linux-kernel - Re: (EXT) Re: [PATCH] net: fec: defer probe if PHY on external MDIO bus is not available

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Message-ID: <YXFh/nLTqvCsLAXj@lunn.ch>
Date:   Thu, 21 Oct 2021 14:50:06 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Matthias Schiffer <matthias.schiffer@...tq-group.com>
Cc:     Joakim Zhang <qiangqing.zhang@....com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: (EXT) Re: [PATCH] net: fec: defer probe if PHY on external MDIO
 bus is not available

> I would love to do this, but driver-api/driver-model/driver.rst
> contains the following warning:
> 
>       -EPROBE_DEFER must not be returned if probe() has already created
>       child devices, even if those child devices are removed again
>       in a cleanup path. If -EPROBE_DEFER is returned after a child
>       device has been registered, it may result in an infinite loop of
>       .probe() calls to the same driver.
> 
> My understanding of this is that there is simply no way to return
> -EPROBE_DEFER after fec_enet_mii_init(pdev).

It might say that, but lots of network drivers actually do this. I've
not seen an endless loop.

    Andrew