linux-kernel - Re: [PATCH] net: bcmgenet: Fix attaching to PYH failed on RPi 4B

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Date:   Mon, 21 Jun 2021 22:15:42 +0200
From:   Stefan Wahren <stefan.wahren@...e.com>
To:     Peter Robinson <pbrobinson@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>, Jian-Hong Pan <jhp@...lessos.org>,
        Doug Berger <opendmb@...il.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux@...lessos.org,
        bcm-kernel-feedback-list@...adcom.com,
        linux-rpi-kernel@...ts.infradead.org
Subject: Re: [PATCH] net: bcmgenet: Fix attaching to PYH failed on RPi 4B

Am 21.06.21 um 18:56 schrieb Peter Robinson:
> On Mon, Jun 21, 2021 at 5:39 PM Florian Fainelli <f.fainelli@...il.com> wrote:
>> On 6/21/21 6:09 AM, Andrew Lunn wrote:
>>> On Mon, Jun 21, 2021 at 06:33:11PM +0800, Jian-Hong Pan wrote:
>>>> The Broadcom UniMAC MDIO bus comes too late. So, GENET cannot find the
>>>> ethernet PHY on UniMAC MDIO bus. This leads GENET fail to attach the
>>>> PHY.
>>>>
>>>> bcmgenet fd580000.ethernet: GENET 5.0 EPHY: 0x0000
>>>> ...
>>>> could not attach to PHY
>>>> bcmgenet fd580000.ethernet eth0: failed to connect to PHY
>>>> uart-pl011 fe201000.serial: no DMA platform data
>>>> libphy: bcmgenet MII bus: probed
>>>> ...
>>>> unimac-mdio unimac-mdio.-19: Broadcom UniMAC MDIO bus
>>>>
>>>> This patch makes GENET try to connect the PHY up to 3 times. Also, waits
>>>> a while between each time for mdio-bcm-unimac module's loading and
>>>> probing.
>>> Don't loop. Return -EPROBE_DEFER. The driver core will then probed the
>>> driver again later, by which time, the MDIO bus driver should of
>>> probed.
>> This is unlikely to work because GENET register the mdio-bcm-unimac
>> platform device so we will likely run into a chicken and egg problem,
>> though surprisingly I have not seen this on STB platforms where GENET is
>> used, I will try building everything as a module like you do. Can you
>> see if the following helps:
> For reference we have mdio_bcm_unimac/genet both built as modules in
> Fedora and I've not seen this issue reported using vanilla upstream
> kernels if that's a useful reference point.

I was also unable to reproduce this issue, but it seems to be a known
issue [1], [2].

Jian-Hong opened an issue in my Github repo [3], but before the issue
was narrowed down, he decided to send this workaround.

Best regards

[1] -
https://github.com/raspberrypi/linux/issues/3108#issuecomment-723550749
[2] - https://archlinuxarm.org/forum/viewtopic.php?f=67&t=14806
[3] - https://github.com/lategoodbye/rpi-zero/issues/51

>
> Regards,
> Peter
>
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