netdev - Re: [PATCH] 8139too: send NETDEV_CHANGE manually when autoneg is disabled

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Date:	Thu, 7 Mar 2013 11:27:40 +0100
From:	Veaceslav Falico <vfalico@...hat.com>
To:	David Miller <davem@...emloft.net>
Cc:	bhutchings@...arflare.com, netdev@...r.kernel.org,
	wfp5p@...ginia.edu, jasowang@...hat.com, junchangwang@...il.com,
	greearb@...delatech.com, ivecera@...hat.com
Subject: Re: [PATCH] 8139too: send NETDEV_CHANGE manually when autoneg is
 disabled

On Wed, Mar 06, 2013 at 03:53:23PM -0500, David Miller wrote:
>From: Ben Hutchings <bhutchings@...arflare.com>
>Date: Wed, 6 Mar 2013 20:22:52 +0000
>
>> On Wed, 2013-03-06 at 20:06 +0100, Veaceslav Falico wrote:
>>> When setting autoneg off (with any additional parameters, like
>>> speed/duplex), 8139too doesn't do an interface reset, and thus doesn't
>>> notify anyone that its speed/duplex might have changed (bonding and bridge
>>> will not see the speed changes, per example).
>>>
>>> Verify if we've force_media and send notification manually, so that the
>>> listeners have a chance to see the changes. It's quite ugly, however I
>>> don't see anything better.
>>
>> Isn't this really a bug in mii_check_media()?  It shouldn't shortcut the
>> calls to netif_carrier_{off,on}() just because mii->force_media is set.
>
>I think mii_check_media() is responsible for handling this too.

The mii_check_media() doesn't get called, AFAIK. The problem here is that,
after we call ethtool -s eth0 autoneg off speed X, with eth0 being
8139too, the speed/autoneg options are changed via mii_ethtool_sset(),
however the interface itself isn't down'ed/up'ed, and thus no NETDEV_
notifications are sent.

Other drivers either explicitly reset the interface after
ethtool.set_settings() call (like netxen_nic using ndo_close()/ndo_open()),
do it on the logic level (tg3) without involving mii_ethtool_sset(), or
just reset on their own (e100 iirc), so that most of them are responsible
for somehow triggering these events.

Silently changing speed can break things a bit - bonding relies on
interface speeds for 802.3ad/alb/tlb/active-backup iirc, bridge relies on
stp port cost etc. and they all get it via NETDEV_ notifications. So
without them, they would end up with outdated data, per example (eth2 being
8139too):

darkmag:~#grep 'Interface\|Speed' /proc/net/bonding/bond0
Slave Interface: eth0
Speed: 100 Mbps
Slave Interface: eth2
Speed: 100 Mbps
darkmag:~#ethtool -s eth2 autoneg off speed 10
darkmag:~#cat /sys/class/net/eth2/speed
10
darkmag:~#grep 'Interface\|Speed' /proc/net/bonding/bond0
Slave Interface: eth0
Speed: 100 Mbps
Slave Interface: eth2
Speed: 100 Mbps

However, I think that mii_check_media() is also wrong :), though I didn't
really dig into it. I'll check it when I'll have time.
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