netdev - Re: [PATCH net-next v3 02/11] net: phy: introduce phy_has_c45

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Date: Thu, 3 Aug 2023 00:21:03 +0200
From: Andrew Lunn <andrew@...n.ch>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: Michael Walle <mwalle@...nel.org>,
	Heiner Kallweit <hkallweit1@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Yisen Zhuang <yisen.zhuang@...wei.com>,
	Salil Mehta <salil.mehta@...wei.com>,
	Florian Fainelli <florian.fainelli@...adcom.com>,
	Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>,
	Marek Behún <kabel@...nel.org>,
	Xu Liang <lxu@...linear.com>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Simon Horman <simon.horman@...igine.com>
Subject: Re: [PATCH net-next v3 02/11] net: phy: introduce
 phy_has_c45_registers()

On Wed, Aug 02, 2023 at 06:10:27PM +0100, Russell King (Oracle) wrote:
> On Wed, Aug 02, 2023 at 06:15:19PM +0200, Andrew Lunn wrote:
> > > I'm confused now. Andrew suggested to split it into four different
> > > functions:
> > > 
> > > phy_has_c22_registers()
> > > phy_has_c45_registers()
> > > phy_has_c22_transfers()
> > > phy_has_c45_transfers()
> > > 
> > > Without a functional change. That is, either return phydev->is_c45
> > > or the inverse.
> > 
> > Without a functional change at this step of introducing the four
> > functions. Then later really implement them to do what the name
> > implies. Doing it in steps helps with bisect when it breaks something.
> > 
> > It could also be that not all four are needed, or not all four are
> > possible. But the four express the full combinations of transfers and
> > registers.
> 
> I'm left wondering how you think that phy_has_c45_registers() can
> be implemented in a useful way, because I'm at a total loss...

get_phy_c22_id() looks at the ID registers, and see if its mostly
Fs. If so, it says -ENODEV. So phy_has_c22_registers() could be
get_phy_c22_id() != -ENODEV. And you can extend that with the logic
you quoted from the standard. get_phy_c45_ids() also returns -ENODEV
if there are no devices in the package. So phy_has_c45_registers()
could be get_phy_c45_id() != -ENODEV.

This is heuristics, not something explicitly from the standard, but
the basic idea of looking for not mostly Fs has been used for a long
time.

    Andrew