Re: [PATCH v9 2/5] usb: dwc3: core: Host wake up support from system suspend

[Matthias Kaehlcke <mka@chromium.org>]

On Tue, Nov 16, 2021 at 04:28:16PM -0800, Brian Norris wrote:
> On Mon, Nov 01, 2021 at 01:23:41PM +0530, Sandeep Maheswaram wrote:
> > Avoiding phy powerdown when wakeup capable devices are connected
> > by checking wakeup property of xhci plat device.
> > Phy should be on to wake up the device from suspend using wakeup capable
> > devices such as keyboard and mouse.
> > 
> > Signed-off-by: Sandeep Maheswaram <quic_c_sanm@quicinc.com>
> 
> Because you've now factored in a device_may_wakeup() (which evaluates
> 'false' for me), this no longer breaks my Rockchip RK3399 systems
> (previous versions did). So from that angle:
> 
> Tested-by: Brian Norris <briannorris@chromium.org>
> 
> > ---
> >  drivers/usb/dwc3/core.c | 7 +++++--
> >  1 file changed, 5 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
> > index 643239d..a6ad0ed 100644
> > --- a/drivers/usb/dwc3/core.c
> > +++ b/drivers/usb/dwc3/core.c
> > @@ -1787,7 +1787,7 @@ static int dwc3_suspend_common(struct dwc3 *dwc, pm_message_t msg)
> >  		dwc3_core_exit(dwc);
> >  		break;
> >  	case DWC3_GCTL_PRTCAP_HOST:
> > -		if (!PMSG_IS_AUTO(msg)) {
> > +		if (!PMSG_IS_AUTO(msg) && !device_may_wakeup(&dwc->xhci->dev)) {
> 
> I still find it odd to use device_may_wakeup(), since that's something
> controlled by user space (sysfs) and doesn't fully factor in hardware
> support. But that's what xhci-plat.c is doing, so I guess I see why
> you're imitating it...
> ...still, feels wrong to me. But so does a lot of how dwc3 works.

device_may_wakeup() actually factors in hardware support, at least if the
driver does the right thing (TM). The (current) implementation is:

static inline bool device_may_wakeup(struct device *dev)
{
	return dev->power.can_wakeup && !!dev->power.wakeup;
}

'.can_wakeup' should describe the hardware capability to wake up and the
other flag whether wakeup is enabled (which can be altered by userspace).

What this series currently does with the .can_wakeup flag is still wrong
though IMO. Patch "[1/5] usb: host: xhci: plat: Add suspend quirk for dwc3
controller" [1] dynamically sets the flag with a value that depends on what
is connected to the bus, so it doesn't specify any longer whether the
hardware supports wakeup or not.

[1] https://patchwork.kernel.org/project/linux-usb/patch/1635753224-23975-2-git-send-email-quic_c_sanm@quicinc.com/