netdev - Re: [PATCH net-next 3/3] selftests: net: Add port split test

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Date:   Tue, 19 May 2020 16:15:41 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Ido Schimmel <idosch@...sch.org>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, kuba@...nel.org,
        jiri@...lanox.com, danieller@...lanox.com, mlxsw@...lanox.com,
        michael.chan@...adcom.com, jeffrey.t.kirsher@...el.com,
        saeedm@...lanox.com, leon@...nel.org, snelson@...sando.io,
        drivers@...sando.io, vivien.didelot@...il.com,
        f.fainelli@...il.com, Ido Schimmel <idosch@...lanox.com>
Subject: Re: [PATCH net-next 3/3] selftests: net: Add port split test

> +# Test port split configuration using devlink-port width attribute.
> +# The test is skipped in case the attribute is not available.
> +#
> +# First, check that all the ports with a width of 1 fail to split.
> +# Second, check that all the ports with a width larger than 1 can be split
> +# to all valid configurations (e.g., split to 2, split to 4 etc.)

Hi Ido

I know very little about splitting ports. So these might be dumb
questions.

Is there a well defined meaning of width? Is it something which can be
found in an 802.3 standard?

Is it well defined that all splits of the for 2, 4, 8 have to be
supported? Must all 40Gbps ports with a width of 4, be splitable to 2x
20Mps? It seems like some hardware might only allow 4x 10G?

If 20Gbps is supported, can you then go recursive and split one of the
20G ports into 2x 10G, leaving the other as a 20G port?

	Andrew