linux-kernel - Re: [PATCH net-next v3] net: marvell: prestera: add firmware v4.0 support

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Date:   Fri, 22 Oct 2021 22:27:01 +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 v3] net: marvell: prestera: add firmware v4.0
 support

> On Wed, Oct 20, 2021 at 12:32:28PM +0300, Volodymyr Mytnyk wrote:
> > From: Volodymyr Mytnyk <vmytnyk@...vell.com>
> > 
> > Add firmware (FW) version 4.0 support for Marvell Prestera
> > driver.
> > 
> > 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 driver vesrions.
> > 
> > Current v4.0 FW feature set support does not expect any changes
> > to ABI, as it was defined and tested through long period of time.
> > The ABI may be extended in case of new features, but it will not
> > break the backward compatibility.
> > 
> > ABI major changes done in v4.0:
> > - L1 ABI, where MAC and PHY API configuration are split.
> > - ACL has been split to low-level TCAM and Counters ABI
> >   to provide more HW ACL capabilities for future driver
> >   versions.
> > 
> > To support backward support, the addition compatibility 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 anyway, So, the idea was to break backward support
> > and focus on more stable FW instead of supporting old version
> > with very minimal and limited set of features/capabilities.
>  
> > +/* TODO: add another parameters here: modes, etc... */
> > +struct prestera_port_phy_config {
> > +     bool admin;
> > +     u32 mode;
> > +     u8 mdix;
> > +};
> 
> > @@ -242,10 +246,44 @@ union prestera_msg_port_param {
> >        u8  duplex;
> >        u8  fec;
> >        u8  fc;
> > -     struct prestera_msg_port_mdix_param mdix;
> > -     struct prestera_msg_port_autoneg_param autoneg;
> > +
> > +     union {
> > +             struct {
> > +                     /* TODO: merge it with "mode" */
> 
> > +             struct {
> > +                     /* TODO: merge it with "mode" */
> > +                     u8 admin:1;
> > +                     u8 adv_enable;
> > +                     u64 modes;
> > +                     /* TODO: merge it with modes */
> > +                     u32 mode;
> > +                     u8 mdix;
> > +             } phy;
> 
> You claim this is stable, yet there are four TODOs. Please could you
> convince us you can actually do these TODO without breaking the
> ABI. Can you add more members to the end of these structures, and the
> firmware/driver can know they are there? Since these are often unions,
> you might not be able to tell from the length of the message
> exchanged.

Those TODOs are not valid anymore, will just remove the comments. No merge
is needed :) Adding new members to the end will be fine for the firmware
& driver.

> 
> As Jakub pointed out, your structures have horrible alignment. Have
> you run this on both 32 and 64 bit systems? It would be good to add
> 
> BUILD_BUG_ON(sizeof(*foo) != 42)
> 
> for all the structures that get passed to/from the firmware.
> 
>     Andrew

Most of the testing is done on 64 bit system. On 32 should be fine also, as
the structure is packed & aligned. Anyway, I think to add build checking is
good idea to make sure the size is fine on both systems. Thanks.

  Volodymyr