netdev - Re: [patch net-next RFC 00/10] introduce line card support for modular switch

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Date:   Thu, 21 Jan 2021 09:38:40 -0700
From:   David Ahern <dsahern@...il.com>
To:     Jiri Pirko <jiri@...nulli.us>, Jakub Kicinski <kuba@...nel.org>
Cc:     Andrew Lunn <andrew@...n.ch>, netdev@...r.kernel.org,
        davem@...emloft.net, jacob.e.keller@...el.com, roopa@...dia.com,
        mlxsw@...dia.com
Subject: Re: [patch net-next RFC 00/10] introduce line card support for
 modular switch

On 1/21/21 8:32 AM, Jiri Pirko wrote:
> Thu, Jan 21, 2021 at 12:41:58AM CET, kuba@...nel.org wrote:
>> On Wed, 20 Jan 2021 14:56:46 +0100 Andrew Lunn wrote:
>>>> No, the FW does not know. The ASIC is not physically able to get the
>>>> linecard type. Yes, it is odd, I agree. The linecard type is known to
>>>> the driver which operates on i2c. This driver takes care of power
>>>> management of the linecard, among other tasks.  
>>>
>>> So what does activated actually mean for your hardware? It seems to
>>> mean something like: Some random card has been plugged in, we have no
>>> idea what, but it has power, and we have enabled the MACs as
>>> provisioned, which if you are lucky might match the hardware?
>>>
>>> The foundations of this feature seems dubious.
>>
>> But Jiri also says "The linecard type is known to the driver which
>> operates on i2c." which sounds like there is some i2c driver (in user
>> space?) which talks to the card and _does_ have the info? Maybe I'm
>> misreading it. What's the i2c driver?
> 
> That is Vadim's i2c kernel driver, this is going to upstream.
> 

This pre-provisioning concept makes a fragile design to work around h/w
shortcomings. You really need a way for the management card to know
exactly what was plugged in to a slot so the control plane S/W can
respond accordingly. Surely there is a way for processes on the LC to
communicate with a process on the management card - even if it is inband
packets with special headers.