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: <20250830011437.g4m7jqvymfg7tm6x@synopsys.com>
Date: Sat, 30 Aug 2025 01:14:37 +0000
From: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To: Alan Stern <stern@...land.harvard.edu>
CC: Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        ryan zhou <ryanzhou54@...il.com>, Roy Luo <royluo@...gle.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pm@...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

On Fri, Aug 29, 2025, Alan Stern wrote:
> On Fri, Aug 29, 2025 at 08:13:07PM +0000, Thinh Nguyen wrote:
> > ..shouldn't the PM core know that A was runtime suspended to not skip
> > ->resume? (sorry I'm not an expert in the PM core, genuine question
> > here).
> 
> This doesn't answer your question directly, but I would like to add some 
> background.
> 
> There are subsystems/drivers that do want to resume their devices during 
> system resume, even if the devices were in runtime suspend originally.  
> At a minimum, the PM core doesn't want to take this choice away from 
> them.
> 
> In fact, the USB subsystem was designed to run that way back when 
> support for runtime PM was first added, and it hasn't been changed since 
> -- although maybe it should be.  There are explicit mechanisms for 
> telling the PM core that a device should be skipped during system 
> resume; we could use them.
> 
> Regardless, I don't recall any discussions of the particular situation 
> in this thread ever taking place.
> 

Thank you for the background Alan.

I'm glad that we're having this discussion now. I'll continue to monitor
this thread. Do let me know how we should handle this case.

Thanks,
Thinh