netdev - Re: [PATCH net-next 2/2] net: phy: add keep_data

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Date: Wed, 26 Jul 2023 18:43:01 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Jakub Kicinski <kuba@...nel.org>
Cc: "mengyuanlou@...-swift.com" <mengyuanlou@...-swift.com>,
	"Russell King (Oracle)" <linux@...linux.org.uk>,
	Simon Horman <simon.horman@...igine.com>, netdev@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>,
	Paolo Abeni <pabeni@...hat.com>, Eric Dumazet <edumazet@...gle.com>,
	Heiner Kallweit <hkallweit1@...il.com>
Subject: Re: [PATCH net-next 2/2] net: phy: add keep_data_connection to
 struct phydev

On Wed, Jul 26, 2023 at 09:08:12AM -0700, Jakub Kicinski wrote:
> Sorry for chiming in, hopefully the comments are helpful..

Thanks for commenting. This is a somewhat unusual setup, a server
style Ethernet interface which Linux is driving, not firmware. So its
more like an embedded SoC setup, but has NCSI which embedded systems
don't.

> On Wed, 26 Jul 2023 10:54:25 +0200 Andrew Lunn wrote:
> > As far as i understand it, the host MAC is actually a switch, with the
> > BMC connected to the second port of the switch.
> 
> Not a learning switch (usually, sigh), but yes.
> 
> > Does the BMC care about the PHY status?
> > Does it need to know about link status? 
> 
> Yes, NIC sends link state notifications over the NCSI "link?" (which 
> is a separate RGMII?/RMII from NIC to the BMC). BMC can select which
> "channel" (NIC port) it uses based on PHY status.

How do you define NIC when Linux is driving the hardware, not
firmware? In this case we have a MAC driver, a PCS driver, a PHY
driver and phylink gluing it all together. Which part of this is
sending link state notifications over the NCSI "Link?".

> > Does the NCSI core on the host need to know about the PHY?
> 
> There is no NCSI core on the host.. Hosts are currently completely
> oblivious to NCSI. The NCSI we have in tree is for the BMC, Linux
> running on the BMC (e.g. OpenBMC).

But in this case, it is not oblivious to NCSI, since the host is
controlling the PHY. This patch is about Linux on the host not
shutting down the PHY because it is also being used by the BMC.

	 Andrew