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

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Message-ID: <87v9ku1kwe.fsf@tarshish>
Date:   Sun, 17 May 2020 21:22:41 +0300
From:   Baruch Siach <baruch@...s.co.il>
To:     Andrew Lunn <andrew@...n.ch>
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

Hi Andrew,

On Sun, May 17 2020, Andrew Lunn wrote:
>> > 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.
>  
> 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?

Networking hardware DT configuration is confusing enough already. Since
we can determine indirect C45 access automatically, I think we should do
that.

> 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?

The Armada 385 has only C22 MDIO. Other Armada SoCs have both MDIO and
XMDIO.

baruch

-- 
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