linux-kernel - Re: [PATCH v14 2/7] PM / wakeup: Add device_children_wakeup

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Date:   Mon, 25 Apr 2022 18:33:03 +0530
From:   Pavan Kondeti <quic_pkondeti@...cinc.com>
To:     Matthias Kaehlcke <mka@...omium.org>
CC:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Sandeep Maheswaram <quic_c_sanm@...cinc.com>,
        Rob Herring <robh+dt@...nel.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        Felipe Balbi <balbi@...nel.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Doug Anderson <dianders@...omium.org>,
        Mathias Nyman <mathias.nyman@...el.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Len Brown <len.brown@...el.com>, "Pavel Machek" <pavel@....cz>,
        Linux PM <linux-pm@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        "open list:ULTRA-WIDEBAND (UWB) SUBSYSTEM:" 
        <linux-usb@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        <quic_pkondeti@...cinc.com>, <quic_ppratap@...cinc.com>,
        <quic_kriskura@...cinc.com>, <quic_vpulyala@...cinc.com>
Subject: Re: [PATCH v14 2/7] PM / wakeup: Add device_children_wakeup_capable()

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@...cinc.com> wrote:
> > >
> > > From: Matthias Kaehlcke <mka@...omium.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 */

Thanks,
Pavan