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Date:   Sat, 1 Feb 2020 09:36:20 -0800
From:   Jakub Kicinski <kuba@kernel.org>
To:     Russell King - ARM Linux admin <linux@armlinux.org.uk>
Cc:     Jiri Pirko <jiri@mellanox.com>, Andrew Lunn <andrew@lunn.ch>,
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Subject: Re: [EXT] Re: [PATCH] bus: fsl-mc: Add ACPI support for fsl-mc
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On Sat, 1 Feb 2020 11:49:19 +0000, Russell King - ARM Linux admin wrote:
> What if someone decides to do:
> 
> 	devlink port split device/1 count 2
> 
> what do we end up with?  Presumably two network devices running with
> two serdes lanes each (if supported by the hardware).  At that point
> can they then do:
> 
> 	devlink port split device/2 count 2
> 
> and end up with one network device with two 10G serdes lanes, and two
> network devices each with one 10G serdes lane, 

I think all your guesses are correct, it's a pretty straight forward
API, but it's also pretty thin, and some of the logic is in FW, so
there isn't much in a way of a standard on how things should behave :S

> or can port splitting only be used on the "master" device/port ?

I think both mlxsw and the NFP rejects re-split/further splitting.
Ports have to be unsplit first. So there is only one device for
splitting, and unsplitting can be done on any of the sub-devices.

> Unfortunately, I don't think I have any network devices that support
> this so I can't experiment to find out how this should work; yes, I
> have a Mellanox card, but it supports a single 10G SFP+, and therefore
> does not support port splitting.

I think you'd need a mlxsw or an nfp to play with this.

Maybe Jiri can clarify further :)