linux-kernel - Re: [PATCH] usb: dwc3: keep PHYs disabled during suspend

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Message-ID: <Ywd1VBjbQTUeD+vD@hovoldconsulting.com>
Date:   Thu, 25 Aug 2022 15:12:52 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Matthias Kaehlcke <mka@...omium.org>
Cc:     Johan Hovold <johan+linaro@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Felipe Balbi <balbi@...nel.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Krishna Kurapati <quic_kriskura@...cinc.com>,
        Pavankumar Kondeti <quic_pkondeti@...cinc.com>,
        linux-arm-msm@...r.kernel.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: dwc3: keep PHYs disabled during suspend

On Wed, Aug 24, 2022 at 09:41:49AM -0700, Matthias Kaehlcke wrote:
> On Wed, Aug 24, 2022 at 10:27:44AM +0200, Johan Hovold wrote:
> > On Tue, Aug 23, 2022 at 11:33:18AM -0700, Matthias Kaehlcke wrote:
> > > Hi Johan,
> > > 
> > > On Tue, Aug 23, 2022 at 02:40:47PM +0200, Johan Hovold wrote:
> > > > Commit 649f5c842ba3 ("usb: dwc3: core: Host wake up support from system
> > > > suspend") started leaving the PHYs enabled during suspend for
> > > > wakeup-capable controllers even though it turns out this had nothing to
> > > > do with wakeup.
> > > > 
> > > > Rather, the wakeup capability flag was (ab-)used as a proxy to configure
> > > > the suspend behaviour in an attempt to reduce power leakage on some
> > > > platforms.
> > > > 
> > > > Stop abusing the wakeup configuration and restore the 5.19 behaviour of
> > > > keeping the PHYs powered off during suspend. If needed, a dedicated
> > > > mechanism for configuring the PHY power state during suspend can be
> > > > added later.
> > > > 
> > > > Fixes: 649f5c842ba3 ("usb: dwc3: core: Host wake up support from system suspend")
> > > > Link: https://lore.kernel.org/r/Yuv7AM/5jtO/pgcm@google.com
> > > > Signed-off-by: Johan Hovold <johan+linaro@...nel.org>
> > > > ---

> > > > diff --git a/drivers/usb/dwc3/dwc3-qcom.c b/drivers/usb/dwc3/dwc3-qcom.c
> > > > index 9a94b1ab8f7a..9995395baa12 100644
> > > > --- a/drivers/usb/dwc3/dwc3-qcom.c
> > > > +++ b/drivers/usb/dwc3/dwc3-qcom.c
> > > > @@ -904,7 +904,6 @@ static int dwc3_qcom_probe(struct platform_device *pdev)
> > > >  
> > > >  	wakeup_source = of_property_read_bool(dev->of_node, "wakeup-source");
> > > >  	device_init_wakeup(&pdev->dev, wakeup_source);
> > > > -	device_init_wakeup(&qcom->dwc3->dev, wakeup_source);
> > > 
> > > Surprisingly this part breaks wakeup on sc7x80, with the above removal
> > > of the device_may_wakeup() checks it is not clear to me why wakeup needs
> > > to be enabled for the core.
> > 
> > I can't explain that behaviour either. This change doesn't affect the
> > wakeup_path flag and genpd, and notably wakeup still works here with
> > sc8280xp.

> It turns out the dwc3 core wakeup flags are evaluated by:
> 
> 	int usb_phy_roothub_suspend(struct device *controller_dev,
> 	                            struct usb_phy_roothub *phy_roothub)
> 	{
> 		usb_phy_roothub_power_off(phy_roothub);
> 
> 		/* keep the PHYs initialized so the device can wake up the system */
> 		if (device_may_wakeup(controller_dev))
> 			return 0;
> 
> 		return usb_phy_roothub_exit(phy_roothub);
> 	}
> 
> 'controller_dev' is the dwc3 core. The root hub is un-initialized when wakeup is
> disabled. That causes wakeup to fail, and also happens to be the/one cause of
> the high power consumption of an onboard USB hub that I mentioned earlier in
> another thread.

Bah, I forgot about the USB core PHY management mess. This should be
disabled as the dwc3 driver manages the PHYs itself.

But because it currently enabled, the PHY was kept powered-on by USB
core (unless dropping device_init_wakeup()) and this indicates that that
is indeed needed for wakeup on your platform.

So this patch should be dropped, and I'll send a patch disabling the USB
core PHY management for dwc3 instead.

Johan