Re: [v15 2/6] usb: host: xhci-plat: Enable wakeup based on children wakeup status

[Pavan Kondeti <quic_pkondeti@quicinc.com>]

On Wed, May 11, 2022 at 08:54:25AM -0700, Matthias Kaehlcke wrote:
> On Wed, May 11, 2022 at 07:21:01AM +0530, Pavan Kondeti wrote:
> > On Mon, May 09, 2022 at 09:08:43AM +0530, Pavan Kondeti wrote:
> > > On Fri, May 06, 2022 at 08:36:31AM -0700, Matthias Kaehlcke wrote:
> > > > On Thu, May 05, 2022 at 02:26:09PM +0530, Krishna Kurapati wrote:
> > > > > device_wakeup_path() tells if any of the children devices needs
> > > > > wakeup. Use this hint to enable/disable wakeup of our device. This
> > > > > helps the parent device of xhci-plat (like sysdev) to retrieve
> > > > > the wakeup setting via device_wakeup_path().
> > > > > 
> > > > > Signed-off-by: Krishna Kurapati <quic_kriskura@quicinc.com>
> > > > > ---
> > > > >  drivers/usb/host/xhci-plat.c | 8 ++++++++
> > > > >  1 file changed, 8 insertions(+)
> > > > > 
> > > > > diff --git a/drivers/usb/host/xhci-plat.c b/drivers/usb/host/xhci-plat.c
> > > > > index 649ffd8..ad585fa 100644
> > > > > --- a/drivers/usb/host/xhci-plat.c
> > > > > +++ b/drivers/usb/host/xhci-plat.c
> > > > > @@ -415,6 +415,14 @@ static int __maybe_unused xhci_plat_suspend(struct device *dev)
> > > > >  	if (pm_runtime_suspended(dev))
> > > > >  		pm_runtime_resume(dev);
> > > > >  
> > > > > +	if (device_wakeup_path(dev)) {
> > > > > +		if (!device_may_wakeup(dev))
> > > > > +			device_wakeup_enable(dev);
> > > > > +	} else {
> > > > > +		if (device_may_wakeup(dev))
> > > > > +			device_wakeup_disable(dev);
> > > > > +	}
> > > > 
> > > > This code is not self-explantatory and deserves a comment.
> > > > 
> > > > Enabling/disabling wakeup for the purpose if signalling is a bit of a
> > > > hack. It might be an acceptable hack as long as it has no side effects.
> > > > However with the current implementation the wakeup state of the xHCI can
> > > > be different after resuming than it was before going to suspend:
> > > > 
> > > > after boot
> > > >   grep -h xhci /sys/class/wakeup/*/name
> > > >     => xhci-hcd.14.auto
> > > > 
> > > > after suspend w/o wakeup capable device
> > > >   grep -h xhci /sys/class/wakeup/*/name
> > > >     => no results
> > > > 
> > > > after suspend with wakeup capable device
> > > >   grep -h xhci /sys/class/wakeup/*/name
> > > >     => xhci-hcd.14.auto
> > > > 
> > > > The hack shouldn't alter the wakeup state 'persistently', i.e. you'll have
> > > > to restore it on resume, as in Pavan does in his reply to '[PATCH v14 2/7]
> > > > PM / wakeup: Add device_children_wakeup_capable()' (it needs to be done
> > > > conditionally though).
> > > 
> > > I am worried that we are not doing the right thing here. why should the
> > > xhci-plat goes against the wishes of the user space policy here? Can we NOT
> > > just do anything here? If some one wants xhci-plat to wakeup all the time,
> > > dwc3 will be configured to wakeup the system provided that the support is
> > > available. This way we don't break any existing users of xhci-plat i.e not
> > > enabling wakeup from the kernel.
> > > 
> > Krishna,
> > 
> > can we please drop this patch and use device_wakeup_path() and verify the
> > following cases.
> > 
> > 1. one of the downstream USB device supports wakeup and xhci-plat wakeup is enabled
> > 2. one of the downstream USB device supports wakeup and xhci-plat wakeup is
> > disabled
> > 3. none of the downstream USB device supports wakeup (or disable) and
> > xhci-plat wakeup is enabled.
> > 4. none of the downstream USB device supports wakeup (or disable) and
> > xhci-plat wakeup is disabled.
> 
> I wonder if we couldn't keep this simpler: if the dwc3 is wakeup capable keep
> the PHYs/core powered, otherwise power them down. Similar to what commit
> 689bf72c6e0d ("usb: dwc3: Don't reinitialize core during host
> bus-suspend/resume") intended, but with the additonal check for wakeup
> capability. We now know that the PHYs need to be powered down on some SoCs
> to allow the SoC to reach its low power mode during suspend:
> 
> 
>   commit c4a5153e87fdf6805f63ff57556260e2554155a5
>   Author: Manu Gautam <mgautam@codeaurora.org>
>   Date:   Thu Jan 18 16:54:30 2018 +0530
> 
>   usb: dwc3: core: Power-off core/PHYs on system_suspend in host mode
> 
>   Commit 689bf72c6e0d ("usb: dwc3: Don't reinitialize core during
>   host bus-suspend/resume") updated suspend/resume routines to not
>   power_off and reinit PHYs/core for host mode.
>   It broke platforms that rely on DWC3 core to power_off PHYs to
>   enter low power state on system suspend.
> 
> 
> With wakeup capable controllers this is apparently not an issue, otherwise
> the SoC wouldn't be able to enter its low power state when wakeup is
> enabled.

Agree to your suggestion. Thanks for your inputs.

Thanks,
Pavan