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

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Message-ID: <20210120161637.6735ef4a@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Wed, 20 Jan 2021 16:16:37 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Jiri Pirko <jiri@...nulli.us>, 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 Thu, 21 Jan 2021 01:01:21 +0100 Andrew Lunn 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...

I see that does make sense 🤔