linux-kernel - RE: [EXT] Re: [V2 net-next] net: mvpp2: Add reserved port private flag configuration

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Date:   Mon, 22 Mar 2021 15:59:43 +0000
From:   Stefan Chulski <stefanc@...vell.com>
To:     Andrew Lunn <andrew@...n.ch>
CC:     "kuba@...nel.org" <kuba@...nel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "thomas.petazzoni@...tlin.com" <thomas.petazzoni@...tlin.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        Nadav Haklai <nadavh@...vell.com>,
        Yan Markman <ymarkman@...vell.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux@...linux.org.uk" <linux@...linux.org.uk>,
        "mw@...ihalf.com" <mw@...ihalf.com>,
        "rmk+kernel@...linux.org.uk" <rmk+kernel@...linux.org.uk>,
        "atenart@...nel.org" <atenart@...nel.org>,
        "rabeeh@...id-run.com" <rabeeh@...id-run.com>
Subject: RE: [EXT] Re: [V2 net-next] net: mvpp2: Add reserved port private
 flag configuration


> > 2. CM3 code has very small footprint requirement, we cannot 
> > implement the complete Serdes and PHY infrastructure that kernel 
> > provides as part of CM3 application. Therefore I would like to 
> > continue relying on kernel configuration for that.
> 
> How can that work? How does Linux know when CM3 has up'ed the 
> interface?

CM3 won't use this interface till ethtool priv flag was set, it can be done by communication over CM3 SRAM memory.

> How does CM3 know the status of the link?

CM3 has access to MAC registers and can read port status bit.

> How does CM3 set its
> flow control depending on what auto-neg determines, etc?

Same as PPv2 Packet Processor RX and TX flow don't really care about auto-neg, flow control, etc.
CM3 can ignore it, all this stuff handled in MAC layer. CM3 just polling RX descriptor ring and using TX ring for transmit. 

> 
> > 3. In some cases we need to dynamically switch the port "user"
> > between CM3 and kernel. So I would like to preserve this 
> > functionality.
> 
> And how do you synchronize between Linux and CM3 so you know how is 
> using it and who cannot use it?
> 
>       Andrew

I can add CM3 SRAM update into ethtool priv flag callback, so CM3 won't use port till it was reserved to CM3.

Stefan.