linux-kernel - Re: [PATCH v2 1/3] net: stmmac: allow drivers to explicitly select PHY device

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Message-ID: <CADvTj4qRmjUQJnhamkWNpHGNAtvFyOJnbaQ5RZ6NYYqSNhxshA@mail.gmail.com>
Date: Tue, 27 May 2025 14:16:26 -0600
From: James Hilliard <james.hilliard1@...il.com>
To: Andrew Lunn <andrew@...n.ch>
Cc: netdev@...r.kernel.org, linux-sunxi@...ts.linux.dev, 
	Andrew Lunn <andrew+netdev@...n.ch>, "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>, Alexandre Torgue <alexandre.torgue@...s.st.com>, 
	Russell King <linux@...linux.org.uk>, 
	"Russell King (Oracle)" <rmk+kernel@...linux.org.uk>, Furong Xu <0x1207@...il.com>, 
	Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>, linux-stm32@...md-mailman.stormreply.com, 
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/3] net: stmmac: allow drivers to explicitly select
 PHY device

On Tue, May 27, 2025 at 2:02 PM Andrew Lunn <andrew@...n.ch> wrote:
>
> On Tue, May 27, 2025 at 01:21:21PM -0600, James Hilliard wrote:
> > On Tue, May 27, 2025 at 1:14 PM Andrew Lunn <andrew@...n.ch> wrote:
> > >
> > > On Tue, May 27, 2025 at 11:55:54AM -0600, James Hilliard wrote:
> > > > Some devices like the Allwinner H616 need the ability to select a phy
> > > > in cases where multiple PHY's may be present in a device tree due to
> > > > needing the ability to support multiple SoC variants with runtime
> > > > PHY selection.
> > >
> > > I'm not convinced about this yet. As far as i see, it is different
> > > variants of the H616. They should have different compatibles, since
> > > they are not actually compatible, and you should have different DT
> > > descriptions. So you don't need runtime PHY selection.
> >
> > Different compatibles for what specifically? I mean the PHY compatibles
> > are just the generic "ethernet-phy-ieee802.3-c22" compatibles.
>
> You at least have a different MTD devices, exporting different
> clocks/PWM/Reset controllers.

I assume you mean MFD not MTD devices here.

> That should have different compatibles,
> since they are not compatible.

I agree with that for the MFD devices, but we still need a way
to choose the correct one at runtime otherwise initialization
won't succeed AFAIU.

> You then need phandles to these
> different clocks/PWM/Reset controllers, and for one of the PHYs you
> need a phandle to the I2C bus, so the PHY driver can do the
> initialisation.

Well this would be an indirect reference to the i2c bus right?
I mean the phy would reference a reset controller which would
in turn reference the I2C bus right?

> So i think in the end you know what PHY you have on
> the board, so there is no need to do runtime detection.

But we still need to somehow runtime select the correct phy
which in turn references the phandle to the correct reset
controller right?

> What you might want however is to validate the MTD device compatible
> against the fuse and return -ENODEV if the compatible is wrong for the
> fuse.

Sure, that may make sense to do as well, but I still don't see
how that impacts the need to runtime select the PHY which
is configured for the correct MFD.