Re: [PATCH 3/7] xhci: Don't suspend a xhci usb bus if there is a pending event.

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On Wed, 6 Apr 2016, Greg KH wrote:

> On Wed, Apr 06, 2016 at 04:08:04PM +0300, Mathias Nyman wrote:
> > We don't want to runtime suspend a bus if there is an event pending.
> > The roothub on a NEC uPD720200 host with a single USB3 device connected
> > might go back to runtime suspend immediately after runtime resume as
> > hub might not yet see any port changes in resume.
> > 
> > Prevent this by checking if there is a unhandled event pending when
> > calling runtime suspend.
> 
> As Alan points out, you didn't actually test this :(

Also as Björn pointed out, failing a system suspend isn't a good idea.  
In general, you should do it only if wakeup is enabled and there is a 
pending wakeup event.

In this case there may be alternatives.  For example, you could just 
delay a few ms until the pending event has been handled.  Or, if you 
really just want to prevent runtime suspend, you should check to see if 
this was a runtime suspend and not a system suspend.  Or you could 
prevent the bus from being runtime suspended in the first place by 
doing a pm_runtime_get_sync().

Alan Stern

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