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Kurt Kanzenbach 8fdfa207af igc: Restore default Qbv schedule when changing channels 
[ Upstream commit 41a9a6826f ]

The Multi-queue Priority (MQPRIO) and Earliest TxTime First (ETF) offloads
utilize the Time Sensitive Networking (TSN) Tx mode. This mode is always
coupled to IEEE 802.1Qbv time aware shaper (Qbv). Therefore, the driver
sets a default Qbv schedule of all gates opened and a cycle time of
1s. This schedule is set during probe.

However, the following sequence of events lead to Tx issues:

 - Boot a dual core system
   igc_probe():
     igc_tsn_clear_schedule():
       -> Default Schedule is set
       Note: At this point the driver has allocated two Tx/Rx queues, because
       there are only two CPUs.

 - ethtool -L enp3s0 combined 4
   igc_ethtool_set_channels():
     igc_reinit_queues()
       -> Default schedule is gone, per Tx ring start and end time are zero

  - tc qdisc replace dev enp3s0 handle 100 parent root mqprio \
      num_tc 4 map 3 3 2 2 0 1 1 1 3 3 3 3 3 3 3 3 \
      queues 1@0 1@1 1@2 1@3 hw 1
    igc_tsn_offload_apply():
      igc_tsn_enable_offload():
        -> Writes zeros to IGC_STQT(i) and IGC_ENDQT(i), causing Tx to stall/fail

Therefore, restore the default Qbv schedule after changing the number of
channels.

Furthermore, add a restriction to not allow queue reconfiguration when
TSN/Qbv is enabled, because it may lead to inconsistent states.

Fixes: c814a2d2d4 ("igc: Use default cycle 'start' and 'end' values for queues")
Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Tested-by: Avigail Dahan <avigailx.dahan@intel.com>
Acked-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2026-01-30 10:28:38 +01:00
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README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.