Re: [PATCH v2] drvier: usb: dwc3: Fix runtime PM trying to activate child device xxx.dwc3 but parent is not active

ryan zhou
2025-09-11T13:52:03Z

Hi Xu，

Xu Yang <xu.yang_2@nxp.com> 于2025年9月11日周四 18:58写道：
>
> Hi Ryan,
>
> On Thu, Sep 11, 2025 at 01:32:47AM +0000, Thinh Nguyen wrote:
> > On Wed, Sep 10, 2025, Ryan Zhou wrote:
> > > Issue description:During the wake-up sequence, if the system invokes
> > > dwc3->resume and detects that the parent device of dwc3 is in a
> > > runtime suspend state, the system will generate an error: runtime PM
> > > trying to activate child device xxx.dwc3 but parent is not active.
> > >
> > > Solution:At the dwc3->resume entry point, if the dwc3 controller
> > > is detected in a suspended state, the function shall return
> > > immediately without executing any further operations.
> > >
> > > Signed-off-by: Ryan Zhou <ryanzhou54@gmail.com>
> > > ---
> > > drivers/usb/dwc3/core.c | 3 +++
> > > 1 file changed, 3 insertions(+)
> > >
> > > diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
> > > index 370fc524a468..06a6f8a67129 100644
> > > --- a/drivers/usb/dwc3/core.c
> > > +++ b/drivers/usb/dwc3/core.c
> > > @@ -2687,6 +2687,9 @@ int dwc3_pm_resume(struct dwc3 *dwc)
> > > struct device *dev = dwc->dev;
> > > int ret = 0;
> > >
> > > + if (pm_runtime_suspended(dev))
> > > + return ret;
> > > +
> >
> > Is this a documented behavior where the device should remain runtime
> > suspend on system resume? I feel that that this should be configurable
> > by the user or defined the PM core. I don't think we should change
> > default behavior here just to workaround the issue that we're facing.
> >
> > What if the user wants to keep the old behavior and resume up the device
> > on system resume?
>
> What about resume the device firstly if it's already runtime suspended when
> call dwc3_pm_suspend(). Therefor, the old behavior can be kept and the issue
> can be avoided.

Originally, I also believed that forcing the device to remain active
before PM suspend
was necessary. However, this approach has two drawbacks:
1. It prolongs the system's sleep transition time.
2. Worse, if a USB insertion wakes the system during enumeration,
the system may
re-enter sleep before the USB device is fully recognized.

> diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
> index 370fc524a468..1b8dbb260017 100644
> --- a/drivers/usb/dwc3/core.c
> +++ b/drivers/usb/dwc3/core.c
> @@ -2672,6 +2672,9 @@ int dwc3_pm_suspend(struct dwc3 *dwc)
> struct device *dev = dwc->dev;
> int ret;
>
> + if (pm_runtime_suspended(dev))
> + pm_runtime_resume(dev);
> +
> ret = dwc3_suspend_common(dwc, PMSG_SUSPEND);
> if (ret)
> return ret;