netdev - Re: [patch net-next 6/9] mlxsw: spectrum: Unmap local port from module during teardown

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Date:	Mon, 22 Feb 2016 23:00:54 +0200
From:	Ido Schimmel <idosch@...lanox.com>
To:	John Fastabend <john.fastabend@...il.com>
CC:	Jiri Pirko <jiri@...nulli.us>, <netdev@...r.kernel.org>,
	<davem@...emloft.net>, <eladr@...lanox.com>, <yotamg@...lanox.com>,
	<ogerlitz@...lanox.com>, <yishaih@...lanox.com>,
	<dledford@...hat.com>, <sean.hefty@...el.com>,
	<hal.rosenstock@...il.com>, <eugenia@...lanox.com>,
	<roopa@...ulusnetworks.com>, <nikolay@...ulusnetworks.com>,
	<hadarh@...lanox.com>, <jhs@...atatu.com>,
	<jeffrey.t.kirsher@...el.com>, <brouer@...hat.com>,
	<ivecera@...hat.com>, <rami.rosen@...el.com>
Subject: Re: [patch net-next 6/9] mlxsw: spectrum: Unmap local port from
 module during teardown

Hi John,

Mon, Feb 22, 2016 at 10:32:47PM IST, john.fastabend@...il.com wrote:
>On 16-02-22 10:32 AM, Jiri Pirko wrote:
>> From: Ido Schimmel <idosch@...lanox.com>
>> 
>> When splitting a port we replace it with 2 or 4 other ports. To be able
>> to do that we need to remove the original port netdev and unmap it from
>> its module. However, we first mark it as disabled, as active ports
>> cannot be unmapped.
>> 
>> Signed-off-by: Ido Schimmel <idosch@...lanox.com>
>> Signed-off-by: Jiri Pirko <jiri@...lanox.com>
>> ---
>
>Hi Jiri, Ido,
>
>You've sort of lost me on this port splitting/unsplitting thread. What
>does this actually do? Are you just creating two netdevs and LAGing them
>in the hardware, I'm guessing not or you wouldn't have some device API
>for it and would do it using normal methods.

Yep, it's not LAG. You basically have a mapping between a physical
module and a local port, which is represented by a port netdev.

Each module has 4 lanes, so if you connect a splitter (say a 2x) you can
map each 2 lanes to a different port and assign each a new local port.
These are completely independent from each other, but they can only give
you 50Gb/s max, as opposed to the original 100Gb/s (as it had 4 lanes
all to itself).

>
>If its something to do with physical layout of the board itself why
>don't you trigger this based on some init time introspection or an
>interrupt if someone plugs in a port splitting cable/module (does that
>exist?).

We currently don't have an event that tells us that a splitter is
connected. Also, had we created / destroyed these based on events, then
an accidental removal of the splitter would cause all the configuration
setup on these ports to disappear (say VLANs on a bridged port, unicast
flooding etc.).

Thanks.

>
>Thanks,
>John
>
>