netdev - Re: [RFC PATCH] drivers: net: mdio_bus: try indirect clause 45 regs access

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Message-ID: <20200517175820.GB606317@lunn.ch>
Date:   Sun, 17 May 2020 19:58:20 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Baruch Siach <baruch@...s.co.il>
Cc:     Russell King - ARM Linux admin <linux@...linux.org.uk>,
        Florian Fainelli <f.fainelli@...il.com>,
        Heiner Kallweit <hkallweit1@...il.com>, netdev@...r.kernel.org
Subject: Re: [RFC PATCH] drivers: net: mdio_bus: try indirect clause 45 regs
 access

> > I don't think this should be done at mdiobus level; I think this is a
> > layering violation.  It needs to happen at the PHY level because the
> > indirect C45 access via C22 registers is specific to PHYs.
> >
> > It also needs to check in the general case that the PHY does indeed
> > support the C22 register set - not all C45 PHYs do.
> >
> > So, I think we want this fallback to be conditional on:
> >
> > - are we probing for the PHY, trying to read its IDs and
> >   devices-in-package registers - if yes, allow fallback.
> > - does the C45 PHY support the C22 register set - if yes, allow
> >   fallback.
> 
> I'll take a look. Thanks.

Hi Baruch

Another option to consider is a third compatible string. We have
compatibles for C22, C45. Add another one for C45 over C22, and have
the core support it as the third access method next to C22 and C45.

We already rely on the DT author getting C22 vs C45 correct for the
hardware. Is it too much to ask they get it write when there are three
options?

As to your particular hardware, if i remember correctly, some of the
Marvell SoCs have mdio and xmdio bus masters. The mdio bus can only do
C22, and the xmdio can only do C45. Have the hardware engineers put
the PHY on the wrong bus?

     Andrew