[PATCH v3] phy: qcom-qusb2: Fix NULL pointer dereference on early suspend

[Loic Poulain]

Hi Dmitry,

On Fri, Dec 12, 2025 at 8:30 PM Dmitry Baryshkov
<dmitry.baryshkov at oss.qualcomm.com> wrote:
>
> On Thu, Dec 11, 2025 at 04:35:36PM +0100, Loic Poulain wrote:
> > Enabling runtime PM before attaching the QPHY instance as driver data
> > can lead to a NULL pointer dereference in runtime PM callbacks that
> > expect valid driver data. There is a small window where the suspend
> > callback may run after PM runtime enabling and before runtime forbid.
> > This causes a sporadic crash during boot:
> >
> > ```
> > Unable to handle kernel NULL pointer dereference at virtual address 00000000000000a1
> > [...]
> > CPU: 0 UID: 0 PID: 11 Comm: kworker/0:1 Not tainted 6.16.7+ #116 PREEMPT
> > Workqueue: pm pm_runtime_work
> > pstate: 20000005 (nzCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> > pc : qusb2_phy_runtime_suspend+0x14/0x1e0 [phy_qcom_qusb2]
> > lr : pm_generic_runtime_suspend+0x2c/0x44
> > [...]
> > ```
> >
> > Attach the QPHY instance as driver data before enabling runtime PM to
> > prevent NULL pointer dereference in runtime PM callbacks.
> >
> > Reorder pm_runtime_enable() and pm_runtime_forbid() to prevent a
> > short window where an unnecessary runtime suspend can occur.
> >
> > Use the devres-managed version to ensure PM runtime is symmetrically
> > disabled during driver removal for proper cleanup.
> >
> > Fixes: 891a96f65ac3 ("phy: qcom-qusb2: Add support for runtime PM")
> > Signed-off-by: Loic Poulain <loic.poulain at oss.qualcomm.com>
> > Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov at oss.qualcomm.com>
> > ---
> >  v3: The phy-core expects parent's runtime-pm to be setup before creating
> >      the phy, so move back runtime-pm to its initial location and
> >      relocate dev_set_drvdata() instead.
> >
> >  v2: Move runtime-pm enabling after dev_set_drvdata
> >      use devm_pm_runtime_enable() to fix unbalanced enabling on removal
> >      reword commit message
> >
> >  drivers/phy/qualcomm/phy-qcom-qusb2.c | 14 ++++++--------
> >  1 file changed, 6 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/phy/qualcomm/phy-qcom-qusb2.c b/drivers/phy/qualcomm/phy-qcom-qusb2.c
> > index b5514a32ff8f..6386d834b0e4 100644
> > --- a/drivers/phy/qualcomm/phy-qcom-qusb2.c
> > +++ b/drivers/phy/qualcomm/phy-qcom-qusb2.c
> > @@ -1093,29 +1093,27 @@ static int qusb2_phy_probe(struct platform_device *pdev)
> >               or->hsdisc_trim.override = true;
> >       }
> >
> > -     pm_runtime_set_active(dev);
> > -     pm_runtime_enable(dev);
> > +     dev_set_drvdata(dev, qphy);
> > +
> >       /*
> > -      * Prevent runtime pm from being ON by default. Users can enable
> > -      * it using power/control in sysfs.
> > +      * Enable runtime PM support, but forbid it by default.
> > +      * Users can allow it again via the power/control attribute in sysfs.
> >        */
> > +     pm_runtime_set_active(dev);
> >       pm_runtime_forbid(dev);
>
> I think, this should be called after enabling runtime PM. Please correct
> me if I'm wrong.

enable/disable and forbid/allow appear to be orthogonal, the purpose
of inverting them here is to prevent an unnecessary suspend/resume
cycle from occurring between enable and forbid. Also, this sequence
has been tested and works correctly.

>
> > +     devm_pm_runtime_enable(dev);
>
> Missing error handling

I wasn’t certain whether we should abort on this non-fatal error,
since the driver can operate without PM-runtime enabled. However, if
this error occurs, it likely indicates a more significant underlying
memory issue.


>
> >
> >       generic_phy = devm_phy_create(dev, NULL, &qusb2_phy_gen_ops);
> >       if (IS_ERR(generic_phy)) {
> >               ret = PTR_ERR(generic_phy);
> >               dev_err(dev, "failed to create phy, %d\n", ret);
> > -             pm_runtime_disable(dev);
> >               return ret;
> >       }
> >       qphy->phy = generic_phy;
> >
> > -     dev_set_drvdata(dev, qphy);
> >       phy_set_drvdata(generic_phy, qphy);
> >
> >       phy_provider = devm_of_phy_provider_register(dev, of_phy_simple_xlate);
> > -     if (IS_ERR(phy_provider))
> > -             pm_runtime_disable(dev);
> >
> >       return PTR_ERR_OR_ZERO(phy_provider);
> >  }
> > --
> > 2.34.1
> >
>
> --
> With best wishes
> Dmitry