netdev - [PATCH net v2 1/2] net: fec: Set mac_managed

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Date: Thu, 29 Feb 2024 10:53:15 +0000
From: John Ernberg <john.ernberg@...ia.se>
To: Wei Fang <wei.fang@....com>
CC: Shenwei Wang <shenwei.wang@....com>, Clark Wang <xiaoning.wang@....com>,
	NXP Linux Team <linux-imx@....com>, "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, "Paolo
 Abeni" <pabeni@...hat.com>, Heiner Kallweit <hkallweit1@...il.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, John Ernberg
	<john.ernberg@...ia.se>
Subject: [PATCH net v2 1/2] net: fec: Set mac_managed_pm during probe

From: Wei Fang <wei.fang@....com>

Setting mac_managed_pm during interface up is too late.

In situations where the link is not brought up yet and the system suspends
the regular PHY power management will run. Since the FEC ETHEREN control
bit is cleared (automatically) on suspend the controller is off in resume.
When the regular PHY power management resume path runs in this context it
will write to the MII_DATA register but nothing will be transmitted on the
MDIO bus.

This can be observed by the following log:

    fec 5b040000.ethernet eth0: MDIO read timeout
    Microchip LAN87xx T1 5b040000.ethernet-1:04: PM: dpm_run_callback(): mdio_bus_phy_resume+0x0/0xc8 returns -110
    Microchip LAN87xx T1 5b040000.ethernet-1:04: PM: failed to resume: error -110

The data written will however remain in the MII_DATA register.

When the link later is brought up it will trigger a call to fec_restart()
which will restore the MII_SPEED register. This triggers the quirk
explained in f166f890c8f0 ("net: ethernet: fec: Replace interrupt driven
MDIO with polled IO") causing a MII_EVENT storm.

This event storm causes all the MDIO register reads to read as 0 because
fec_enet_mdio_wait() returns too early.

When a Microchip LAN8700R PHY is connected to the FEC, the 0 reads causes
the PHY to be initialized incorrectly and the PHY will not transmit any
ethernet signal in this state. It cannot be brought out of this state
without a power cycle of the PHY.

Fixes: 557d5dc83f68 ("net: fec: use mac-managed PHY PM")
Closes: https://lore.kernel.org/netdev/1f45bdbe-eab1-4e59-8f24-add177590d27@actia.se/
Signed-off-by: Wei Fang <wei.fang@....com>
[jernberg: commit message]
Signed-off-by: John Ernberg <john.ernberg@...ia.se>
---

v2: New patch. Big thanks to Wei for the help on this issue.
---
 drivers/net/ethernet/freescale/fec_main.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/freescale/fec_main.c b/drivers/net/ethernet/freescale/fec_main.c
index 432523b2c789..8decb1b072c5 100644
--- a/drivers/net/ethernet/freescale/fec_main.c
+++ b/drivers/net/ethernet/freescale/fec_main.c
@@ -2406,8 +2406,6 @@ static int fec_enet_mii_probe(struct net_device *ndev)
 	fep->link = 0;
 	fep->full_duplex = 0;

-	phy_dev->mac_managed_pm = true;
-
 	phy_attached_info(phy_dev);

 	return 0;
@@ -2419,10 +2417,12 @@ static int fec_enet_mii_init(struct platform_device *pdev)
 	struct net_device *ndev = platform_get_drvdata(pdev);
 	struct fec_enet_private *fep = netdev_priv(ndev);
 	bool suppress_preamble = false;
+	struct phy_device *phydev;
 	struct device_node *node;
 	int err = -ENXIO;
 	u32 mii_speed, holdtime;
 	u32 bus_freq;
+	int addr;

 	/*
 	 * The i.MX28 dual fec interfaces are not equal.
@@ -2536,6 +2536,13 @@ static int fec_enet_mii_init(struct platform_device *pdev)
 		goto err_out_free_mdiobus;
 	of_node_put(node);

+	/* find all the PHY devices on the bus and set mac_managed_pm to true */
+	for (addr = 0; addr < PHY_MAX_ADDR; addr++) {
+		phydev = mdiobus_get_phy(fep->mii_bus, addr);
+		if (phydev)
+			phydev->mac_managed_pm = true;
+	}
+
 	mii_cnt++;

 	/* save fec0 mii_bus */
-- 
2.43.0