ethtool: linkstate: add a statistic for PHY down events

The previous attempt to augment carrier_down (see Link)
was not met with much enthusiasm so let's do the simple
thing of exposing what some devices already maintain.
Add a common ethtool statistic for link going down.
Currently users have to maintain per-driver mapping
to extract the right stat from the vendor-specific ethtool -S
stats. carrier_down does not fit the bill because it counts
a lot of software related false positives.

Add the statistic to the extended link state API to steer
vendors towards implementing all of it.

Implement for bnxt and all Linux-controlled PHYs. mlx5 and (possibly)
enic also have a counter for this but I leave the implementation
to their maintainers.

Link: https://lore.kernel.org/r/20220520004500.2250674-1-kuba@kernel.org
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Michael Chan <michael.chan@broadcom.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Link: https://lore.kernel.org/r/20221104190125.684910-1-kuba@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

2 files changed, 20 insertions, 0 deletions

diff --git a/include/linux/ethtool.h b/include/linux/ethtool.h
index 99dc7bfbcd3c..5c51c7fda32a 100644
--- a/include/linux/ethtool.h
+++ b/include/linux/ethtool.h
@@ -125,6 +125,20 @@ struct ethtool_link_ext_state_info {
 	};
 };
 
+struct ethtool_link_ext_stats {
+	/* Custom Linux statistic for PHY level link down events.
+	 * In a simpler world it should be equal to netdev->carrier_down_count
+	 * unfortunately netdev also counts local reconfigurations which don't
+	 * actually take the physical link down, not to mention NC-SI which,
+	 * if present, keeps the link up regardless of host state.
+	 * This statistic counts when PHY _actually_ went down, or lost link.
+	 *
+	 * Note that we need u64 for ethtool_stats_init() and comparisons
+	 * to ETHTOOL_STAT_NOT_SET, but only u32 is exposed to the user.
+	 */
+	u64 link_down_events;
+};
+
 /**
  * ethtool_rxfh_indir_default - get default value for RX flow hash indirection
  * @index: Index in RX flow hash indirection table
@@ -481,6 +495,7 @@ struct ethtool_module_power_mode_params {
  *	do not attach ext_substate attribute to netlink message). If link_ext_state
  *	and link_ext_substate are unknown, return -ENODATA. If not implemented,
  *	link_ext_state and link_ext_substate will not be sent to userspace.
+ * @get_link_ext_stats: Read extra link-related counters.
  * @get_eeprom_len: Read range of EEPROM addresses for validation of
  *	@get_eeprom and @set_eeprom requests.
  *	Returns 0 if device does not support EEPROM access.
@@ -652,6 +667,8 @@ struct ethtool_ops {
 	u32	(*get_link)(struct net_device *);
 	int	(*get_link_ext_state)(struct net_device *,
 				      struct ethtool_link_ext_state_info *);
+	void	(*get_link_ext_stats)(struct net_device *dev,
+				      struct ethtool_link_ext_stats *stats);
 	int	(*get_eeprom_len)(struct net_device *);
 	int	(*get_eeprom)(struct net_device *,
 			      struct ethtool_eeprom *, u8 *);
diff --git a/include/linux/phy.h b/include/linux/phy.h
index ddf66198f751..9a3752c0c444 100644
--- a/include/linux/phy.h
+++ b/include/linux/phy.h
@@ -600,6 +600,7 @@ struct macsec_ops;
  * @psec: Pointer to Power Sourcing Equipment control struct
  * @lock:  Mutex for serialization access to PHY
  * @state_queue: Work queue for state machine
+ * @link_down_events: Number of times link was lost
  * @shared: Pointer to private data shared by phys in one package
  * @priv: Pointer to driver private data
  *
@@ -723,6 +724,8 @@ struct phy_device {
 
 	int pma_extable;
 
+	unsigned int link_down_events;
+
 	void (*phy_link_change)(struct phy_device *phydev, bool up);
 	void (*adjust_link)(struct net_device *dev);