Re: [PATCH net-next v2] ionic: Add .get_fec_stats ethtool handler

On Fri, Aug 14, 2026 at 05:33:12PM -0700, Eric Joyner wrote:
> Reports FEC statistics totals and an 802.3ck FEC histogram. Per-lane
> counts currently aren't supported. Every counter reported here comes
> from the RS decoder, including fec_corrected_bits_total despite its
> name, and the only histogram format firmware produces is the 16-bin one
> from RS(544,514), so nothing is reported unless RS is the active FEC
> mode.
> 
> These are physical port counters, so virtual functions are skipped the
> same way ionic_get_link_ext_stats() skips them, rather than reporting the
> port's counters as if they belonged to the VF.
> 
> The reporting of these statistics is gated by DEV_CAP_EXTRA_STATS and
> checks for IONIC_STAT_INVALID, since only the newest devices support
> reporting all of these stats. Older devices can only report some of the
> statistics or not at all, and so the output will properly exclude those
> unsupported statistics.
> 
> Assisted-by: Claude:claude-opus-5
> Signed-off-by: Eric Joyner <[email protected]>
> Reviewed-by: Vadim Fedorenko <[email protected]>
> ---
> Reposting since v1 was too old to apply. This also addresses the netdev
> AI review comments left on v1:
> https://netdev-ai.bots.linux.dev/sashiko/#/patchset/[email protected]
> 
> That review also flagged a NULL dereference in ionic_get_fecparam().
> It predates this patch, so it is fixed separately in the net tree
> rather than here:
>   [PATCH net 0/3] ionic: fix port_info lifetime problems around device reset
>   https://lore.kernel.org/netdev/[email protected]/T/#t
> 
> Vadim's Reviewed-by from v1 is retained. The only change to the code
> since he reviewed it is the histogram bin latch listed below.
> ---
> Changes in v2:
> - Latch each histogram bin into a local before testing it against
>   IONIC_STAT_INVALID, so the sentinel check and the store cannot be
>   folded into two separate reads of the firmware-updated DMA buffer.
> - Explain in the commit message why the RS FEC check gates every
>   reported counter rather than just the histogram: they all come from
>   the RS decoder, including fec_corrected_bits_total despite its name.
> - Rebased onto current net-next.
> - Link to v1: https://lore.kernel.org/r/[email protected]
> ---
>  .../net/ethernet/pensando/ionic/ionic_ethtool.c    | 86 ++++++++++++++++++++++
>  1 file changed, 86 insertions(+)
> 
> diff --git a/drivers/net/ethernet/pensando/ionic/ionic_ethtool.c b/drivers/net/ethernet/pensando/ionic/ionic_ethtool.c
> index c4ab4b5caa0a..2f2b5076dcf4 100644
> --- a/drivers/net/ethernet/pensando/ionic/ionic_ethtool.c
> +++ b/drivers/net/ethernet/pensando/ionic/ionic_ethtool.c
> @@ -441,6 +441,91 @@ static int ionic_get_fecparam(struct net_device *netdev,
>  	return 0;
>  }
>  
> +#define IONIC_FEC_STAT(dst, src)			\
> +	do {						\
> +		__le64 __val = (src);			\
> +							\
> +		if (__val != IONIC_STAT_INVALID)	\
> +			(dst) = le64_to_cpu(__val);	\
> +	} while (0)

Hi Eric,

There is an AI-generated review of this patch available at
https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260814-ionic-get-fec-stats-v2-1-13f0e7d2e702%40amd.com

In that review, the following stands out to me.
I'd appreciate it if you could take a look over it in particular.

  The v2 changelog says the per-bin local "latches" the value so "the
  sentinel check and the store cannot be folded into two separate reads of
  the firmware-updated DMA buffer".  Is that guaranteed by this code?

  Both this macro and the loop body in ionic_fill_fec_hist() use plain,
  non-volatile loads:

	__le64 __val = (src);
	if (__val != IONIC_STAT_INVALID)
		(dst) = le64_to_cpu(__val);

  and

	__le64 val = port_extra_stats->fec_codeword_error_bin[i];
	if (val == IONIC_STAT_INVALID)
		return;
	hist->values[i].sum = le64_to_cpu(val);

  Nothing stops the compiler from discarding the local and re-loading the
  word from the coherent buffer for the comparison and again for the store.

  Would READ_ONCE() on each word, or a memcpy() of the block, be needed to
  actually get the single-read property described in the changelog?

  The same applies to the struct assignment in ionic_get_fec_stats():

	port_extra_stats = port_info->extra_stats;

  This is an ordinary aggregate copy out of memory the device writes
  asynchronously, so members may be re-read at each later use rather than
  coming from a stack snapshot.

  If a word transitions while being read, can the 0xffffffffffffffff
  sentinel that ionic_port_init() memsets into extra_stats be reported to
  user space as a real counter, or a counter firmware did fill in be
  dropped, and can the 16 histogram bins end up stitched together from
  different firmware snapshots?

...