Re: [PATCH 2/2] usb: host: xhci-plat: add wakeup entry at /sys

[Peter Chen <peter.chen@nxp.com>]

On 20-07-04 10:48:16, Alan Stern wrote:
> On Sat, Jul 04, 2020 at 09:22:45AM +0000, Peter Chen wrote:
> > On 20-07-03 10:19:11, Alan Stern wrote:
> > > On Fri, Jul 03, 2020 at 02:25:32PM +0800, Peter Chen wrote:
> > > > After that, the user could enable controller as wakeup source
> > > > for system suspend through /sys entry.
> > > > 
> > > > Signed-off-by: Peter Chen <peter.chen@nxp.com>
> > > > ---
> > > >  drivers/usb/host/xhci-plat.c | 2 +-
> > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > > 
> > > > diff --git a/drivers/usb/host/xhci-plat.c b/drivers/usb/host/xhci-plat.c
> > > > index cebe24ec80a5..bb5d73f0a796 100644
> > > > --- a/drivers/usb/host/xhci-plat.c
> > > > +++ b/drivers/usb/host/xhci-plat.c
> > > > @@ -287,7 +287,7 @@ static int xhci_plat_probe(struct platform_device *pdev)
> > > >  		*priv = *priv_match;
> > > >  	}
> > > >  
> > > > -	device_wakeup_enable(hcd->self.controller);
> > > > +	device_set_wakeup_capable(hcd->self.controller, true);
> > > 
> > > 
> > > In fact both this patch and the original code are wrong.  It really should 
> > > be:
> > > 
> > > 	device_init_wakeup(hcd->self.controller, true);
> > > 
> > > This will add the wakeup entry in sysfs and set it to Enabled.  This is 
> > > the appropriate behavior, as explained in the kerneldoc for 
> > > device_init_wakeup().  The reason is because the controller device doesn't 
> > > create any wakeup events on its own; it merely relays wakeup requests from 
> > > descendant devices (root hubs or USB devices).
> > 
> > Hi Alan,
> > 
> > At xhci-plat.c's system suspend API xhci_plat_suspend, it depends on
> > power/wakeup value to determine whether the controller should enable
> > port wakeup capabilities, and from the system level, whether the system
> > supports USB wakeup or not is better to be determined by user, and is
> > disabled by default.
> > 
> > Yes, you are right. The wakeup events are from controller's descendant
> > devices, and it is better to use roothub's wakeup capability to control
> > portsc's wakeup setting. At controller driver, the meaning for wakeup
> > setting is enabling wakeup interrupt for hardware signal events (dp/dm for USB2,
> > and RX-detect for USB3), this hardware logic is the glue layer and
> > designed by each vendors, without this logic, the USB controller can't
> > be woken up due to the USBCMD.RS bit is cleared, and there is no
> > standard EHCI or xHCI interrupt. The controller's wakeup setting is
> > better to be disabled by default, and decided by user too.
> > 
> > For me, either this patch or use roothub's wakeup capability to
> > control portsc wakeup setting, both are OK. Mathias, what's your
> > opinion?
> 
> Mathias is starting a long vacation, so he might not reply for a while.
> 
> Note that hcd-pci.c, ohci-platform.c, and ehci-platform.c all call 
> device_wakeup_enable().  This indicates that xhci-plat.c should do the 
> same -- presumably device_set_wakeup_capable() is already called somewhere 
> in the platform-specific code.
> 

Thanks for the information, Alan.

I could not understand why device_wakeup_enable is used in these device
drivers? At Documentation/driver-api/pm/devices.rst, L189, it also says:

	during a system sleep transition.  Device drivers, however, are
       	not expected to call :c:func:`device_set_wakeup_enable()` directly
       	in any case.

-- 

Thanks,
Peter Chen