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

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Message-ID: <b845912e-a65a-6800-82e7-b2d26cd29d4e@gmail.com>
Date:   Thu, 12 Oct 2017 15:43:10 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Vivien Didelot <vivien.didelot@...oirfairelinux.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

On 10/12/2017 03:35 PM, Vivien Didelot wrote:
> 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.

Works for me, thanks!
-- 
Florian