netdev - Re: [PATCH 1/2] [for 4.13] net: qcom/emac: disable flow control autonegotiation by default

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Date:   Wed, 02 Aug 2017 11:35:31 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     timur@...eaurora.org
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH 1/2] [for 4.13] net: qcom/emac: disable flow control
 autonegotiation by default

From: Timur Tabi <timur@...eaurora.org>
Date: Wed, 2 Aug 2017 13:23:18 -0500

> On 08/02/2017 12:54 PM, David Miller wrote:
>> And if this kind of thing matters to the user, they will have a
>> software or hardware watchdog driver enabled to break out of this
>> situation.
> 
> The problem is that the user is not going to expect that the EMAC can
> disable the nearby switch(es) when the kernel is hung and not rebooted
> quickly enough.  Internally, this bug/feature has caused quite a bit
> of mayhem, so the problem is real.  No cares about enabling flow
> control -- it just happens to be enabled on some systems where the
> switch agrees to it.  So random individuals can't debug the hardware
> because suddenly the EMAC has gone haywire and disabled the local
> network.

Again, any serious installation will have a system watchdog enabled
which will break the pause frame bomb.