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/[email protected]
Reviewed-by: Florian Fainelli <[email protected]>
Reviewed-by: Michael Chan <[email protected]>
Reviewed-by: Andrew Lunn <[email protected]>
Signed-off-by: Jakub Kicinski <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Paolo Abeni <[email protected]>

1 files changed, 1 insertions, 0 deletions

diff --git a/drivers/net/phy/phy.c b/drivers/net/phy/phy.c
index e741d8aebffe..e5b6cb1a77f9 100644
--- a/drivers/net/phy/phy.c
+++ b/drivers/net/phy/phy.c
@@ -67,6 +67,7 @@ static void phy_link_down(struct phy_device *phydev)
 {
 	phydev->phy_link_change(phydev, false);
 	phy_led_trigger_change_speed(phydev);
+	WRITE_ONCE(phydev->link_down_events, phydev->link_down_events + 1);
 }
 
 static const char *phy_pause_str(struct phy_device *phydev)