netdev - RE: [EXT] Re: [PATCH] net: ethernet: fec: Replace interrupt driven MDIO with polled IO

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Date:   Thu, 22 Oct 2020 09:04:01 +0000
From:   Andy Duan <fugang.duan@....com>
To:     Greg Ungerer <gerg@...ux-m68k.org>, Andrew Lunn <andrew@...n.ch>,
        Dave Karr <dkarr@...x.com>,
        Clemens Gruber <clemens.gruber@...ruber.com>
CC:     Chris Heally <cphealy@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [EXT] Re: [PATCH] net: ethernet: fec: Replace interrupt driven
 MDIO with polled IO

From: Greg Ungerer <gerg@...ux-m68k.org> Sent: Thursday, October 22, 2020 9:14 AM
> Hi Andrew,
> 
> On 21/10/20 11:37 pm, Andrew Lunn wrote:
> >> +    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);
> >> +    }
> >
> > Hi Greg
> >
> > The last time we discussed this, we decided that if you cannot do the
> > quirk, you need to wait around for an MDIO interrupt, e.g. call
> > fec_enet_mdio_wait() after setting FEC_MII_SPEED register.
> >
> >>
> >>      writel(fep->phy_speed, fep->hwp + FEC_MII_SPEED);
> 
> The code following this is:
> 
>          writel(fep->phy_speed, fep->hwp + FEC_MII_SPEED);
> 
>          /* Clear any pending transaction complete indication */
>          writel(FEC_ENET_MII, fep->hwp + FEC_IEVENT);
> 
> 
> So this is forcing a clear of the event here. Is that not good enough?
> 
> For me on my ColdFire test target I always get a timeout if I wait for a
> FEC_IEVENT after the FEC_MII_SPEED write.
> 
> Regards
> Greg

Dave Karr's last patch can fix the issue, but it may introduce 30ms delay during boot.
Greg's patch is to add quirk flag to distinguish platform before clearing mmfr operation,
which also can fix the issue. 

Andy