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

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Date:   Tue, 20 Oct 2020 12:14:04 +1000
From:   Greg Ungerer <gerg@...ux-m68k.org>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Chris Heally <cphealy@...il.com>, netdev@...r.kernel.org,
        Fugang Duan <fugang.duan@....com>
Subject: Re: [PATCH] net: ethernet: fec: Replace interrupt driven MDIO with
 polled IO

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?

Regards
Greg