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

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Date:   Thu, 22 Oct 2020 02:39:45 +0000
From:   Andy Duan <fugang.duan@....com>
To:     Greg Ungerer <gerg@...ux-m68k.org>, Andrew Lunn <andrew@...n.ch>
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.

It is what I raised in previous mail about 30ms latency for boot. 
> 
> Regards
> Greg