[PATCH net v2] net: marvell: prestera: disable port before changing its MAC mode

[Imre Kaloz <kaloz@kernel.org>]

prestera_pcs_config() writes a new mode, speed or inband setting to an
enabled port. The firmware can then report link down until the port is
disabled and enabled again.

Disable the port before such a write. 2500BASE-X and SGMII share one MAC
mode, so SGMII sets its own speed and the speed is compared as well.
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>
---
Changes in v2:
- Also disable the port on a speed change and set the SGMII speed, so
  that a switch between 2500BASE-X and SGMII, which share one MAC mode,
  is covered.
- Elad's Reviewed-by from v1 is not carried over, given the changes to the logic.
- Link to v1: https://lore.kernel.org/netdev/20261111101521.9878-1-kaloz@kernel.org/

 .../ethernet/marvell/prestera/prestera_main.c   | 17 ++++++++++++++++-
 1 file changed, 16 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..3173145573600 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;
@@ -329,6 +330,7 @@ static int prestera_pcs_config(struct phylink_pcs *pcs, unsigned int neg_mode,
 		cfg_mac.mode = PRESTERA_MAC_MODE_SGMII;
 		break;
 	case PHY_INTERFACE_MODE_SGMII:
+		cfg_mac.speed = SPEED_1000;
 		cfg_mac.mode = PRESTERA_MAC_MODE_SGMII;
 		break;
 	case PHY_INTERFACE_MODE_1000BASEX:
@@ -339,6 +341,19 @@ static int prestera_pcs_config(struct phylink_pcs *pcs, unsigned int neg_mode,
 		break;
 	}
 
+	/* Firmware may not report link up after the mode, speed 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.speed != cfg_mac.speed ||
+			  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