nfp: devlink port split support for 1x100G CXP NIC

[ Upstream commit 5948185b97fa1f83d7855e638a72982a1073ebf5 ]

This commit makes it possible to use devlink to split the 100G CXP
Netronome into two 40G interfaces. Currently when you ask for 2
interfaces, the math in src/nfp_devlink.c:nfp_devlink_port_split
calculates that you want 5 lanes per port because for some reason
eth_port.port_lanes=10 (shouldn't this be 12 for CXP?). What we really
want when asking for 2 breakout interfaces is 4 lanes per port. This
commit makes that happen by calculating based on 8 lanes if 10 are
present.

Signed-off-by: Ryan C Goodfellow <rgoodfel@isi.edu>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Greg Weeks <greg.weeks@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/net/ethernet/netronome/nfp/nfp_devlink.c

@@ -96,6 +96,7 @@ nfp_devlink_port_split(struct devlink *devlink, unsigned int port_index,
 {
 	struct nfp_pf *pf = devlink_priv(devlink);
 	struct nfp_eth_table_port eth_port;
+	unsigned int lanes;
 	int ret;
 
 	if (count < 2)
@@ -114,8 +115,12 @@ nfp_devlink_port_split(struct devlink *devlink, unsigned int port_index,
 		goto out;
 	}
 
-	ret = nfp_devlink_set_lanes(pf, eth_port.index,
-				    eth_port.port_lanes / count);
+	/* Special case the 100G CXP -> 2x40G split */
+	lanes = eth_port.port_lanes / count;
+	if (eth_port.lanes == 10 && count == 2)
+		lanes = 8 / count;
+
+	ret = nfp_devlink_set_lanes(pf, eth_port.index, lanes);
 out:
 	mutex_unlock(&pf->lock);
 
@@ -128,6 +133,7 @@ nfp_devlink_port_unsplit(struct devlink *devlink, unsigned int port_index,
 {
 	struct nfp_pf *pf = devlink_priv(devlink);
 	struct nfp_eth_table_port eth_port;
+	unsigned int lanes;
 	int ret;
 
 	mutex_lock(&pf->lock);
@@ -143,7 +149,12 @@ nfp_devlink_port_unsplit(struct devlink *devlink, unsigned int port_index,
 		goto out;
 	}
 
-	ret = nfp_devlink_set_lanes(pf, eth_port.index, eth_port.port_lanes);
+	/* Special case the 100G CXP -> 2x40G unsplit */
+	lanes = eth_port.port_lanes;
+	if (eth_port.port_lanes == 8)
+		lanes = 10;
+
+	ret = nfp_devlink_set_lanes(pf, eth_port.index, lanes);
 out:
 	mutex_unlock(&pf->lock);