Subject: Re: [Intel-wired-lan] [PATCH iwl-net v2 1/1] igc: Fix packet still tx after gate close by reducing i226 MAC retry buffer

From: Mor Bar-Gabay <[email-masked]>
Date: Thu, 1 Aug 2024 10:26:27 +0300

On 06/07/2024 18:38, Faizal Rahim wrote:
> Testing uncovered that even when the taprio gate is closed, some packets
> still transmit.
> 
> According to i225/6 hardware errata [1], traffic might overflow the
> planned QBV window. This happens because MAC maintains an internal buffer,
> primarily for supporting half duplex retries. Therefore, even when the
> gate closes, residual MAC data in the buffer may still transmit.
> 
> To mitigate this for i226, reduce the MAC's internal buffer from 192 bytes
> to the recommended 88 bytes by modifying the RETX_CTL register value.
> 
> This follows guidelines from:
> [1] Ethernet Controller I225/I22 Spec Update Rev 2.1 Errata Item 9:
>      TSN: Packet Transmission Might Cross Qbv Window
> [2] I225/6 SW User Manual Rev 1.2.4: Section 8.11.5 Retry Buffer Control
> 
> Note that the RETX_CTL register can't be used in TSN mode because half
> duplex feature cannot coexist with TSN.
> 
> Test Steps:
> 1.  Send taprio cmd to board A:
>      tc qdisc replace dev enp1s0 parent root handle 100 taprio \
>      num_tc 4 \
>      map 3 2 1 0 3 3 3 3 3 3 3 3 3 3 3 3 \
>      queues 1@0 1@1 1@2 1@3 \
>      base-time 0 \
>      sched-entry S 0x07 500000 \
>      sched-entry S 0x0f 500000 \
>      flags 0x2 \
>      txtime-delay 0
> 
>      Note that for TC3, gate should open for 500us and close for another
>      500us.
> 
> 3.  Take tcpdump log on Board B.
> 
> 4.  Send udp packets via UDP tai app from Board A to Board B.
> 
> 5.  Analyze tcpdump log via wireshark log on Board B. Ensure that the
>      total time from the first to the last packet received during one cycle
>      for TC3 does not exceed 500us.
> 
> Signed-off-by: Faizal Rahim <[email-masked]>
> Acked-by: Vinicius Costa Gomes <[email-masked]>
> ---
> v1: https://patchwork.kernel.org/project/netdevbpf/patch/[email-masked]/
> 
> Changelog:
> v1 -> v2
> - Update commit description (Paul).
> - Rename qbvfullth -> qbvfullthreshold (Paul).
> ---
>   drivers/net/ethernet/intel/igc/igc_defines.h |  6 ++++
>   drivers/net/ethernet/intel/igc/igc_tsn.c     | 34 ++++++++++++++++++++
>   2 files changed, 40 insertions(+)
> 
Tested-by: Mor Bar-Gabay <[email-masked]>