linux-kernel - [PATCH net 2/2] net: phy: Check harder for errors in get_phy

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Message-Id: <20200619044759.11387-3-f.fainelli@gmail.com>
Date:   Thu, 18 Jun 2020 21:47:59 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     netdev@...r.kernel.org
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Dajun Jin <adajunjin@...il.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        linux-kernel@...r.kernel.org (open list),
        devicetree@...r.kernel.org (open list:OPEN FIRMWARE AND FLATTENED
        DEVICE TREE)
Subject: [PATCH net 2/2] net: phy: Check harder for errors in get_phy_id()

Commit 02a6efcab675 ("net: phy: allow scanning busses with missing
phys") added a special condition to return -ENODEV in case -ENODEV or
-EIO was returned from the first read of the MII_PHYSID1 register.

In case the MDIO bus data line pull-up is not strong enough, the MDIO
bus controller will not flag this as a read error. This can happen when
a pluggable daughter card is not connected and weak internal pull-ups
are used (since that is the only option, otherwise the pins are
floating).

The second read of MII_PHYSID2 will be correctly flagged an error
though, but now we will return -EIO which will be treated as a hard
error, thus preventing MDIO bus scanning loops to continue succesfully.

Apply the same logic to both register reads, thus allowing the scanning
logic to proceed.

Fixes: 02a6efcab675 ("net: phy: allow scanning busses with missing phys")
Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
---
 drivers/net/phy/phy_device.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
index 04946de74fa0..85ba95b598b5 100644
--- a/drivers/net/phy/phy_device.c
+++ b/drivers/net/phy/phy_device.c
@@ -794,8 +794,10 @@ static int get_phy_id(struct mii_bus *bus, int addr, u32 *phy_id,
 
 	/* Grab the bits from PHYIR2, and put them in the lower half */
 	phy_reg = mdiobus_read(bus, addr, MII_PHYSID2);
-	if (phy_reg < 0)
-		return -EIO;
+	if (phy_reg < 0) {
+		/* returning -ENODEV doesn't stop bus scanning */
+		return (phy_reg == -EIO || phy_reg == -ENODEV) ? -ENODEV : -EIO;
+	}
 
 	*phy_id |= phy_reg;
 
-- 
2.17.1