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

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Date:   Wed, 29 Apr 2020 01:39:15 +0000
From:   Andy Duan <fugang.duan@....com>
To:     Andrew Lunn <andrew@...n.ch>
CC:     netdev <netdev@...r.kernel.org>, Chris Healy <cphealy@...il.com>,
        Leonard Crestez <leonard.crestez@....com>
Subject: RE: [EXT] Re: [PATCH net-next] net: ethernet: fec: Prevent MII event
 after MII_SPEED write

From: Andrew Lunn <andrew@...n.ch> Sent: Wednesday, April 29, 2020 2:02 AM
> 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

Yes, we need to wait for linux next.

Andy