ionic: Expose more port stats to ethtool

The primary aim of this patchset is to support the reporting of new port statistics (and one old one) that firmware sends to the driver; these include general FEC codeword stats and the FEC histogram. A scheme for these extra stats is introduced in order to prevent devices that don't support these new statistics from unconditionally setting them or reporting them in ethtool.

---
v5:
Address new Sashiko AI comments and previous feedback
patch 2:
- Remove additional unused enums that were only used by struct ionic_port_pb_stats
- Change IONIC_STAT_INVALID to use (~0ULL) instead of ((__le64)-1) to avoid sparse warnings (and moved to patch 3)
patch 4:
- Change ethtool link_down_events count to use firmware-derived value; handle overflow and set count to zero on driver load and resets. Finally drop the driver-calculated value and ethtool general stat counter and only report count in the ethtool extended link stat structure.
patch 5:
- Add check for NULL port_info in .get_fec_stats() callback in order to prevent a potential NULL pointer dereference, similar to other ethtool callbacks.

v4:
- A big addition is a new scheme where the driver will only report the new statistics supported by firmware if the firmware sets the statistic value to something that isn't invalid; more details in patch 3, and this is used in patch 5 to prevent FEC stats from being unconditionally reported on devices/firmware versions that don't support these stats.
- The link_down_count from firmware mentioned in v2 was moved back to an entry in the general ethtool statistics; the existing driver-calculated value for the ethtool ext link is more appropriate due to the firmware value being a small size and not resetting between driver loads.
- Add netdev_err_once() call recommended by Sashiko for ethtool handler
- Drop devcmd retry logic patch from previous versions for now; explicitly include Brett's patch from another patchset to fix the ionic_get_link_ext_stats() PF/VF check

v3:
Address issues mostly found by Sashiko:
- Fix potential return of uninitialized variable in __ionic_dev_cmd_wait()
- Fix bounds of wait in __ionic_dev_cmd_wait() to prevent function from giving up prematurely now that the wait period has changed
- Add NULL check to ionic_get_link_ext_stats(), following the example set by ionic_get_link_ksettings()
- Add missing le16_to_cpu() when copying link_down_count from firmware

v2:
- Add missing cpu_to_le64() to FEC histogram stat assignment
- Remove unused pb_stats field that's replaced by the new FEC/extra stats
- Replace ethtool ext link stat with firmware stat instead of adding the firmware stat to general ethtool statistics; remove old driver calculated stat
- Add explanation for what EAGAIN return value could be used for in commit message

Brett Creeley (1):
ionic: Fix check in ionic_get_link_ext_stats

Eric Joyner (4):
ionic: Update ionic_if.h with new extra port stats
ionic: Report "rx_bits_phy" stat to ethtool
ionic: Get "link_down_count" ext link stat from firmware
ionic: Add .get_fec_stats ethtool handler

 .../net/ethernet/pensando/ionic/ionic_dev.c   |  10 ++
 .../net/ethernet/pensando/ionic/ionic_dev.h   |   6 +
 .../ethernet/pensando/ionic/ionic_ethtool.c   | 104 +++++++++++++++++-
 .../net/ethernet/pensando/ionic/ionic_if.h    |  64 ++---------
 .../net/ethernet/pensando/ionic/ionic_lif.c   |   4 +-
 .../net/ethernet/pensando/ionic/ionic_lif.h   |   1 -
 .../net/ethernet/pensando/ionic/ionic_main.c  |   8 ++
 .../net/ethernet/pensando/ionic/ionic_stats.c |  65 ++++++++++-
 .../net/ethernet/pensando/ionic/ionic_stats.h |   2 +
 9 files changed, 206 insertions(+), 58 deletions(-)

base-commit: 93790c374b9d77f3db15786d7d432872d92751cf

2.17.1