netdev - Re: Debugging Ethernet issues

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Date:   Mon, 14 Nov 2016 09:32:10 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Mason <slash.tmp@...e.fr>, Andrew Lunn <andrew@...n.ch>
Cc:     netdev <netdev@...r.kernel.org>, Mans Rullgard <mans@...sr.com>,
        Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Zach Brown <zach.brown@...com>,
        Shaohui Xie <shaohui.xie@....com>,
        Tim Beale <tim.beale@...iedtelesis.co.nz>,
        Brian Hill <brian@...ston-radar.com>,
        Vince Bridgers <vbridgers2013@...il.com>,
        Balakumaran Kannan <kumaran.4353@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Sebastian Frias <sf84@...oste.net>,
        Kirill Kapranov <kapranoff@...ox.ru>
Subject: Re: Debugging Ethernet issues

On 11/14/2016 07:33 AM, Mason wrote:
> 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
> 

And the time difference is clearly accounted for auto-negotiation time
here, as you can see it takes about 3 seconds for Gigabit Ethernet to
auto-negotiate and that seems completely acceptable and normal to me
since it is a more involved process than lower speeds.

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

Because your link partner advertises flow control, and that's what
phydev->pause and phydev->asym_pause report (I know it's confusing, but
that's what it is at the moment).

> 
> # 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?

Yes, switches can support flow control aka pause frames, and unless they
are configurable, they typically advertise what their EEPROM has defined
for them, so most likely the full auto-negotiated spectrum:
10/100/1000Mbps and support for flow control, but your mileage may vary
of course.
-- 
Florian