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    Subject[PATCH 5.15 127/207] net: stmmac: Avoid DMA_CHAN_CONTROL write if no Split Header support
    Date
    From: Vincent Whitchurch <vincent.whitchurch@axis.com>

    commit f8e7dfd6fdabb831846ab1970a875746559d491b upstream.

    The driver assumes that split headers can be enabled/disabled without
    stopping/starting the device, so it writes DMA_CHAN_CONTROL from
    stmmac_set_features(). However, on my system (IP v5.10a without Split
    Header support), simply writing DMA_CHAN_CONTROL when DMA is running
    (for example, with the commands below) leads to a TX watchdog timeout.

    host$ socat TCP-LISTEN:1024,fork,reuseaddr - &
    device$ ethtool -K eth0 tso off
    device$ ethtool -K eth0 tso on
    device$ dd if=/dev/zero bs=1M count=10 | socat - TCP4:host:1024
    <tx watchdog timeout>

    Note that since my IP is configured without Split Header support, the
    driver always just reads and writes the same value to the
    DMA_CHAN_CONTROL register.

    I don't have access to any platforms with Split Header support so I
    don't know if these writes to the DMA_CHAN_CONTROL while DMA is running
    actually work properly on such systems. I could not find anything in
    the databook that says that DMA_CHAN_CONTROL should not be written when
    the DMA is running.

    But on systems without Split Header support, there is in any case no
    need to call enable_sph() in stmmac_set_features() at all since SPH can
    never be toggled, so we can avoid the watchdog timeout there by skipping
    this call.

    Fixes: 8c6fc097a2f4acf ("net: stmmac: gmac4+: Add Split Header support")
    Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 11 ++++++-----
    1 file changed, 6 insertions(+), 5 deletions(-)

    --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
    +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
    @@ -5531,8 +5531,6 @@ static int stmmac_set_features(struct ne
    netdev_features_t features)
    {
    struct stmmac_priv *priv = netdev_priv(netdev);
    - bool sph_en;
    - u32 chan;

    /* Keep the COE Type in case of csum is supporting */
    if (features & NETIF_F_RXCSUM)
    @@ -5544,10 +5542,13 @@ static int stmmac_set_features(struct ne
    */
    stmmac_rx_ipc(priv, priv->hw);

    - sph_en = (priv->hw->rx_csum > 0) && priv->sph;
    + if (priv->sph_cap) {
    + bool sph_en = (priv->hw->rx_csum > 0) && priv->sph;
    + u32 chan;

    - for (chan = 0; chan < priv->plat->rx_queues_to_use; chan++)
    - stmmac_enable_sph(priv, priv->ioaddr, sph_en, chan);
    + for (chan = 0; chan < priv->plat->rx_queues_to_use; chan++)
    + stmmac_enable_sph(priv, priv->ioaddr, sph_en, chan);
    + }

    return 0;
    }

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