Re: [PATCH net-next 2/5] ionic: Report "link_down_events_phy" in ethtool statistics

[Eric Joyner <eric.joyner@amd.com>]

On 5/1/2026 4:39 PM, Jakub Kicinski wrote:
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> 
> 
> On Thu, 30 Apr 2026 20:15:52 -0700 Eric Joyner wrote:
>> The number of times that link has gone down at the port level is tracked
>> by the firmware and sent to the driver via regular DMA writes to an
>> instance of struct ionic_port_status in the driver's memory.
>>
>> This statistic was never reported, but it is useful for diagnostics, so
>> add it to the "ethtool -S` stats output, grouped with the other
>> port-level stats that are contained in struct ionic_port_stats.
> 
> We have a standard stat for this:
> 
> 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;
> };
> 
> 
> IOW the definition of this stat is - ignoring asymetric link faults
> this counter should match between link partners.

So, this is a little awkward to talk about -- we are already filling out that
field with a stat that's calculated by the driver; there's a task that monitors
link transitions and increments it.

But, I'm not sure if that method exists because of older firmwares or cards not
tracking the link_down_event count for us. So, I didn't want to just overwrite
this stat with the value from firmware because then we'd lose the count on cards
running firmware that doesn't do that counting for us.

So that's one reason why I put the stat in the generic ethtool stats output, and
gave it the slightly different name "link_down_events_phy" to distinguish it
(this also matches Mellanox's name for consistency) from this stat in the struct
you posted. Though reading the doc comment you posted, this new stat really does
belong there.

- Eric