netdev - Re: [PATCH net v1] net: dsa: mv88e6xxx: Make unsupported C45 reads return 0xffff

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Date: Tue, 23 Jan 2024 00:01:47 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Tim Menninger <tmenninger@...estorage.com>
Cc: Vladimir Oltean <vladimir.oltean@....com>,
	netdev-maintainers <edumazet@...gle.com>, kuba@...nel.org,
	pabeni@...hat.com, davem@...emloft.net,
	netdev <netdev@...r.kernel.org>, stable@...r.kernel.org
Subject: Re: [PATCH net v1] net: dsa: mv88e6xxx: Make unsupported C45 reads
 return 0xffff

> I'm not sure I fully agree with returning 0xffff here, and especially not
> for just one of the four functions (reads and writes, c22 and c45). If the
> end goal is to unify error handling, what if we keep the return values as
> they are, i.e. continue to return -EOPNOTSUPP, and then in get_phy_c22_id
> and get_phy_c45_ids on error we do something like:
> 
>     return (phy_reg == -EIO || phy_reg == -ENODEV || phy_reg == -EOPNOTSUPP)
>         ? -ENODEV : -EIO;

As i said to Vladimir, what i posted so far is just a minimal fix for
stable. After that, i have two patches for net-next, which are the
full, clean fix. And the first patch is similar to what you suggest:

+++ b/drivers/net/phy/phy_device.c
@@ -780,7 +780,7 @@ static int get_phy_c45_devs_in_pkg(struct mii_bus *bus, int addr, int dev_addr,
  * and identifiers in @c45_ids.
  *
  * Returns zero on success, %-EIO on bus access error, or %-ENODEV if
- * the "devices in package" is invalid.
+ * the "devices in package" is invalid or no device responds.
  */
 static int get_phy_c45_ids(struct mii_bus *bus, int addr,
                           struct phy_c45_device_ids *c45_ids)
@@ -803,7 +803,10 @@ static int get_phy_c45_ids(struct mii_bus *bus, int addr,
                         */
                        ret = phy_c45_probe_present(bus, addr, i);
                        if (ret < 0)
-                               return -EIO;
+                               /* returning -ENODEV doesn't stop bus
+                                * scanning */
+                               return (phy_reg == -EIO ||
+                                       phy_reg == -ENODEV) ? -ENODEV : -EIO;
 
                        if (!ret)
                                continue;

This makes C22 and C45 handling of -ENODEV the same.

I then have another patch which changed mv88e6xxx to return -ENODEV.
I cannot post the net-next patches for merging until the net patch is
accepted and then merged into net-next.

  Andrew