netdev - Re: [RFC v2, net-next, PATCH 4/4] net/cpsw_switchdev: add switchdev mode of operation on cpsw driver

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Date:   Thu, 21 Jun 2018 14:19:55 +0200
From:   Ivan Vecera <ivecera@...hat.com>
To:     Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Florian Fainelli <f.fainelli@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>, netdev@...r.kernel.org,
        grygorii.strashko@...com, ivan.khoronzhuk@...aro.org,
        nsekhar@...com, jiri@...nulli.us, francois.ozog@...aro.org,
        yogeshs@...com, spatton@...com, Jose.Abreu@...opsys.com
Subject: Re: [RFC v2, net-next, PATCH 4/4] net/cpsw_switchdev: add switchdev
 mode of operation on cpsw driver

On 20.6.2018 20:03, Ilias Apalodimas wrote:
> Hi Florian,
> 
> On Wed, Jun 20, 2018 at 10:58:26AM -0700, Florian Fainelli wrote:
>> On 06/20/2018 10:51 AM, Ilias Apalodimas wrote:
>>> Hello Ivan,
>>> On Wed, Jun 20, 2018 at 02:56:48PM +0200, Ivan Vecera wrote:
>>>> On 18.6.2018 22:19, Ilias Apalodimas wrote:
>>>>> Jiri proposed using devlink, which makes sense, but i am not sure it's
>>>>> applicable on this patchset. This will change the driver completely and will
>>>>> totally break backwards compatibility.
>>>>
>>>> Another good reason for a new driver.
>>>>
>>>> I.
>>> This is actually conflicting at least to my understanding. Jiri proposed using 
>>> devlink was used as an alternative method to enable a new mode instead of 
>>> adding it on a .config option. A new driver wouldn't have a need for that right?
>>
>> Correct, with a new driver would likely behave correctly upon being
>> probed such that you could have your switch ports act as normal network
>> devices from which you could run IP-config and do NFS boot.
> The current driver also does NFS properly and the 2 ethernet ports act as normal
> network interfaces. The NFS section in the cover letter
> is to cover the cases were users running on NFS need to change the running
> switch configuration(starting from adding the 2 interfaces on a bridge). 
> Since iproute2 is located on the NFS filesystem the moment
> network connectivity is lost, you loose the ability to perform further
> configuration and in certian configuration scenarios render the device
> unusable.

Yes, with a new driver you can drop NFS-boot hack you mentioned in cover letter.
All configuration is done during driver probe and thus prior NFS mount. Only
thing you loose with a new driver is backward compatibility but the question is:
DO you really need it?

Ivan