linux-kernel - Re: [PATCH net-next] net: dsa: set random switch address

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Message-ID: <87k200vvsl.fsf@weeman.i-did-not-set--mail-host-address--so-tickle-me>
Date:   Thu, 12 Oct 2017 18:35:54 -0400
From:   Vivien Didelot <vivien.didelot@...oirfairelinux.com>
To:     Florian Fainelli <f.fainelli@...il.com>, netdev@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel@...oirfairelinux.com,
        "David S. Miller" <davem@...emloft.net>,
        Andrew Lunn <andrew@...n.ch>
Subject: Re: [PATCH net-next] net: dsa: set random switch address

Hi Florian,

Florian Fainelli <f.fainelli@...il.com> writes:

> On 10/12/2017 03:10 PM, Vivien Didelot wrote:
>> An Ethernet switch may support having a MAC address, which can be used
>> as the switch's source address in transmitted full-duplex Pause frames.
>> 
>> If a DSA switch supports the related .set_addr operation, the DSA core
>> sets the master's MAC address on the switch.
>> 
>> This won't make sense anymore in a multi-CPU ports system, because there
>> won't be a unique master device assigned to a switch tree.
>
> Thus far, everything you have said is true, but why we should do it,
> that is: what if we don't, needs to be explained. Does that create a
> problem with the generation of pause frames throughout the switch fabric?
>
>> 
>> To fix this, assign a random MAC address to the switch chip instead.
>
> Maybe this is something that should be removed entirely from the DSA
> core and pushed into the individual switch drivers instead. dsa_loop
> implements it for code coverage, but that does not do anything.
>
> set_addr is confusing in that you may think it could be used to program
> the switch with the MAC address of the CPU/management port such that you
> can disable MAC address learning on said port, but in fact, that's not
> how it is used.

You are correct. So what I can do is assign a random MAC address in the
Marvell driver, remove the .set_addr implementation of mv88e6xxx and
dsa_loop, and finally remove this code from DSA core completely.


Thanks,

        Vivien