linux-kernel - Re: [PATCH net v2] net: bcmgenet: Clear ID_MODE_DIS in EXT_RGMII_OOB

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Date:   Thu, 7 May 2020 12:03:48 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        Doug Berger <opendmb@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Stefan Wahren <wahrenst@....net>
Cc:     bcm-kernel-feedback-list@...adcom.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net v2] net: bcmgenet: Clear ID_MODE_DIS in
 EXT_RGMII_OOB_CTRL when not needed

Hi

On 07.05.2020 11:46, Marek Szyprowski wrote:
> On 25.02.2020 14:11, Nicolas Saenz Julienne wrote:
>> Outdated Raspberry Pi 4 firmware might configure the external PHY as
>> rgmii although the kernel currently sets it as rgmii-rxid. This makes
>> connections unreliable as ID_MODE_DIS is left enabled. To avoid this,
>> explicitly clear that bit whenever we don't need it.
>>
>> Fixes: da38802211cc ("net: bcmgenet: Add RGMII_RXID support")
>> Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
>
> I've finally bisected the network issue I have on my RPi4 used for 
> testing mainline builds. The bisect pointed to this patch. Once it got 
> applied in v5.7-rc1, the networking is broken on my RPi4 in ARM32bit 
> mode and kernel compiled from bcm2835_defconfig. I'm using u-boot to 
> tftp zImage/dtb/initrd there. After reverting this patch network is 
> working fine again. The strange thing is that networking works fine if 
> kernel is compiled from multi_v7_defconfig but I don't see any obvious 
> difference there.
>
> I'm not sure if u-boot is responsible for this break, but kernel 
> definitely should be able to properly reset the hardware to the valid 
> state.
>
> I can provide more information, just let me know what is needed. Here 
> is the log, I hope it helps:
>
> [   11.881784] bcmgenet fd580000.ethernet eth0: Link is Up - 
> 1Gbps/Full - flow control off
> [   11.889935] IPv6: ADDRCONF(NETDEV_CHANGE): eth0: link becomes ready
>
> root@...get:~# ping host
> PING host (192.168.100.1) 56(84) bytes of data.
> From 192.168.100.53 icmp_seq=1 Destination Host Unreachable
> ...

Okay, I've played a bit more with this and found that enabling 
CONFIG_BROADCOM_PHY fixes this network issue. I wonder if Genet driver 
should simply select CONFIG_BROADCOM_PHY the same way as it selects 
CONFIG_BCM7XXX_PHY.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland