and MW 1 on all
+ * other ports. etc.
+ *
+ * For the legacy two host case, ntb_port_number() and ntb_peer_port_number()
+ * both return zero and therefore this function will always return zero.
+ * So MW 0 on each host would be programmed to point to the other host.
+ *
+ * Return: the resource index to use for that peer.
+ */
+static inline int ntb_peer_resource_idx(struct ntb_dev *ntb, int pidx)
+{
+ int local_port, peer_port;
+
+ if (pidx >= ntb_peer_port_count(ntb))
+ return -EINVAL;
+
+ local_port = ntb_logical_port_number(ntb);
+ peer_port = ntb_peer_logical_port_number(ntb, pidx);
+
+ if (peer_port < local_port)
+ return local_port - 1;
+ else
+ return local_port;
+}
+
+/**
+ * ntb_peer_highest_mw_idx() - get a memory window index for a given peer idx
+ * using the highest index memory windows first
+ *
+ * @ntb: NTB device context.
+ * @pidx: Peer port index.
+ *
+ * Like ntb_peer_resource_idx(), except it returns indexes starting with
+ * last memory window index.
+ *
+ * Return: the resource index to use for that peer.
+ */
+static inline int ntb_peer_highest_mw_idx(struct ntb_dev *ntb, int pidx)
+{
+ int ret;
+
+ ret = ntb_peer_resource_idx(ntb, pidx);
+ if (ret < 0)
+ return ret;
+
+ return ntb_mw_count(ntb, pidx) - ret - 1;
+}
+
#endif
--
2.20.1
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