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

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Message-ID: <AM8PR04MB73153FA5CF4C0B88CE65EF87FF1C0@AM8PR04MB7315.eurprd04.prod.outlook.com>
Date:   Wed, 21 Oct 2020 02:19:19 +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: Wednesday, October 21, 2020 9:52 AM
> Hi Andrew,
> 
> Thanks for the quick response.
> 
> 
> On 20/10/20 12:40 pm, Andrew Lunn wrote:
> > On Tue, Oct 20, 2020 at 12:14:04PM +1000, Greg Ungerer wrote:
> >> Hi Andrew,
> >>
> >> Commit f166f890c8f0 ("[PATCH] net: ethernet: fec: Replace interrupt
> >> driven MDIO with polled IO") breaks the FEC driver on at least one of
> >> the ColdFire platforms (the 5208). Maybe others, that is all I have
> >> tested on so far.
> >>
> >> Specifically the driver no longer finds any PHY devices when it
> >> probes the MDIO bus at kernel start time.
> >>
> >> I have pinned the problem down to this one specific change in this commit:
> >>
> >>> @@ -2143,8 +2142,21 @@ static int fec_enet_mii_init(struct
> platform_device *pdev)
> >>>     if (suppress_preamble)
> >>>             fep->phy_speed |= BIT(7);
> >>> +   /* 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);
> >>
> >> At least by removing this I get the old behavior back and everything
> >> works as it did before.
> >>
> >> With that write of the FEC_MII_DATA register in place it seems that
> >> subsequent MDIO operations return immediately (that is FEC_IEVENT is
> >> set) - even though it is obvious the MDIO transaction has not completed yet.
> >>
> >> Any ideas?
> >
> > Hi Greg
> >
> > This has come up before, but the discussion fizzled out without a
> > final patch fixing the issue. NXP suggested this
> >
> > writel(0, fep->hwp + FEC_MII_DATA);
> >
> > Without it, some other FEC variants break because they do generate an
> > interrupt at the wrong time causing all following MDIO transactions to
> > fail.
> >
> > At the moment, we don't seem to have a clear understanding of the
> > different FEC versions, and how their MDIO implementations vary.
> 
> Based on Andy and Chris' comments is something like the attached patch what
> we need?

Greg, imx28 platform also requires the flag.
> 
> Regards
> Greg
>