netdev - Re: [PATCH] net: ethernet: fec: Clear stale flag in IEVENT register before MII transfers

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Date:   Wed, 9 Dec 2020 17:51:48 +0100
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Andrew Lunn <andrew@...n.ch>, mci@...gutronix.de
Cc:     netdev@...r.kernel.org, Fugang Duan <fugang.duan@....com>,
        "David S. Miller" <davem@...emloft.net>, kernel@...gutronix.de
Subject: Re: [PATCH] net: ethernet: fec: Clear stale flag in IEVENT register
 before MII transfers

Hi Andrew,

On Wed, Dec 09, 2020 at 03:44:13PM +0100, Andrew Lunn wrote:
> On Wed, Dec 09, 2020 at 11:29:59AM +0100, Uwe Kleine-König wrote:
> Do you have
> 
> ommit 1e6114f51f9d4090390fcec2f5d67d8cc8dc4bfc
> Author: Greg Ungerer <gerg@...ux-m68k.org>
> Date:   Wed Oct 28 15:22:32 2020 +1000
> 
>     net: fec: fix MDIO probing for some FEC hardware blocks
>     
>     Some (apparently older) versions of the FEC hardware block do not like
>     the MMFR register being cleared to avoid generation of MII events at
>     initialization time. The action of clearing this register results in no
>     future MII events being generated at all on the problem block. This means
>     the probing of the MDIO bus will find no PHYs.
>     
>     Create a quirk that can be checked at the FECs MII init time so that
>     the right thing is done. The quirk is set as appropriate for the FEC
>     hardware blocks that are known to need this.
> 
> in your tree?

Unless I did something wrong I also saw the failure with v5.10-rc$latest
earlier today.

... some time later ...

Argh, I checked my git reflog and the newest release I tested was
5.9-rc8.

I wonder if my patch is a simpler and more straight forward fix for the
problem however, but that might also be because I don't understand the
comment touched by 1e6114f51f9d4090390fcec2f5d67d8cc8dc4bfc without
checking the reference manual (which I didn't).

@Marian: As it's you who has to work on this i.MX25 machine, can you
maybe test if using a kernel > 5.10-rc3 (or cherry-picking
1e6114f51f9d4090390fcec2f5d67d8cc8dc4bfc) fixes the problem for you?

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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