Re: [PATCH v14 2/7] PM / wakeup: Add device_children_wakeup_capable()

[Pavan Kondeti]

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@xxxxxxxxxxx> wrote:
> > > >
> > > > From: Matthias Kaehlcke <mka@xxxxxxxxxxxx>
> > > >
> > > > 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

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);
+
 	return 0;
 }
 
Thanks,
Pavan