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Subject: Re: [PATCH] net: fec: fix probing of fec1 when fec0 is not probed yet
To:     Wei Fang <wei.fang@nxp.com>, Andrew Lunn <andrew@lunn.ch>,
        Heiko Schocher <heiko.schocher@gmail.com>
Cc:     "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        Clark Wang <xiaoning.wang@nxp.com>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        dl-linux-imx <linux-imx@nxp.com>,
        Paolo Abeni <pabeni@redhat.com>,
        Shenwei Wang <shenwei.wang@nxp.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Alexander Sverdlin <alexander.sverdlin@siemens.com>
References: <20231123132744.62519-1-hs@denx.de>
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From:   Heiko Schocher <hs@denx.de>
Message-ID: <227dc52c-c555-34e4-d534-1a749af15425@denx.de>
Date:   Fri, 24 Nov 2023 06:19:29 +0100
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Hello Wei,

On 24.11.23 03:33, Wei Fang wrote:
>> -----Original Message-----
>> From: Andrew Lunn <andrew@lunn.ch>
>> Sent: 2023??11??24?? 4:09
>> To: Heiko Schocher <heiko.schocher@gmail.com>
>> Cc: netdev@vger.kernel.org; Heiko Schocher <hs@denx.de>; Clark Wang
>> <xiaoning.wang@nxp.com>; David S. Miller <davem@davemloft.net>; Eric
>> Dumazet <edumazet@google.com>; Jakub Kicinski <kuba@kernel.org>;
>> dl-linux-imx <linux-imx@nxp.com>; Paolo Abeni <pabeni@redhat.com>;
>> Shenwei Wang <shenwei.wang@nxp.com>; Wei Fang <wei.fang@nxp.com>;
>> linux-kernel@vger.kernel.org
>> Subject: Re: [PATCH] net: fec: fix probing of fec1 when fec0 is not probed yet
>>
>> On Thu, Nov 23, 2023 at 02:27:43PM +0100, Heiko Schocher wrote:
>>> it is possible that fec1 is probed before fec0. On SoCs with
>>> FEC_QUIRK_SINGLE_MDIO set (which means fec1 uses mii from fec0) init
>>> of mii fails for fec1 when fec0 is not yet probed, as fec0 setups mii
>>> bus. In this case fec_enet_mii_init for fec1 returns with -ENODEV, and
>>> so fec1 never comes up.
>>>
>>> Return here with -EPROBE_DEFER so interface gets later probed again.
>>>
>>> Found this on imx8qxp based board, using 2 ethernet interfaces, and
>>> from time to time, fec1 interface came not up.
>>>
>>> Signed-off-by: Heiko Schocher <hs@denx.de>
>>> ---
>>>
>>>  drivers/net/ethernet/freescale/fec_main.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/net/ethernet/freescale/fec_main.c
>>> b/drivers/net/ethernet/freescale/fec_main.c
>>> index c3b7694a7485..d956f95e7a65 100644
>>> --- a/drivers/net/ethernet/freescale/fec_main.c
>>> +++ b/drivers/net/ethernet/freescale/fec_main.c
>>> @@ -2445,7 +2445,7 @@ static int fec_enet_mii_init(struct
>> platform_device *pdev)
>>>  			mii_cnt++;
>>>  			return 0;
>>>  		}
>>> -		return -ENOENT;
>>> +		return -EPROBE_DEFER;
>>
>> I think this has been tried before.
>>
> Yes, there was indeed a similar patch [1] before. but this issue seems to only exist
> in downstream tree, because there is a local patch which is not in the upstream.
> 
>         /* board only enable one mii bus in default */
>         if (!of_get_property(np, "fsl,mii-exclusive", NULL))
>                 fep->quirks |= FEC_QUIRK_SINGLE_MDIO;

Yes, sorry for overseeing this ... but there are SoCs in upstream which
set FEC_QUIRK_SINGLE_MDIO and so mii bus from for example fec0 is used on
other fecX devices, correct?

And for them probing currently fail, when probed before fec0.

> I will think about how to solve this issue in downstream if I'm free later.
> 
> [1] https://lore.kernel.org/lkml/20230208101821.871269-1-alexander.sverdlin@siemens.com/T/#r6313852054bf12baabe21418584fbb6d58343197

Hmm.. simply deferring the probe to later point solves the problem here.

I added Alexander may he can comment...

bye,
Heiko
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