[PATCH 7/7] net: phy: at803x: disable extended next page bit

[Marco Felsch <m.felsch@pengutronix.de>]

This commit ports Linux commit:

| commit 3c51fa5d2afe7a4909b53af5019635326389dd29
| Author: Russell King <rmk+kernel@armlinux.org.uk>
| Date:   Tue Jan 12 22:59:43 2021 +0000
|
|     net: phy: ar803x: disable extended next page bit
|
|     This bit is enabled by default and advertises support for extended
|     next page support.  XNP is only needed for 10GBase-T and MultiGig
|     support which is not supported. Additionally, Cisco MultiGig switches
|     will read this bit and attempt 10Gb negotiation even though Next Page
|     support is disabled. This will cause timeouts when the interface is
|     forced to 100Mbps and auto-negotiation will fail. The interfaces are
|     only 1000Base-T and supporting auto-negotiation for this only requires
|     the Next Page bit to be set.
|
|     Taken from:
|     https://github.com/SolidRun/linux-stable/commit/7406c5244b7ea6bc17a2afe8568277a8c4b126a9
|     and adapted to mainline kernels by rmk.
|
|     Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
|     Reviewed-by: Andrew Lunn <andrew@lunn.ch>
|     Link: https://lore.kernel.org/r/E1kzSdb-000417-FJ@rmk-PC.armlinux.org.uk
|     Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
---
 drivers/net/phy/at803x.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/net/phy/at803x.c b/drivers/net/phy/at803x.c
index d8a9c3588f..577bdf1244 100644
--- a/drivers/net/phy/at803x.c
+++ b/drivers/net/phy/at803x.c
@@ -365,7 +365,13 @@ static int at803x_config_init(struct phy_device *phydev)
 	if (ret < 0)
 		return ret;
 
-	return 0;
+	/* Ar803x extended next page bit is enabled by default. Cisco
+	 * multigig switches read this bit and attempt to negotiate 10Gbps
+	 * rates even if the next page bit is disabled. This is incorrect
+	 * behaviour but we still need to accommodate it. XNP is only needed
+	 * for 10Gbps support, so disable XNP.
+	 */
+	return phy_modify(phydev, MII_ADVERTISE, MDIO_AN_CTRL1_XNP, 0);
 }
 
 static struct phy_driver at803x_driver[] = {
-- 
2.39.2