[PATCH net] net: marvell: prestera: disable port before changing its MAC mode

[Imre Kaloz <kaloz@kernel.org>]

prestera_pcs_config() writes a new mode or inband setting to a port
that is already enabled, as when phylink switches an SFP port to
inband SGMII. The firmware can then report link down and no link up
until the port is disabled and enabled again.

Disable the port before such a write. Exercising this needs a link
partner, so no in-tree test covers it.

Fixes: 52323ef75414 ("net: marvell: prestera: add phylink support")
Signed-off-by: Imre Kaloz <kaloz@kernel.org>
---
 .../net/ethernet/marvell/prestera/prestera_main.c  | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/marvell/prestera/prestera_main.c b/drivers/net/ethernet/marvell/prestera/prestera_main.c
index a82e7a8029851..39ebd1944be55 100644
--- a/drivers/net/ethernet/marvell/prestera/prestera_main.c
+++ b/drivers/net/ethernet/marvell/prestera/prestera_main.c
@@ -307,13 +307,14 @@ static int prestera_pcs_config(struct phylink_pcs *pcs, unsigned int neg_mode,
 			       bool permit_pause_to_mac)
 {
 	struct prestera_port *port = prestera_pcs_to_port(pcs);
-	struct prestera_port_mac_config cfg_mac;
+	struct prestera_port_mac_config cfg_mac, old;
 	int err;
 
 	err = prestera_port_cfg_mac_read(port, &cfg_mac);
 	if (err)
 		return err;
 
+	old = cfg_mac;
 	cfg_mac.admin = true;
 	cfg_mac.fec = PRESTERA_PORT_FEC_OFF;
 	cfg_mac.inband = neg_mode == PHYLINK_PCS_NEG_INBAND_ENABLED;
@@ -339,6 +340,17 @@ static int prestera_pcs_config(struct phylink_pcs *pcs, unsigned int neg_mode,
 		break;
 	}
 
+	/* Firmware may not report link up after the mode or inband setting of
+	 * an enabled port changes until the port is disabled and re-enabled.
+	 */
+	if (old.admin && (old.mode != cfg_mac.mode ||
+			  old.inband != cfg_mac.inband)) {
+		old.admin = false;
+		err = prestera_port_cfg_mac_write(port, &old);
+		if (err)
+			return err;
+	}
+
 	err = prestera_port_cfg_mac_write(port, &cfg_mac);
 	if (err)
 		return err;
-- 
2.47.3