Re: [Intel-wired-lan] [PATCH iwl-next v10 10/14] igc: add support for frame preemption verification

[Mor Bar-Gabay <morx.bar.gabay@intel.com>]

On 18/03/2025 5:07, Faizal Rahim wrote:
> This patch implements the "ethtool --set-mm" callback to trigger the
> frame preemption verification handshake.
> 
> Uses the MAC Merge Software Verification (mmsv) mechanism in ethtool
> to perform the verification handshake for igc.
> The structure fpe.mmsv is set by mmsv in ethtool and should remain
> read-only for the driver.
> 
> Other mmsv callbacks:
> a) configure_tx() -> not used yet at this point
>     - igc lacks registers to configure FPE in the transmit direction, so
>       this API is not utilized for now. When igc supports preemptible queue,
>       driver will use this API to manage its configuration.
> 
> b) configure_pmac() -> not used
>     - this callback dynamically controls pmac_enabled at runtime. For
>       example, mmsv calls configure_pmac() and disables pmac_enabled when
>       the link partner goes down, even if the user previously enabled it.
>       The intention is to save power but it is not feasible in igc
>       because it causes an endless adapter reset loop:
> 
>     1) Board A and Board B complete the verification handshake. Tx mode
>        register for both boards are in TSN mode.
>     2) Board B link goes down.
> 
>     On Board A:
>     3) mmsv calls configure_pmac() with pmac_enabled = false.
>     4) configure_pmac() in igc updates a new field based on pmac_enabled.
>        Driver uses this field in igc_tsn_new_flags() to indicate that the
>        user enabled/disabled FPE.
>     5) configure_pmac() in igc calls igc_tsn_offload_apply() to check
>        whether an adapter reset is needed. Calls existing logic in
>        igc_tsn_will_tx_mode_change() and igc_tsn_new_flags().
>     6) Since pmac_enabled is now disabled and no other TSN feature is
>        active, igc_tsn_will_tx_mode_change() evaluates to true because Tx
>        mode will switch from TSN to Legacy.
>     7) Driver resets the adapter.
>     8) Registers are set, and Tx mode switches to Legacy.
>     9) When link partner is up, steps 3–8 repeat, but this time with
>        pmac_enabled = true, reactivating TSN.
>        igc_tsn_will_tx_mode_change() evaluates to true again, since Tx
>        mode will switch from Legacy to TSN.
>    10) Driver resets the adapter.
>    11) Adapter reset completes, registers are set, and Tx mode switches to
>        TSN.
> 
>    On Board B:
>    12) Adapter reset on Board A at step 10 causes it to detect its link
>        partner as down.
>    13) Repeats steps 3–8.
>    14) Once reset adapter on Board A is completed at step 11, it detects
>        its link partner as up.
>    15) Repeats steps 9–11.
> 
>     - this cycle repeats indefinitely. To avoid this issue, igc only uses
>       mmsv.pmac_enabled to track whether FPE is enabled or disabled.
> 
> Co-developed-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
> Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
> Co-developed-by: Choong Yong Liang <yong.liang.choong@linux.intel.com>
> Signed-off-by: Choong Yong Liang <yong.liang.choong@linux.intel.com>
> Co-developed-by: Chwee-Lin Choong <chwee.lin.choong@intel.com>
> Signed-off-by: Chwee-Lin Choong <chwee.lin.choong@intel.com>
> Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
> Signed-off-by: Faizal Rahim <faizal.abdul.rahim@linux.intel.com>
> ---
>   drivers/net/ethernet/intel/Kconfig           |   1 +
>   drivers/net/ethernet/intel/igc/igc.h         |  12 +-
>   drivers/net/ethernet/intel/igc/igc_base.h    |   1 +
>   drivers/net/ethernet/intel/igc/igc_defines.h |   8 +-
>   drivers/net/ethernet/intel/igc/igc_ethtool.c |  21 +++
>   drivers/net/ethernet/intel/igc/igc_main.c    |  52 ++++++-
>   drivers/net/ethernet/intel/igc/igc_tsn.c     | 146 ++++++++++++++++++-
>   drivers/net/ethernet/intel/igc/igc_tsn.h     |  50 +++++++
>   8 files changed, 286 insertions(+), 5 deletions(-)
> 
Tested-by: Mor Bar-Gabay <morx.bar.gabay@intel.com>