net: dsa: stop overriding master's ndo_get_phys_port_name

The purpose of this override is to give the user an indication of what
the number of the CPU port is (in DSA, the CPU port is a hardware
implementation detail and not a network interface capable of traffic).

However, it has always failed (by design) at providing this information
to the user in a reliable fashion.

Prior to commit 3369afba ("net: Call into DSA netdevice_ops
wrappers"), the behavior was to only override this callback if it was
not provided by the DSA master.

That was its first failure: if the DSA master itself was a DSA port or a
switchdev, then the user would not see the number of the CPU port in
/sys/class/net/eth0/phys_port_name, but the number of the DSA master
port within its respective physical switch.

But that was actually ok in a way. The commit mentioned above changed
that behavior, and now overrides the master's ndo_get_phys_port_name
unconditionally. That comes with problems of its own, which are worse in
a way.

The idea is that it's typical for switchdev users to have udev rules for
consistent interface naming. These are based, among other things, on
the phys_port_name attribute. If we let the DSA switch at the bottom
to start randomly overriding ndo_get_phys_port_name with its own CPU
port, we basically lose any predictability in interface naming, or even
uniqueness, for that matter.

So, there are reasons to let DSA override the master's callback (to
provide a consistent interface, a number which has a clear meaning and
must not be interpreted according to context), and there are reasons to
not let DSA override it (it breaks udev matching for the DSA master).

But, there is an alternative method for users to retrieve the number of
the CPU port of each DSA switch in the system:

  $ devlink port
  pci/0000:00:00.5/0: type eth netdev swp0 flavour physical port 0
  pci/0000:00:00.5/2: type eth netdev swp2 flavour physical port 2
  pci/0000:00:00.5/4: type notset flavour cpu port 4
  spi/spi2.0/0: type eth netdev sw0p0 flavour physical port 0
  spi/spi2.0/1: type eth netdev sw0p1 flavour physical port 1
  spi/spi2.0/2: type eth netdev sw0p2 flavour physical port 2
  spi/spi2.0/4: type notset flavour cpu port 4
  spi/spi2.1/0: type eth netdev sw1p0 flavour physical port 0
  spi/spi2.1/1: type eth netdev sw1p1 flavour physical port 1
  spi/spi2.1/2: type eth netdev sw1p2 flavour physical port 2
  spi/spi2.1/3: type eth netdev sw1p3 flavour physical port 3
  spi/spi2.1/4: type notset flavour cpu port 4

So remove this duplicated, unreliable and troublesome method. From this
patch on, the phys_port_name attribute of the DSA master will only
contain information about itself (if at all). If the users need reliable
information about the CPU port they're probably using devlink anyway.
Signed-off-by: Vladimir Oltean <olteanv@gmail.com>
Acked-by: florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/dsa.h

@@ -94,8 +94,6 @@ struct dsa_device_ops {
 struct dsa_netdevice_ops {
 	int (*ndo_do_ioctl)(struct net_device *dev, struct ifreq *ifr,
 			    int cmd);
-	int (*ndo_get_phys_port_name)(struct net_device *dev, char *name,
-				      size_t len);
 };
 
 #define DSA_TAG_DRIVER_ALIAS "dsa_tag-"
@@ -719,33 +717,12 @@ static inline int dsa_ndo_do_ioctl(struct net_device *dev, struct ifreq *ifr,
 
 	return ops->ndo_do_ioctl(dev, ifr, cmd);
 }
-
-static inline int dsa_ndo_get_phys_port_name(struct net_device *dev,
-					     char *name, size_t len)
-{
-	const struct dsa_netdevice_ops *ops;
-	int err;
-
-	err = __dsa_netdevice_ops_check(dev);
-	if (err)
-		return err;
-
-	ops = dev->dsa_ptr->netdev_ops;
-
-	return ops->ndo_get_phys_port_name(dev, name, len);
-}
 #else
 static inline int dsa_ndo_do_ioctl(struct net_device *dev, struct ifreq *ifr,
 				   int cmd)
 {
 	return -EOPNOTSUPP;
 }
-
-static inline int dsa_ndo_get_phys_port_name(struct net_device *dev,
-					     char *name, size_t len)
-{
-	return -EOPNOTSUPP;
-}
 #endif
 
 void dsa_unregister_switch(struct dsa_switch *ds);

net/core/dev.c

@@ -98,7 +98,6 @@
 #include <net/busy_poll.h>
 #include <linux/rtnetlink.h>
 #include <linux/stat.h>
-#include <net/dsa.h>
 #include <net/dst.h>
 #include <net/dst_metadata.h>
 #include <net/pkt_sched.h>
@@ -8605,10 +8604,6 @@ int dev_get_phys_port_name(struct net_device *dev,
 	const struct net_device_ops *ops = dev->netdev_ops;
 	int err;
 
-	err  = dsa_ndo_get_phys_port_name(dev, name, len);
-	if (err == 0 || err != -EOPNOTSUPP)
-		return err;
-
 	if (ops->ndo_get_phys_port_name) {
 		err = ops->ndo_get_phys_port_name(dev, name, len);
 		if (err != -EOPNOTSUPP)

net/dsa/master.c

@@ -186,17 +186,6 @@ static void dsa_master_get_strings(struct net_device *dev, uint32_t stringset,
 	}
 }
 
-static int dsa_master_get_phys_port_name(struct net_device *dev,
-					 char *name, size_t len)
-{
-	struct dsa_port *cpu_dp = dev->dsa_ptr;
-
-	if (snprintf(name, len, "p%d", cpu_dp->index) >= len)
-		return -EINVAL;
-
-	return 0;
-}
-
 static int dsa_master_ioctl(struct net_device *dev, struct ifreq *ifr, int cmd)
 {
 	struct dsa_port *cpu_dp = dev->dsa_ptr;
@@ -228,7 +217,6 @@ static int dsa_master_ioctl(struct net_device *dev, struct ifreq *ifr, int cmd)
 
 static const struct dsa_netdevice_ops dsa_netdev_ops = {
 	.ndo_do_ioctl = dsa_master_ioctl,
-	.ndo_get_phys_port_name = dsa_master_get_phys_port_name,
 };
 
 static int dsa_master_ethtool_setup(struct net_device *dev)