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

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Message-ID: <5d692b81-6f58-4e86-9cb0-ede69a09d799@rowland.harvard.edu>
Date: Wed, 27 Aug 2025 10:52:17 -0400
From: Alan Stern <stern@...land.harvard.edu>
To: ryan zhou <ryanzhou54@...il.com>,
	"Rafael J. Wysocki" <rafael@...nel.org>
Cc: Roy Luo <royluo@...gle.com>, Thinh.Nguyen@...opsys.com,
	gregkh@...uxfoundation.org, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH] drvier: usb: dwc3: Fix runtime PM trying to activate
 child device xxx.dwc3 but parent is not active

Ryan:

You should present your questions to the maintainer of the kernel's 
Power Management subsystem, Rafael Wysocki (added to the To: list for 
this email).

Alan Stern

On Wed, Aug 27, 2025 at 10:09:10PM +0800, ryan zhou wrote:
> Hi Roy,
> Thank you for reviewing my patch.
> >
> > Wouldn't the parent glue dev already resume before resuming the child dwc3?
> >
> No, in the following case, the parent device will not be reviewed
> before resuming the child device.
> Taking the 'imx8mp-dwc3' driver as an example.
> Step 1.usb disconnect trigger: the child device dwc3 enter runtime
> suspend state firstly, followed by
> the parent device imx8mp-dwc3 enters runtime suspend
> flow:dwc3_runtime_suspend->dwc3_imx8mp_runtime_suspend
> Step2.system deep trigger:consistent with the runtime suspend flow,
> child enters pm suspend and followed
> by parent
> flow: dwc3_pm_suspend->dwc3_imx8mp_pm_suspend
> Step3: After dwc3_pm_suspend, and before dwc3_imx8mp_pm_suspend, a
> task terminated the system suspend process
> . The system will resume from the checkpoint, and resume devices in
> the suspended state in the reverse
> of pm suspend, but excluding the parent device imx8mp-dwc3 since it
> did not execute the suspend process.
> 
> >
> >Why would 'runtime PM trying to activate child device xxx.dwc3 but parent is not active' happen in the first place?
> >
> Following the above analysis, dwc3_resume calls
> pm_runtime_set_active(dev), it checks the
> parent.power->runtime_status is not RPM_ACTIVE and outputs the error log.
> 
> >
> >What is the glue driver that's being used here? Knowing what's being done in the glue driver pm callbacks
> >would help in understanding the issue.
> >
> Refer to the driver 'dwc3-imx8mp.c' please, maybe you could help me
> find a better solution.
> 
> 
> Thanks,
> ryan
> 
> Roy Luo <royluo@...gle.com> 于2025年8月27日周三 02:38写道：
> >
> > On Tue, Aug 26, 2025 at 8:12 AM Ryan Zhou <ryanzhou54@...il.com> wrote:
> > >
> > > Issue description:
> > > The parent device dwc3_glue has runtime PM enabled and is in the
> > > runtime suspended state. The system enters the deep sleep process
> > > but is interrupted by another task. When resuming dwc3,
> > > console outputs the log 'runtime PM trying to activate child device
> > > xxx.dwc3 but parent is not active'.
> > >
> >
> > Wouldn't the parent glue dev already resume before resuming the child dwc3?
> > Why would 'runtime PM trying to activate child device xxx.dwc3 but parent is
> > not active' happen in the first place?
> > What is the glue driver that's being used here? Knowing what's being done in
> > the glue driver pm callbacks would help in understanding the issue.
> >
> > Regards,
> > Roy
>