Subject: Re: Debugging Ethernet issues

From: Mason <[email-masked]>
Date: Mon, 14 Nov 2016 16:33:48 +0100

On 14/11/2016 15:58, Mason wrote:

> nb8800 26000.ethernet eth0: Link is Up - 100Mbps/Full - flow control rx/tx
> vs
> nb8800 26000.ethernet eth0: Link is Up - 100Mbps/Full - flow control off
> 
> I'm not sure whether "flow control" is relevant...

Based on phy_print_status()
phydev->pause ? "rx/tx" : "off"
I added the following patch.

diff --git a/drivers/net/ethernet/aurora/nb8800.c b/drivers/net/ethernet/aurora/nb8800.c
index defc22a15f67..4e758c1cfa4e 100644
--- a/drivers/net/ethernet/aurora/nb8800.c
+++ b/drivers/net/ethernet/aurora/nb8800.c
@@ -667,6 +667,8 @@ static void nb8800_link_reconfigure(struct net_device *dev)
        struct phy_device *phydev = priv->phydev;
        int change = 0;
 
+       printk("%s from %pf\n", __func__, __builtin_return_address(0));
+
        if (phydev->link) {
                if (phydev->speed != priv->speed) {
                        priv->speed = phydev->speed;
@@ -1274,9 +1276,9 @@ static int nb8800_hw_init(struct net_device *dev)
        nb8800_writeb(priv, NB8800_PQ2, val & 0xff);
 
        /* Auto-negotiate by default */
-       priv->pause_aneg = true;
-       priv->pause_rx = true;
-       priv->pause_tx = true;
+       priv->pause_aneg = false;
+       priv->pause_rx = false;
+       priv->pause_tx = false;
 
        nb8800_mc_init(dev, 0);

Connected to 1000 Mbps switch:

# time udhcpc | while read LINE; do date; echo $LINE; done
Thu Jan  1 00:00:22 UTC 1970
udhcpc (v1.22.1) started
Thu Jan  1 00:00:22 UTC 1970
Sending discover...
[   24.565346] nb8800_link_reconfigure from phy_state_machine
Thu Jan  1 00:00:25 UTC 1970
Sending discover...
[   26.575402] nb8800_link_reconfigure from phy_state_machine
[   26.580972] nb8800 26000.ethernet eth0: Link is Up - 1Gbps/Full - flow control rx/tx
Thu Jan  1 00:00:28 UTC 1970
Sending discover...
Thu Jan  1 00:00:29 UTC 1970
Sending select for 172.27.64.58...
Thu Jan  1 00:00:29 UTC 1970
Lease of 172.27.64.58 obtained, lease time 604800
Thu Jan  1 00:00:29 UTC 1970
deleting routers
Thu Jan  1 00:00:29 UTC 1970
adding dns 172.27.0.17

real    0m7.388s
user    0m0.040s
sys     0m0.090s

Connected to 100 Mbps switch:

# time udhcpc | while read LINE; do date; echo $LINE; done
Thu Jan  1 00:00:14 UTC 1970
udhcpc (v1.22.1) started
Thu Jan  1 00:00:15 UTC 1970
Sending discover...
[   16.968621] nb8800_link_reconfigure from phy_state_machine
[   17.975359] nb8800_link_reconfigure from phy_state_machine
[   17.980923] nb8800 26000.ethernet eth0: Link is Up - 100Mbps/Full - flow control rx/tx
Thu Jan  1 00:00:18 UTC 1970
Sending discover...
Thu Jan  1 00:00:19 UTC 1970
Sending select for 172.27.64.58...
Thu Jan  1 00:00:19 UTC 1970
Lease of 172.27.64.58 obtained, lease time 604800
Thu Jan  1 00:00:19 UTC 1970
deleting routers
Thu Jan  1 00:00:19 UTC 1970
adding dns 172.27.0.17

real    0m4.355s
user    0m0.043s
sys     0m0.083s

OK, so now it works (by accident?) even on 100 Mbps switch, but it still
prints "flow control rx/tx"...

# ethtool -a eth0
Pause parameters for eth0:
Autonegotiate:  off
RX:             off
TX:             off

These values make sense considering my changes in the driver.

Are 100 Mbps switches supposed to support these pause features,
and are they supposed to be able to auto-negotiate them?

Regards.