[PATCH net v2 0/2] net: phy: MDIO bus scanning fixes

[PATCH net v2 0/2] net: phy: MDIO bus scanning fixes

[Florian Fainelli]

Hi all,

This patch series fixes two problems with the current MDIO bus scanning
logic which was identified while moving from 4.9 to 5.4 on devices that
do rely on scanning the MDIO bus at runtime because they use pluggable
cards.

Changes in v2:

- added comment explaining the special value of -ENODEV
- added Andrew's Reviewed-by tag

Florian Fainelli (2):
  of: of_mdio: Correct loop scanning logic
  net: phy: Check harder for errors in get_phy_id()

 drivers/net/phy/phy_device.c | 6 ++++--
 drivers/of/of_mdio.c         | 9 +++++++--
 2 files changed, 11 insertions(+), 4 deletions(-)

-- 
2.17.1

[PATCH net v2 1/2] of: of_mdio: Correct loop scanning logic

[Florian Fainelli]

Commit 209c65b61d94 ("drivers/of/of_mdio.c:fix of_mdiobus_register()")
introduced a break of the loop on the premise that a successful
registration should exit the loop. The premise is correct but not to
code, because rc && rc != -ENODEV is just a special error condition,
that means we would exit the loop even with rc == -ENODEV which is
absolutely not correct since this is the error code to indicate to the
MDIO bus layer that scanning should continue.

Fix this by explicitly checking for rc = 0 as the only valid condition
to break out of the loop.

Fixes: 209c65b61d94 ("drivers/of/of_mdio.c:fix of_mdiobus_register()")
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
---
 drivers/of/of_mdio.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/of/of_mdio.c b/drivers/of/of_mdio.c
index a04afe79529c..ef6f818ce5b3 100644
--- a/drivers/of/of_mdio.c
+++ b/drivers/of/of_mdio.c
@@ -314,10 +314,15 @@ int of_mdiobus_register(struct mii_bus *mdio, struct device_node *np)
 				 child, addr);
 
 			if (of_mdiobus_child_is_phy(child)) {
+				/* -ENODEV is the return code that PHYLIB has
+				 * standardized on to indicate that bus
+				 * scanning should continue.
+				 */
 				rc = of_mdiobus_register_phy(mdio, child, addr);
-				if (rc && rc != -ENODEV)
+				if (!rc)
+					break;
+				if (rc != -ENODEV)
 					goto unregister;
-				break;
 			}
 		}
 	}
-- 
2.17.1

[PATCH net v2 2/2] net: phy: Check harder for errors in get_phy_id()

[Florian Fainelli]

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")
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.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

Re: [PATCH net v2 0/2] net: phy: MDIO bus scanning fixes

[David Miller]

From: Florian Fainelli <f.fainelli@gmail.com>
Date: Fri, 19 Jun 2020 11:47:45 -0700

> This patch series fixes two problems with the current MDIO bus scanning
> logic which was identified while moving from 4.9 to 5.4 on devices that
> do rely on scanning the MDIO bus at runtime because they use pluggable
> cards.
> 
> Changes in v2:
> 
> - added comment explaining the special value of -ENODEV
> - added Andrew's Reviewed-by tag

Series applied and queued up for -stable, thanks.