netdev - Re: FEC MDIO read timeout on linkup

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Date:   Mon, 2 May 2022 20:24:53 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Francesco Dolcini <francesco.dolcini@...adex.com>
Cc:     netdev@...r.kernel.org, Andy Duan <fugang.duan@....com>,
        Joakim Zhang <qiangqing.zhang@....com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Fabio Estevam <festevam@...il.com>,
        Tim Harvey <tharvey@...eworks.com>,
        Chris Healy <cphealy@...il.com>
Subject: Re: FEC MDIO read timeout on linkup

> writing to this register could trigger a FEC_ENET_MII interrupt actually
> creating a race condition with fec_enet_mdio_read() that is called on
> link change also.

Another point to consider:

static int fec_enet_mdio_wait(struct fec_enet_private *fep)
{
        uint ievent;
        int ret;

        ret = readl_poll_timeout_atomic(fep->hwp + FEC_IEVENT, ievent,
                                        ievent & FEC_ENET_MII, 2, 30000);

        if (!ret)
                writel(FEC_ENET_MII, fep->hwp + FEC_IEVENT);

        return ret;
}

An unexpected interrupt will make this exit too early, and the read
will get invalid data. An unexpected interrupt would not cause a
timeout here, which is what you are reporting.

	Andrew