netdev - [PATCH net] net: phy: ensure PHY is powered up when reading ID registers

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Message-ID: <68d8022b-493a-1c9a-72c2-2f16df835fab@gmail.com>
Date:   Sat, 5 Jan 2019 14:21:03 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        David Miller <davem@...emloft.net>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: [PATCH net] net: phy: ensure PHY is powered up when reading ID
 registers

During a bug analysis we came across the fact that there's no guarantee
that reading from the ID registers returns a valid value if PHY is
powered down. When reading invalid values we may load no or the wrong
PHY driver. Therefore let's play safe and power up the PHY before
reading the ID registers in case PHY is powered down.

Suggested-by: Florian Fainelli <f.fainelli@...il.com>
Signed-off-by: Heiner Kallweit <hkallweit1@...il.com>
---
 drivers/net/phy/phy_device.c | 23 +++++++++++++----------
 1 file changed, 13 insertions(+), 10 deletions(-)

diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
index 9560a2b84..d4702313d 100644
--- a/drivers/net/phy/phy_device.c
+++ b/drivers/net/phy/phy_device.c
@@ -754,19 +754,22 @@ static int get_phy_id(struct mii_bus *bus, int addr, u32 *phy_id,
 	if (is_c45)
 		return get_phy_c45_ids(bus, addr, phy_id, c45_ids);
 
+	phy_reg = mdiobus_read(bus, addr, MII_BMCR);
+	if (phy_reg < 0)
+		/* returning -ENODEV allows to continue bus-scanning */
+		return (phy_reg == -EIO || phy_reg == -ENODEV) ? -ENODEV : -EIO;
+
+	/* PHY may be powered down and ID registers invalid */
+	if (phy_reg & BMCR_PDOWN) {
+		mdiobus_write(bus, addr, MII_BMCR, phy_reg & ~BMCR_PDOWN);
+		/* give the PHY some time to resume */
+		msleep(100);
+	}
+
 	/* Grab the bits from PHYIR1, and put them in the upper half */
 	phy_reg = mdiobus_read(bus, addr, MII_PHYSID1);
-	if (phy_reg < 0) {
-		/* if there is no device, return without an error so scanning
-		 * the bus works properly
-		 */
-		if (phy_reg == -EIO || phy_reg == -ENODEV) {
-			*phy_id = 0xffffffff;
-			return 0;
-		}
-
+	if (phy_reg < 0)
 		return -EIO;
-	}
 
 	*phy_id = (phy_reg & 0xffff) << 16;
 
-- 
2.20.1