netdev - Re: [PATCH net-next 2/2] mv88e6131: bonding: implement single device trunking

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Message-ID: <20150306214723.GB582@lunn.ch>
Date:	Fri, 6 Mar 2015 22:47:23 +0100
From:	Andrew Lunn <andrew@...n.ch>
To:	Florian Fainelli <f.fainelli@...il.com>
Cc:	Jonas Johansson <jonasj76@...il.com>, netdev@...r.kernel.org,
	Jonas Johansson <jonas.johansson@...termo.se>,
	Jiri Pirko <jiri@...nulli.us>,
	Scott Feldman <sfeldma@...il.com>
Subject: Re: [PATCH net-next 2/2] mv88e6131: bonding: implement single device
 trunking

Hi Florian

> Most Broadcom switches, either SF2 or roboswitch (b53) have a limit of 2
> trunking groups, without limitations on the number of ports included in
> any of these two groups.

O.K, so maybe we want the basic resource management in the DSA layer,
not the switch drivers.

> The larger question is once we start advertising capabilities, where
> does that stop, right? It would probably be simpler for now to e.g:
> allow 2 trunking groups to be configured, and when trying to configure a
> 3rd one, return -ENOSPC and act upon that to either take the software
> slow path (which is probably not possible) or just return a hard error
> condition.

This is more than a DSA question. It applies to all the hardware
acceleration being discussed at the moment. As you hinted to above, i
suppose we have two different situations:

1) We can fall back to a software slow path.

2) There is no software fallback, we have to error out, and it would
   be nice to have a well defined error code for out of hardware
   resources.

We also should think about how we tell user space we have fallen back
to a slow path. I'm sure users want to know why it works, but works
much slower.

     Andrew
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