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

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Message-Id: <20200428.143339.1189475969435668035.davem@davemloft.net>
Date:   Tue, 28 Apr 2020 14:33:39 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     andrew@...n.ch
Cc:     netdev@...r.kernel.org, cphealy@...il.com, fugang.duan@....com,
        leonard.crestez@....com
Subject: Re: [PATCH net-next] net: ethernet: fec: Prevent MII event after
 MII_SPEED write

From: Andrew Lunn <andrew@...n.ch>
Date: Tue, 28 Apr 2020 19:58:33 +0200

> 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.
> 
> Fixes: 29ae6bd1b0d8 ("net: ethernet: fec: Replace interrupt driven MDIO with polled IO")
> Reported-by: Andy Duan <fugang.duan@....com>
> Suggested-by: Andy Duan <fugang.duan@....com>
> Signed-off-by: Andrew Lunn <andrew@...n.ch>

Applied to net-next, thanks.