net: dsa: Provide CPU port statistics to master netdev

This patch overloads the DSA master netdev, aka CPU Ethernet MAC to also
include switch-side statistics, which is useful for debugging purposes,
when the switch is not properly connected to the Ethernet MAC (duplex
mismatch, (RG)MII electrical issues etc.).

We accomplish this by retaining the original copy of the master netdev's
ethtool_ops, and just overload the 3 operations we care about:
get_sset_count, get_strings and get_ethtool_stats so as to intercept
these calls and call into the original master_netdev ethtool_ops, plus
our own.

We take this approach as opposed to providing a set of DSA helper
functions that would retrive the CPU port's statistics, because the
entire purpose of DSA is to allow unmodified Ethernet MAC drivers to be
used as CPU conduit interfaces, therefore, statistics overlay in such
drivers would simply not scale.

The new ethtool -S <iface> output would therefore look like this now:
<iface> statistics
p<2 digits cpu port number>_<switch MIB counter names>

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 0 deletions

diff --git a/include/net/dsa.h b/include/net/dsa.h
index 2d280aba97e2..8e86af87c84f 100644
--- a/include/net/dsa.h
+++ b/include/net/dsa.h
@@ -111,6 +111,11 @@ struct dsa_switch_tree {
 	enum dsa_tag_protocol	tag_protocol;
 
 	/*
+	 * Original copy of the master netdev ethtool_ops
+	 */
+	struct ethtool_ops	master_ethtool_ops;
+
+	/*
 	 * The switch and port to which the CPU is attached.
 	 */
 	s8			cpu_switch;