RE: [PATCH] net: fec: fix probing of fec1 when fec0 is not probed yet

[Wei Fang]

> -----Original Message-----
> From: Andrew Lunn <andrew@xxxxxxx>
> Sent: 2023年11月24日 4:09
> To: Heiko Schocher <heiko.schocher@xxxxxxxxx>
> Cc: netdev@xxxxxxxxxxxxxxx; Heiko Schocher <hs@xxxxxxx>; Clark Wang
> <xiaoning.wang@xxxxxxx>; David S. Miller <davem@xxxxxxxxxxxxx>; Eric
> Dumazet <edumazet@xxxxxxxxxx>; Jakub Kicinski <kuba@xxxxxxxxxx>;
> dl-linux-imx <linux-imx@xxxxxxx>; Paolo Abeni <pabeni@xxxxxxxxxx>;
> Shenwei Wang <shenwei.wang@xxxxxxx>; Wei Fang <wei.fang@xxxxxxx>;
> linux-kernel@xxxxxxxxxxxxxxx
> 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@xxxxxxx>
> > ---
> >
> >  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;

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@xxxxxxxxxxx/T/#r6313852054bf12baabe21418584fbb6d58343197

> 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.
>