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

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Date:   Thu, 21 Jan 2021 16:34:10 +0100
From:   Jiri Pirko <jiri@...nulli.us>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Jakub Kicinski <kuba@...nel.org>, 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

Thu, Jan 21, 2021 at 01:01:21AM CET, andrew@...n.ch wrote:
>On Wed, Jan 20, 2021 at 03:41:58PM -0800, Jakub Kicinski 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?
>
>Hi Jakub
>
>A complete guess, but i think it will be the BMC, not the ASIC. There
>have been patches from Mellanox in the past for a BMC, i think sent to
>arm-soc, for the ASPEED devices often used as BMCs. And the BMC is
>often the device doing power management. So what might be missing is
>an interface between the driver and the BMC. But that then makes the
>driver system specific. A OEM who buys ASICs and makes their own board
>could have their own BMC running there own BMC firmware.
>
>All speculation...

Basically all correct.

The thing is mlxsw and the i2c driver cannot talk to each other:
1) It would be ugly
2) They may likely be on a different host


>
>      Andrew