linux-kernel - Re: [PATCH 5/5] usb: dwc3: qcom: Allow runtime PM

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Date:   Tue, 28 Mar 2023 15:35:29 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc:     andersson@...nel.org, Thinh.Nguyen@...opsys.com,
        gregkh@...uxfoundation.org, mathias.nyman@...el.com,
        konrad.dybcio@...aro.org, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, linux-arm-msm@...r.kernel.org,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH 5/5] usb: dwc3: qcom: Allow runtime PM

On Tue, Mar 28, 2023 at 06:27:05PM +0530, Manivannan Sadhasivam wrote:
> On Tue, Mar 28, 2023 at 02:18:16PM +0200, Johan Hovold wrote:

> > > > > @@ -948,6 +948,8 @@ static int dwc3_qcom_remove(struct platform_device *pdev)
> > > > >  	struct device *dev = &pdev->dev;
> > > > >  	int i;
> > > > >  
> > > > > +	pm_runtime_get_sync(dev);
> > > > 
> > > > This call needs to be balanced. But this is a fix for a bug in the
> > > > current implementation that should go in a separate patch.
> > > 
> > > Ok. For balancing I could add pm_runtime_put_noidle() before pm_runtime_disable.
> > 
> > You should do it after disabling runtime pm.
> 
> May I know why?

The usage counter should be balanced after disabling runtime PM so that
there is no window where you could get a racing suspend request.

> > > > > +
> > > > >  	device_remove_software_node(&qcom->dwc3->dev);
> > > > >  	of_platform_depopulate(dev);
> > > > >  
> > > > > @@ -960,7 +962,6 @@ static int dwc3_qcom_remove(struct platform_device *pdev)
> > > > >  	dwc3_qcom_interconnect_exit(qcom);
> > > > >  	reset_control_assert(qcom->resets);
> > > > >  
> > > > > -	pm_runtime_allow(dev);
> > > > >  	pm_runtime_disable(dev);
> > > > >  
> > > > >  	return 0;

Johan