linux-kernel - [PATCH v4 1/1] net: fec: Set mac_managed

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Date: Thu, 28 Mar 2024 15:59:29 +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>,
	"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>, "imx@...ts.linux.dev"
	<imx@...ts.linux.dev>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "Florian
 Fainelli" <f.fainelli@...il.com>, Russell King <linux@...linux.org.uk>,
	"Maxime Chevallier" <maxime.chevallier@...tlin.com>, John Ernberg
	<john.ernberg@...ia.se>
Subject: [PATCH v4 1/1] 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 set to administrative 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 an extra MII_EVENT.

This extra event desynchronizes all the MDIO register reads, causing them
to complete too early. Leading all 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>

---

v4:
 - Adjustments to commit message after a better understanding of the
   behavior explained in f166f890c8f0 as a result of the discussion on v3
   patch 2.

v3:
 - No changes

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 d7693fdf640d..8bd213da8fb6 100644
--- a/drivers/net/ethernet/freescale/fec_main.c
+++ b/drivers/net/ethernet/freescale/fec_main.c
@@ -2454,8 +2454,6 @@ 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;
@@ -2467,10 +2465,12 @@ 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.
@@ -2584,6 +2584,13 @@ 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 */
-- 
2.44.0