netdev - Re: [PATCH net-next RFC v1 1/4] net: devlink: Add support for port regions

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Message-ID: <20200921002317.ltl4b4oqow6o6tba@skbuf>
Date:   Mon, 21 Sep 2020 00:23:18 +0000
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Andrew Lunn <andrew@...n.ch>
CC:     netdev <netdev@...r.kernel.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Jakub Kicinski <kuba@...nel.org>, Jiri Pirko <jiri@...dia.com>,
        Chris Healy <cphealy@...il.com>
Subject: Re: [PATCH net-next RFC v1 1/4] net: devlink: Add support for port
 regions

On Mon, Sep 21, 2020 at 02:45:39AM +0300, Vladimir Oltean wrote:
> This looks like a simple enough solution, but am I right that old
> kernels, which ignore this new DEVLINK_ATTR_PORT_INDEX netlink
> attribute, will consequently interpret any devlink command for a port as
> being for a global region? Sure, in the end, that kernel will probably
> fail anyway, due to the region name mismatch. And at the moment there
> isn't any driver that registers a global and a port region with the same
> name. But when that will happen, the user space tools of the future will
> trigger incorrect behavior into the kernel of today, instead of it
> reporting an unsupported operation as it should. Or am I
> misunderstanding?

Thinking about this more, I believe that the only conditions that need
to be avoided are:
- mlx4 should never create a port region called "cr-space" or "fw-health"
- ice should never create a port region called "nvm-flash" or
  "device-caps"
- netdevsim should never create a port region called "dummy"
- mv88e6xxx should never create a port region called "global1",
  "global2" or "atu"

Because these are the only region names supported by kernels that don't
parse DEVLINK_ATTR_PORT_INDEX, I think we don't need to complicate the
solution, and go with DEVLINK_ATTR_PORT_INDEX.

-Vladimir