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Date:   Sat, 30 Apr 2022 08:41:30 +0530
From:   Pavan Kondeti <quic_pkondeti@quicinc.com>
To:     Matthias Kaehlcke <mka@chromium.org>
CC:     Pavan Kondeti <quic_pkondeti@quicinc.com>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Sandeep Maheswaram <quic_c_sanm@quicinc.com>,
        "Rob Herring" <robh+dt@kernel.org>, Andy Gross <agross@kernel.org>,
        "Bjorn Andersson" <bjorn.andersson@linaro.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Felipe Balbi <balbi@kernel.org>,
        Stephen Boyd <swboyd@chromium.org>,
        Doug Anderson <dianders@chromium.org>,
        Mathias Nyman <mathias.nyman@intel.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Len Brown <len.brown@intel.com>, "Pavel Machek" <pavel@ucw.cz>,
        Linux PM <linux-pm@vger.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@vger.kernel.org>,
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        <quic_ppratap@quicinc.com>, <quic_kriskura@quicinc.com>,
        <quic_vpulyala@quicinc.com>
Subject: Re: [PATCH v14 2/7] PM / wakeup: Add device_children_wakeup_capable()
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Hi Matthias,

On Fri, Apr 29, 2022 at 12:19:22PM -0700, Matthias Kaehlcke wrote:
> Hi Pavan,
> 
> On Fri, Apr 29, 2022 at 06:29:56PM +0530, Pavan Kondeti wrote:
> > Hi Matthias,
> > 
> > On Mon, Apr 25, 2022 at 06:33:03PM +0530, Pavan Kondeti wrote:
> > > Hi Matthias,
> > > 
> > > On Fri, Apr 22, 2022 at 11:44:36AM -0700, Matthias Kaehlcke wrote:
> > > > On Fri, Apr 22, 2022 at 01:57:17PM +0200, Rafael J. Wysocki wrote:
> > > > > On Tue, Apr 19, 2022 at 9:11 PM Sandeep Maheswaram
> > > > > <quic_c_sanm@quicinc.com> wrote:
> > > > > >
> > > > > > From: Matthias Kaehlcke <mka@chromium.org>
> > > > > >
> > > > > > Add device_children_wakeup_capable() which checks whether the device itself
> > > > > > or one if its descendants is wakeup capable.
> > > > > 
> > > > > device_wakeup_path() exists for a very similar purpose.
> > > > > 
> > > > > Is it not usable for whatever you need the new function introduced here?
> > > > 
> > > > I wasn't aware of it's function, there are no doc comments and the
> > > > name isn't really self explanatory.
> > > > 
> > > > In a quick test device_wakeup_path() returned inconsistent values for the
> > > > root hub, sometimes true, others false when a wakeup capable USB device was
> > > > connected.
> > > 
> > > We will also test the same to double confirm the behavior of
> > > device_wakeup_path(). I am assuming that you checked device_wakeup_path()
> > > only during system suspend path.
> > > 
> > > Here is what I understood by looking at __device_suspend(). Please share
> > > your thoughts on this.
> > > 
> > > power.wakeup_path is set to true for the parent *after* a wakeup capable
> > > device is suspended. This means when the root hub(s) is suspended, it is
> > > propagated to xhci-plat and when xhci-plat is suspended, it is propagated
> > > to dwc3. bottom up propgation during system suspend.
> > > 
> > > I believe we can directly check something like this in the dwc3 driver
> > > instead of having another wrapper like device_children_wakeup_capable().
> > > 
> > > diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
> > > index 1170b80..a783257 100644
> > > --- a/drivers/usb/dwc3/core.c
> > > +++ b/drivers/usb/dwc3/core.c
> > > @@ -1878,8 +1878,14 @@ static int dwc3_suspend_common(struct dwc3 *dwc, pm_message_t msg)
> > >  		break;
> > >  	case DWC3_GCTL_PRTCAP_HOST:
> > >  		if (!PMSG_IS_AUTO(msg)) {
> > > +			/*
> > > +			 * Don't kill the host when dwc3 is wakeup capable and
> > > +			 * its children needs wakeup.
> > > +			 */
> > > +			if (device_may_wakeup(dwc->dev) && device_wakeup_path(dwc->dev))
> > > +				handle_it();
> > > +		} else {
> > >  			dwc3_core_exit(dwc);
> > > -			break;
> > >  		}
> > >  
> > >  		/* Let controller to suspend HSPHY before PHY driver suspends */
> > > 
> > 
> > device_wakeup_path(dwc->dev) is returning true all the time irrespective of
> > the wakeup capability (and enabled status) of the connected USB devices. That
> > is because xhci-plat device is configured to wakeup all the time. Since the
> > child is wakeup capable, its parent i.e dwc3 has device_wakeup_path() set.
> > device_children_wakeup_capable() will also suffer the problem. However,
> > 
> > device_children_wakeup_capable(&hcd->self.root_hub->dev) is what Sandeep's
> > patch is using. That is not correct. we have two root hubs (HS and SS) associated
> > with a USB3 controller and calling it on one root hub is incorrect. 
> > device_children_wakeup_capable() must be called on xhci-plat so that it covers
> > both HS and SS root hubs
> 
> Thanks for pointing that out!
> 
> > I am thinking of dynamically enabling/disabling xhci-plat wakeup capability so
> > that the wakeup path is correctly propagated to dwc3. something like below.
> > Does it make sense to you?
> > 
> > diff --git a/drivers/usb/host/xhci-plat.c b/drivers/usb/host/xhci-plat.c
> > index 649ffd8..be0c55b 100644
> > --- a/drivers/usb/host/xhci-plat.c
> > +++ b/drivers/usb/host/xhci-plat.c
> > @@ -412,6 +412,9 @@ static int __maybe_unused xhci_plat_suspend(struct device *dev)
> >  	struct xhci_hcd	*xhci = hcd_to_xhci(hcd);
> >  	int ret;
> >  
> > +	if (!device_wakeup_path(dev))
> > +		device_wakeup_disable(dev);
> > +
> >  	if (pm_runtime_suspended(dev))
> >  		pm_runtime_resume(dev);
> >  
> > @@ -443,6 +446,8 @@ static int __maybe_unused xhci_plat_resume(struct device *dev)
> >  	pm_runtime_set_active(dev);
> >  	pm_runtime_enable(dev);
> >  
> > +	device_wakeup_enable(dev);
> 
> I think this also needs to be done conditionally, otherwise it would
> create a new wake source on every resume when wakeup is already
> enabled.
> 
Right, this needs to be done conditionally. However, there is a silent
warning inside device_wakeup_enable() if it is called during system
transition. Not sure if we really need to worry about that or not.

Thanks,
Pavan