Re: [PATCH net-next v2 00/11] net: pcs: Add support for devices probed in the "usual" manner

From: Vladimir Oltean <vladimir.oltean@nxp.com>
To: Andrew Lunn <andrew@lunn.ch>
Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>,
	Madalin Bucur <madalin.bucur@nxp.com>,
	Eric Dumazet <edumazet@google.com>,
	Paul Mackerras <paulus@samba.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Ioana Ciornei <ioana.ciornei@nxp.com>,
	"UNGLinuxDriver@microchip.com" <UNGLinuxDriver@microchip.com>,
	Frank Rowand <frowand.list@gmail.com>,
	Florian Fainelli <f.fainelli@gmail.com>,
	Saravana Kannan <saravanak@google.com>,
	Sean Anderson <sean.anderson@seco.com>,
	Russell King <linux@armlinux.org.uk>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	Vivien Didelot <vivien.didelot@gmail.com>,
	"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
	"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
	Claudiu Manoil <claudiu.manoil@nxp.com>,
	Rob Herring <robh+dt@kernel.org>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux -kernel@vger.kernel.org>,
	Leo Li <leoyang.li@nxp.com>, Vladimir Oltean <olteanv@gmail.com>,
	Shawn Guo <shawnguo@kernel.org>,
	"David S . Miller" <davem@davemloft.net>,
	Heiner Kallweit <hkallweit1@gmail.com>
Subject: Re: [PATCH net-next v2 00/11] net: pcs: Add support for devices probed in the "usual" manner
Date: Thu, 10 Nov 2022 16:32:38 +0000	[thread overview]
Message-ID: <20221110163237.vigulusm2c5bepp3@skbuf> (raw)
In-Reply-To: <Y20gXppMemnHSTG9@lunn.ch>

On Thu, Nov 10, 2022 at 05:01:34PM +0100, Andrew Lunn wrote:
> On Thu, Nov 10, 2022 at 03:29:26PM +0000, Vladimir Oltean wrote:
> > On Thu, Nov 10, 2022 at 09:55:32AM -0500, Sean Anderson wrote:
> > > On 11/9/22 17:41, Vladimir Oltean wrote:
> > > > On Thu, Nov 03, 2022 at 05:06:39PM -0400, Sean Anderson wrote:
> > > >> Several (later) patches in this series cannot be applied until a stable
> > > >> release has occured containing the dts updates.
> > > > 
> > > > New kernels must remain compatible with old device trees.
> > > 
> > > Well, this binding is not present in older device trees, so it needs to
> > > be added before these patches can be applied. It also could be possible
> > > to manually bind the driver using e.g. a helper function (like what is
> > > done with lynx_pcs_create_on_bus). Of course this would be tricky,
> > > because we would need to unbind any generic phy driver attached, but
> > > avoid unbinding an existing Lynx PCS driver.
> > 
> > If you know the value of the MII_PHYSID1 and MII_PHYSID2 registers for
> > these PCS devices, would it be possible to probe them in a generic way
> > as MDIO devices, if they lack a compatible string?
> 
> That is not how it currently works. If a device on an MDIO bus has a
> compatible, it is assumed to be an mdio device, and it is probed in a
> generic way as an sort of mdio device. It could be an Ethernet switch,
> or Broadcom has some generic PHYs which are mdio devices, etc.
> 
> If there is no compatible, the ID registers are read and it is assumed
> to be a PHY. It will be probed as a PHY. The probe() function will be
> given a phydev etc.
> 
> It will need some core changes to allow an mdio device to be probed
> via the ID registers.

Yes, it would require extending struct mdio_driver with something like
what struct phy_driver has (u32 phy_id, u32 phy_id_mask), or with a more
generic phy_id_match_table (similar to maybe of_match_table).

I don't see a conceptually simpler way though.