netdev - Re: [PATCH net-next 00/11] mlxsw: extend line card model by devices and info

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Date:   Wed, 1 Jun 2022 09:35:04 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Ido Schimmel <idosch@...sch.org>, Ido Schimmel <idosch@...dia.com>,
        netdev@...r.kernel.org, davem@...emloft.net, pabeni@...hat.com,
        jiri@...dia.com, petrm@...dia.com, dsahern@...il.com,
        andrew@...n.ch, mlxsw@...dia.com
Subject: Re: [PATCH net-next 00/11] mlxsw: extend line card model by devices
 and info

Wed, Jun 01, 2022 at 12:41:59AM CEST, kuba@...nel.org wrote:
>On Tue, 31 May 2022 21:34:42 +0200 Jiri Pirko wrote:
>> And again, for the record, I strongly believe that a separate dl
>> instance for this does not make any sense at all :/ I wonder why you
>> still think it does.
>
>For purely software reuse reasons. I think the line cards will require
>a lot of the same attributes as the full devlink instance, so making
>them a subobject which can have all the same attributes is poor SW arch.

Sure, I understand the motivation.

>Think about it from OOP perspective, you'd definitely factor all that
>stuff out to an abstract class. We can't do that in netlink but whatever
>just make it a full dl instance and describe the link between the two.
>
>Most NIC vendors (everyone excluding Netronome?) decided that devlink
>instance is equivalent to a bus device which IIUC it was not supposed
>to be. It was supposed to be the whole ASIC. If we're okay to stretch

I agree, that is incorrect. That is why I was thinking about sort of
"alias" to make it right (2 PF devlink instances would be one connected
by alias). Not implemented yet though :/

>the definition of a dl instance to be "any independently controllable
>unit of HW" for NICs then IDK why we can't make a line card a dl
>instance.

Well, it is not independently controllable. Well, truth is, that in our
current implementation, there is one independent "configuration", and
that is flash burn of the gearbox. It is done using a "tunnelling"
register which encapsulates register communication what is done during
flash burning.

>
>Are you afraid of hiding dependencies?

Not really, I'm just not sure I see it is worth the excercise.

In czech, we have this saying: "kanon na vrabce". I think that the
following picture is better than any translation :)
https://i.iinfo.cz/images/72/shutterstock-com-kanon-delo-ptak-vrabec-strilet-1.jpg

Will think about it some more.