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Date:   Sat, 29 Aug 2020 00:34:05 +0200
From:   Adam Rudziński <>
To:     Andrew Lunn <>
        netdev <>
Subject: Re: drivers/of/of_mdio.c needs a small modification

Hi Andrew.

W dniu 2020-08-29 o 00:28, Andrew Lunn pisze:
> Hi Adam
>> If kernel has to bring up two Ethernet interfaces, the processor has two
>> peripherals with functionality of MACs (in i.MX6ULL these are Fast Ethernet
>> Controllers, FECs), but uses a shared MDIO bus, then the kernel first probes
>> one MAC, enables clock for its PHY, probes MDIO bus tryng to discover _all_
>> PHYs, and then probes the second MAC, and enables clock for its PHY. The
>> result is that the second PHY is still inactive during PHY discovery. Thus,
>> one Ethernet interface is not functional.
> What clock are you talking about? Do you have the FEC feeding a 50MHz
> clock to the PHY? Each FEC providing its own clock to its own PHY? And
> are you saying a PHY without its reference clock does not respond to
> MDIO reads and hence the second PHY does not probe because it has no
> reference clock?
> 	  Andrew

Yes, exactly. In my case the PHYs are LAN8720A, and it works this way.
Maybe this problem is PHY-related.
I also think that my proposition allows to make device tree look better 
and be less confusing, as a side-effect.

Best regards,

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