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    Subject[PATCH 5.16 1012/1039] net: mscc: ocelot: dont let phylink re-enable TX PAUSE on the NPI port
    Date
    From: Vladimir Oltean <vladimir.oltean@nxp.com>

    commit 33cb0ff30cff104e753f7882c99e54cf67ea7903 upstream.

    Since commit b39648079db4 ("net: mscc: ocelot: disable flow control on
    NPI interface"), flow control should be disabled on the DSA CPU port
    when used in NPI mode.

    However, the commit blamed in the Fixes: tag below broke this, because
    it allowed felix_phylink_mac_link_up() to overwrite SYS_PAUSE_CFG_PAUSE_ENA
    for the DSA CPU port.

    This issue became noticeable since the device tree update from commit
    8fcea7be5736 ("arm64: dts: ls1028a: mark internal links between Felix
    and ENETC as capable of flow control").

    The solution is to check whether this is the currently configured NPI
    port from ocelot_phylink_mac_link_up(), and to not modify the statically
    disabled PAUSE frame transmission if it is.

    When the port is configured for lossless mode as opposed to tail drop
    mode, but the link partner (DSA master) doesn't observe the transmitted
    PAUSE frames, the switch termination throughput is much worse, as can be
    seen below.

    Before:

    root@debian:~# iperf3 -c 192.168.100.2
    Connecting to host 192.168.100.2, port 5201
    [ 5] local 192.168.100.1 port 37504 connected to 192.168.100.2 port 5201
    [ ID] Interval Transfer Bitrate Retr Cwnd
    [ 5] 0.00-1.00 sec 28.4 MBytes 238 Mbits/sec 357 22.6 KBytes
    [ 5] 1.00-2.00 sec 33.6 MBytes 282 Mbits/sec 426 19.8 KBytes
    [ 5] 2.00-3.00 sec 34.0 MBytes 285 Mbits/sec 343 21.2 KBytes
    [ 5] 3.00-4.00 sec 32.9 MBytes 276 Mbits/sec 354 22.6 KBytes
    [ 5] 4.00-5.00 sec 32.3 MBytes 271 Mbits/sec 297 18.4 KBytes
    ^C[ 5] 5.00-5.06 sec 2.05 MBytes 270 Mbits/sec 45 19.8 KBytes
    - - - - - - - - - - - - - - - - - - - - - - - - -
    [ ID] Interval Transfer Bitrate Retr
    [ 5] 0.00-5.06 sec 163 MBytes 271 Mbits/sec 1822 sender
    [ 5] 0.00-5.06 sec 0.00 Bytes 0.00 bits/sec receiver

    After:

    root@debian:~# iperf3 -c 192.168.100.2
    Connecting to host 192.168.100.2, port 5201
    [ 5] local 192.168.100.1 port 49470 connected to 192.168.100.2 port 5201
    [ ID] Interval Transfer Bitrate Retr Cwnd
    [ 5] 0.00-1.00 sec 112 MBytes 941 Mbits/sec 259 143 KBytes
    [ 5] 1.00-2.00 sec 110 MBytes 920 Mbits/sec 329 144 KBytes
    [ 5] 2.00-3.00 sec 112 MBytes 936 Mbits/sec 255 144 KBytes
    [ 5] 3.00-4.00 sec 110 MBytes 927 Mbits/sec 355 105 KBytes
    [ 5] 4.00-5.00 sec 110 MBytes 926 Mbits/sec 350 156 KBytes
    [ 5] 5.00-6.00 sec 110 MBytes 925 Mbits/sec 305 148 KBytes
    [ 5] 6.00-7.00 sec 110 MBytes 924 Mbits/sec 320 143 KBytes
    [ 5] 7.00-8.00 sec 110 MBytes 925 Mbits/sec 273 97.6 KBytes
    [ 5] 8.00-9.00 sec 109 MBytes 913 Mbits/sec 299 141 KBytes
    [ 5] 9.00-10.00 sec 110 MBytes 922 Mbits/sec 287 146 KBytes
    - - - - - - - - - - - - - - - - - - - - - - - - -
    [ ID] Interval Transfer Bitrate Retr
    [ 5] 0.00-10.00 sec 1.08 GBytes 926 Mbits/sec 3032 sender
    [ 5] 0.00-10.00 sec 1.08 GBytes 925 Mbits/sec receiver

    Fixes: de274be32cb2 ("net: dsa: felix: set TX flow control according to the phylink_mac_link_up resolution")
    Reported-by: Xiaoliang Yang <xiaoliang.yang_1@nxp.com>
    Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
    Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/net/ethernet/mscc/ocelot.c | 5 ++++-
    1 file changed, 4 insertions(+), 1 deletion(-)

    --- a/drivers/net/ethernet/mscc/ocelot.c
    +++ b/drivers/net/ethernet/mscc/ocelot.c
    @@ -692,7 +692,10 @@ void ocelot_phylink_mac_link_up(struct o

    ocelot_write_rix(ocelot, 0, ANA_POL_FLOWC, port);

    - ocelot_fields_write(ocelot, port, SYS_PAUSE_CFG_PAUSE_ENA, tx_pause);
    + /* Don't attempt to send PAUSE frames on the NPI port, it's broken */
    + if (port != ocelot->npi)
    + ocelot_fields_write(ocelot, port, SYS_PAUSE_CFG_PAUSE_ENA,
    + tx_pause);

    /* Undo the effects of ocelot_phylink_mac_link_down:
    * enable MAC module

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