netdev - Re: [PATCH net-next] net: ethernet: fec: Prevent MII event after MII

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Message-ID: <20200428180144.GA30612@lunn.ch>
Date:   Tue, 28 Apr 2020 20:01:44 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Andy Duan <fugang.duan@....com>
Cc:     netdev <netdev@...r.kernel.org>, Chris Healy <cphealy@...il.com>,
        Andy Duan <fugang.duan@....com>,
        Leonard Crestez <leonard.crestez@....com>
Subject: Re: [PATCH net-next] net: ethernet: fec: Prevent MII event after
 MII_SPEED write

On Tue, Apr 28, 2020 at 07:58:33PM +0200, Andrew Lunn wrote:
> The change to polled IO for MDIO completion assumes that MII events
> are only generated for MDIO transactions. However on some SoCs writing
> to the MII_SPEED register can also trigger an MII event. As a result,
> the next MDIO read has a pending MII event, and immediately reads the
> data registers before it contains useful data. When the read does
> complete, another MII event is posted, which results in the next read
> also going wrong, and the cycle continues.
> 
> By writing 0 to the MII_DATA register before writing to the speed
> register, this MII event for the MII_SPEED is suppressed, and polled
> IO works as expected.

Hi Andy

Could you get your LAVA instances to test this? Or do we need to wait
for it to make its way into net-next?

Thanks
	Andrew