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

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Date:   Tue, 27 Oct 2020 01:33:14 +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: Tuesday, October 27, 2020 8:18 AM
> Hi Andy,
> 
> On 22/10/20 7:04 pm, Andy Duan wrote:
> > 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.
> 
> Do you mean that we can use either fix - and that is ok for all hardware types?
> 
> Regards
> Greg

Yes, I think so.

Thanks,
Andy