netdev - Re: [PATCH] net: axiemac: use a phandle to reference pcs

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Date:   Wed, 16 Mar 2022 21:14:55 +0000
From:   Robert Hancock <robert.hancock@...ian.com>
To:     "andy.chiu@...ive.com" <andy.chiu@...ive.com>
CC:     "linux@...linux.org.uk" <linux@...linux.org.uk>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "michal.simek@...inx.com" <michal.simek@...inx.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "andrew@...n.ch" <andrew@...n.ch>,
        "greentime.hu@...ive.com" <greentime.hu@...ive.com>
Subject: Re: [PATCH] net: axiemac: use a phandle to reference pcs_phy

Re: https://lore.kernel.org/all/20220316075953.61398-1-andy.chiu@sifive.com/
(looks like I was CCed with the wrong email):

I think we likely need something similar to this for the use case (I assume)
you have, where there's an external SGMII PHY as well as the internal PCS/PMA
PHY which both need to be configured. However, we (and possibly others) already
have some cases where the core is connected to an SFP cage, phy-handle points
to the internal PCS/PMA PHY, and the external PHY - if one exists at all - is
not in the device tree because it would be on an SFP module.

Also, as Jakub mentioned, it looks like other drivers like dpaa2 use pcs-handle 
for this.

Possibly something like: in the 1000Base-X or SGMII modes, if pcs-handle is
set, then use that as the PCS node, otherwise fall back to assuming phy-handle
points to the PCS. It should not require that both are present, since even in
the pure SGMII case, the PHY could still be supplied by an SFP module
downstream.

-- 
Robert Hancock
Senior Hardware Designer, Calian Advanced Technologies
www.calian.com