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

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Message-ID: <3xjjx3dwqgtycasjystk4mcqzunut4mq2uzhc67ihr5eq6gcpb@r7ccsplb3tjy>
Date: Fri, 12 Sep 2025 15:49:26 +0800
From: Xu Yang <xu.yang_2@....com>
To: ryan zhou <ryanzhou54@...il.com>
Cc: Thinh Nguyen <Thinh.Nguyen@...opsys.com>, 
	"stern@...land.harvard.edu" <stern@...land.harvard.edu>, "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>, 
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>, "rafael@...nel.org" <rafael@...nel.org>, 
	"royluo@...gle.com" <royluo@...gle.com>
Subject: Re: [PATCH v2] drvier: usb: dwc3: Fix runtime PM trying to activate
 child device xxx.dwc3 but parent is not active

On Thu, Sep 11, 2025 at 09:51:50PM +0800, ryan zhou wrote:
> Hi Xu，
> 
> Xu Yang <xu.yang_2@....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@...il.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.

Can you provide more detail about point 2? When is the USB device inserted?
Is the re-enter behavior caused by pm_runtime_resume()?

Thanks,
Xu Yang

> 
> > 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;