Re: [PATCH v3 5/5] phy: qcom: snps-femto-v2: Fix possible NULL-deref on early runtime suspend

[Johan Hovold <johan@kernel.org>]

On Fri, Feb 13, 2026 at 04:04:43PM +0100, Loic Poulain wrote:
> On Fri, Feb 13, 2026 at 11:45 AM Johan Hovold <johan@kernel.org> wrote:

> > But I'm literally asking for *what* would trigger the suspend in that
> > initial window between enable() and forbid() cause I don't see it.
> 
> To be honest, I had not initially looked into the exact cause of the
> suspend trigger until now, but here is what is happening.
> 
> The PHY is a supplier of the USB device. A USB device cannot be probed
> until all its suppliers are ready. As long as the PHY is not ready, the
> device core keeps retrying the probe, which fails with -EPROBE_DEFER.
> 
> At some point the PHY probe finally runs, but the device core may still be
> attempting to probe the USB device concurrently.
> 
> Inside __driver_probe_device(), we have:
> 
>     ret = really_probe(dev, drv);
>     pm_request_idle(dev);
> 
>     if (dev->parent)
>         pm_runtime_put(dev->parent);
> 
>     pm_runtime_put_suppliers(dev);
>     return ret;
> 
> This means that whenever a USB probe attempt completes, whether with an
> error or not, its suppliers are released via pm_runtime_put_suppliers().
> Releasing suppliers may in turn trigger a runtime suspend.
> 
> In our case, since the PHY is a supplier of the USB device, the USB core
> keeps 'looping' in __driver_probe_device() returning -EPROBE_DEFER until
> the PHY becomes ready. As a result, pm_runtime_put_suppliers() may run
> concurrently with the PHY's probe function. If this happens after
> runtime PM has been enabled for the PHY, but before the driver has
> forbidden suspend or taken a PM reference, the PHY may end up being
> runtime-suspended 'unexpectedly'.

Thanks for tracking that down. That's an unexpected side effect of
fw_devlink adding runtime pm enabled links (which is the default
behaviour since late 2023).

Johan

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