Re: [PATCH] net: fec: defer probe if PHY on external MDIO bus is not available

From: Matthias Schiffer
Date: Fri Oct 22 2021 - 03:58:01 EST


On Thu, 2021-10-21 at 14:50 +0200, Andrew Lunn wrote:
> > 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


Hmm, lots of network drivers? I tried to find an example, but all
drivers that generate -EPROBE_DEFER for missing PHYs at all don't have
an internal MDIO bus and thus avoid the circular dependency.

Matthias