linux-kernel - Re: [PATCH net-next v2 10/10] net: stmmac: Add DW XPCS specified via "pcs-handle" support

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Date: Tue, 4 Jun 2024 12:04:57 +0300
From: Serge Semin <fancer.lancer@...il.com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: Andrew Lunn <andrew@...n.ch>, Heiner Kallweit <hkallweit1@...il.com>, 
	Alexandre Torgue <alexandre.torgue@...s.st.com>, Jose Abreu <joabreu@...opsys.com>, 
	Jose Abreu <Jose.Abreu@...opsys.com>, Vladimir Oltean <olteanv@...il.com>, 
	Florian Fainelli <f.fainelli@...il.com>, Maxime Chevallier <maxime.chevallier@...tlin.com>, 
	Rob Herring <robh+dt@...nel.org>, Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, 
	Conor Dooley <conor+dt@...nel.org>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, Maxime Coquelin <mcoquelin.stm32@...il.com>, 
	Sagar Cheluvegowda <quic_scheluve@...cinc.com>, Abhishek Chauhan <quic_abchauha@...cinc.com>, 
	Andrew Halaney <ahalaney@...hat.com>, Jiawen Wu <jiawenwu@...stnetic.com>, 
	Mengyuan Lou <mengyuanlou@...-swift.com>, Tomer Maimon <tmaimon77@...il.com>, openbmc@...ts.ozlabs.org, 
	netdev@...r.kernel.org, devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-stm32@...md-mailman.stormreply.com, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH net-next v2 10/10] net: stmmac: Add DW XPCS specified via
 "pcs-handle" support

On Mon, Jun 03, 2024 at 10:03:54AM +0100, Russell King (Oracle) wrote:
> On Mon, Jun 03, 2024 at 11:54:22AM +0300, Serge Semin wrote:
> > >  	if (priv->plat->pcs_init) {
> > >  		ret = priv->plat->pcs_init(priv);
> > 
> > > +	} else if (fwnode_property_present(devnode, "pcs-handle")) {
> > > +		pcsnode = fwnode_find_reference(devnode, "pcs-handle", 0);
> > > +		xpcs = xpcs_create_fwnode(pcsnode, mode);
> > > +		fwnode_handle_put(pcsnode);
> > > +		ret = PTR_ERR_OR_ZERO(xpcs);
> > 
> > Just figured, we might wish to be a bit more portable in the
> > "pcs-handle" property semantics implementation seeing there can be at
> > least three different PCS attached:
> > DW XPCS
> > Lynx PCS
> > Renesas RZ/N1 MII
> > 
> > Any suggestion of how to distinguish the passed handle? Perhaps
> > named-property, phandle argument, by the compatible string or the
> > node-name?
> 

> I can't think of a reasonable solution to this at the moment. One
> solution could be pushing this down into the platform code to deal
> with as an interim solution, via the new .pcs_init() method.
> 
> We could also do that with the current XPCS code, since we know that
> only Intel mGBE uses xpcs. This would probably allow us to get rid
> of the has_xpcs flag.

Basically you suggest to move the entire stmmac_pcs_setup() to the
platforms, don't you? The patch 9 of this series indeed could have
been converted to just moving the entire PCS-detection loop from
stmmac_pcs_setup() to the Intel-specific pcs_init.

But IMO some default/generic code would be still useful to preserve in
the stmmac_pcs_setup() method. When it comes to the fwnode-based
platform we at least could be falling back to the default DW XPCS
device registration if no plat_stmmacenet_data::pcs_init() callback
was specified and there was the "pcs-handle" property found,
especially seeing DW *MAC and DW XPCS are of the same vendor.

Based on that I can convert patch 9 of this series to introducing the
pcs_init() callback in the Intel mGBE driver, but preserve the
semantics of the rest of the series changes.

-Serge(y)

> 
> -- 
> RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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