[PATCH 5.15 127/207] net: stmmac: Avoid DMA_CHAN_CONTROL write if no Split Header support

Greg Kroah-Hartman
2021-12-06T15:56:05Z

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;
}