linux-kernel - Re: [PATCH v2 3/4] usb: dwc3: qcom: Facilitate autosuspend during host mode

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Message-ID: <5pbdk3xo6jkj7gwxlgvzdz4nxehjm6izgejjvwafxitvn6lm5p@qhjfezk3dvdh>
Date: Tue, 10 Jun 2025 20:24:19 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Krishna Kurapati <krishna.kurapati@....qualcomm.com>
Cc: Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Bjorn Andersson <bjorn.andersson@....qualcomm.com>,
        linux-arm-msm@...r.kernel.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/4] usb: dwc3: qcom: Facilitate autosuspend during
 host mode

On Tue, Jun 10, 2025 at 10:10:33PM +0530, Krishna Kurapati wrote:
> 
> 
> On 6/10/2025 4:30 PM, Dmitry Baryshkov wrote:
> > On Tue, Jun 10, 2025 at 02:43:56PM +0530, Krishna Kurapati wrote:
> > > When in host mode, it is intended that the controller goes to suspend
> > > state to save power and wait for interrupts from connected peripheral
> > > to wake it up. This is particularly used in cases where a HID or Audio
> > > device is connected. In such scenarios, the usb controller can enter
> > > auto suspend and resume action after getting interrupts from the
> > > connected device.
> > > 
> > > Allow autosuspend for and xhci device and allow userspace to decide
> > > whether to enable this functionality.
> > > 
> > > a) Register to usb-core notifications in set_role vendor callback to
> > > identify when root hubs are being created. Configure them to
> > > use_autosuspend.
> > > 
> > > b) Identify usb core notifications where the HCD is being added and
> > > enable autosuspend for that particular xhci device.
> > > 
> > > Signed-off-by: Krishna Kurapati <krishna.kurapati@....qualcomm.com>
> > > ---
> > >   drivers/usb/dwc3/dwc3-qcom.c | 62 ++++++++++++++++++++++++++++++++----
> > >   1 file changed, 56 insertions(+), 6 deletions(-)
> > > 
> > > diff --git a/drivers/usb/dwc3/dwc3-qcom.c b/drivers/usb/dwc3/dwc3-qcom.c
> > > index d40b52e2ba01..17bbd5a06c08 100644
> > > --- a/drivers/usb/dwc3/dwc3-qcom.c
> > > +++ b/drivers/usb/dwc3/dwc3-qcom.c
> > > @@ -95,6 +95,8 @@ struct dwc3_qcom {
> > >   	 * internally by mutex lock.
> > >   	 */
> > >   	enum usb_role		current_role;
> > > +
> > > +	struct notifier_block	xhci_nb;
> > >   };
> > >   #define to_dwc3_qcom(d) container_of((d), struct dwc3_qcom, dwc)
> > > @@ -647,6 +649,39 @@ static int dwc3_qcom_setup_irq(struct dwc3_qcom *qcom, struct platform_device *p
> > >   	return 0;
> > >   }
> > > +static int dwc3_xhci_event_notifier(struct notifier_block *nb,
> > > +				    unsigned long event, void *ptr)
> > > +{
> > > +	struct dwc3_qcom  *qcom	= container_of(nb, struct dwc3_qcom, xhci_nb);
> > > +	struct dwc3	  *dwc	= &qcom->dwc;
> > > +	struct usb_bus	  *ubus	= ptr;
> > > +	struct usb_hcd	  *hcd;
> > > +
> > > +	if (!dwc->xhci)
> > > +		goto done;
> > > +
> > > +	hcd = platform_get_drvdata(dwc->xhci);
> > > +	if (!hcd)
> > > +		goto done;
> > > +
> > > +	if (event != USB_BUS_ADD)
> > > +		goto done;
> > > +
> > > +	if (strcmp(dev_name(ubus->sysdev), dev_name(dwc->sysdev)) != 0)
> > > +		goto done;
> > > +
> > > +	if (event == USB_BUS_ADD) {
> > > +		/*
> > > +		 * Identify instant of creation of primary hcd and
> > > +		 * mark xhci as autosuspend capable at this point.
> > > +		 */
> > > +		pm_runtime_use_autosuspend(&dwc->xhci->dev);
> > 
> > This feels like an overkill, using notifiers to set autosuspend flag.
> > Please extend platform data and/or other static code in order to set the
> > flag on the created xHCI devices.
> > 
> 
> Do you mean modifying pdev of xhci from dwc3/host.c ? Or adding the
> use_autosuspend call in xhci-plat.c ?

The latter one.

> 
> I thought adding this notifier would be a better way to identify when the
> xhci probe is in progress instead of touching pdev of xhci device from dwc3
> layer.
> 
> Regards,
> Krishna,

-- 
With best wishes
Dmitry