linux-kernel - Re: [PATCH] net: fec: fix probing of fec1 when fec0 is not probed yet

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Message-ID: <307682f4-b691-7198-ba96-454b973bd555@denx.de>
Date:   Fri, 24 Nov 2023 06:09:14 +0100
From:   Heiko Schocher <hs@...x.de>
To:     Andrew Lunn <andrew@...n.ch>,
        Heiko Schocher <heiko.schocher@...il.com>
Cc:     netdev@...r.kernel.org, Clark Wang <xiaoning.wang@....com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        NXP Linux Team <linux-imx@....com>,
        Paolo Abeni <pabeni@...hat.com>,
        Shenwei Wang <shenwei.wang@....com>,
        Wei Fang <wei.fang@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: fec: fix probing of fec1 when fec0 is not probed yet

Hello Andrew,

On 23.11.23 21:09, Andrew Lunn wrote:
> 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@...x.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.

Oh, wasn;t aware of it...

> Are there any issues with the mii_cnt++; I thought the previous
> attempt as this had problems with the wrong mdio bus being assigned to
> fep->mii_bus ? But i could be remembering wrongly.

The problem with returning -ENOENT is, that the probe never called
again ... with returning -EPROBE_DEFER, the device gets probed
later again.

bye,
Heiko
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