netdev - Re: FEC MDIO read timeout on linkup

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Message-ID: <YnAhFse2h0vN1FCM@lunn.ch>
Date:   Mon, 2 May 2022 20:21:10 +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

> Could it be that the issue is writing the MSCR in fec_restart(),
> `writel(fep->phy_speed, fep->hwp + FEC_MII_SPEED)`?
> 
> I do see the issue on link up/down event, when this function is actually
> called.
> 
> >From what I can understand from the previous history:
> 
>   1e6114f51f9d (net: fec: fix MDIO probing for some FEC hardware blocks, 2020-10-28) 
>   f166f890c8f0 (net: ethernet: fec: Replace interrupt driven MDIO with polled IO, 2020-05-02)
> 
> 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.

You should read the discussion from when this code was added.

Are you planning on adding:

       if (fep->quirks & FEC_QUIRK_CLEAR_SETUP_MII) {
                /* Clear MMFR to avoid to generate MII event by writing MSCR.
                 * MII event generation condition:
                 * - writing MSCR:
                 *      - mmfr[31:0]_not_zero & mscr[7:0]_is_zero &
                 *        mscr_reg_data_in[7:0] != 0
                 * - writing MMFR:
                 *      - mscr[7:0]_not_zero
                 */
                writel(0, fep->hwp + FEC_MII_DATA);
        }

To other locations which change FEC_MII_SPEED?

   Andrew