linux-kernel - Re: [PATCH net-next v2] net: marvell: prestera: add firmware v4.0 support

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Message-ID: <SJ0PR18MB40099BBA546BFBE941B969DCB2BD9@SJ0PR18MB4009.namprd18.prod.outlook.com>
Date:   Tue, 19 Oct 2021 16:01:09 +0000
From:   "Volodymyr Mytnyk [C]" <vmytnyk@...vell.com>
To:     Andrew Lunn <andrew@...n.ch>
CC:     "kuba@...nel.org" <kuba@...nel.org>,
        Mickey Rachamim <mickeyr@...vell.com>,
        Serhiy Pshyk <serhiy.pshyk@...ision.eu>,
        Taras Chornyi <taras.chornyi@...ision.eu>,
        "Vadym Kochan [C]" <vkochan@...vell.com>,
        Yevhen Orlov <yevhen.orlov@...ision.eu>,
        "Taras Chornyi [C]" <tchornyi@...vell.com>,
        "David S. Miller" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next v2] net: marvell: prestera: add firmware v4.0
 support

Hi Andrew,

> On Tue, Oct 19, 2021 at 09:03:43AM +0300, Volodymyr Mytnyk wrote:
> > From: Volodymyr Mytnyk <vmytnyk@...vell.com>
> >
> > Add firmware (FW) version 4.0 support for Marvell Prestera
> > driver. This FW ABI will be compatible with future Prestera
> > driver versions and features.
> >
> > The previous FW support is dropped due to significant changes
> > in FW ABI, thus this version of Prestera driver will not be
> > compatible with previous FW versions.
> 
> So we are back to breaking any switch already deployed using the
> driver with the older firmware. Bricks in broom closets, needing
> physical access to fix them. Was nothing learnt from the upgrade from
> v2 to v3 with its ABI breakage and keeping backwards support for one
> version? Do you see other vendors making ABI breaking changes to there
> firmware?

- Major changes have been made to new v4.0 FW ABI to add support of new features,
  introduce the stability of the FW ABI and ensure better forward compatibility
  for the future vesrions. So, the idea was to break support and focus on more
  stable FW instead of supporting old version with very minimal and limited set
  of features/capabilities.

- For backward support, the addition compatability layer is required in the 
  driver which will have two different codebase under "if FW-VER elif FW-VER else"
  conditions that will be removed in the future.

- All current platforms using this driver have dedicated OOB mgmt port, thus the
  user still be able to do upgrade of the FW. So, no "Bricks in broom closets" :).
  Also, this is Marvell guidelines to have OOB for the future platforms.

> 
> Why would anybody decide to use Marvell, when you can use Microchip
> devices an avoid all these problems?
> 
>         Andrew
>

Volodymyr