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, Bjørn Mork wrote:

> Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> writes:
> 
> > On Wed, 6 Apr 2016, 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.
> >> 
> >> Cc: <stable@xxxxxxxxxxxxxxx>
> >> Tested-by: Mike Murdoch <main.haarp@xxxxxxxxx>
> >> Signed-off-by: Mathias Nyman <mathias.nyman@xxxxxxxxxxxxxxx>
> >> ---
> >>  drivers/usb/host/xhci-hub.c | 6 ++++++
> >>  drivers/usb/host/xhci.c     | 1 +
> >>  2 files changed, 7 insertions(+)
> >> 
> >> diff --git a/drivers/usb/host/xhci-hub.c b/drivers/usb/host/xhci-hub.c
> >> index d61fcc4..7e8999a 100644
> >> --- a/drivers/usb/host/xhci-hub.c
> >> +++ b/drivers/usb/host/xhci-hub.c
> >> @@ -1289,12 +1289,18 @@ int xhci_bus_suspend(struct usb_hcd *hcd)
> >>  	__le32 __iomem **port_array;
> >>  	struct xhci_bus_state *bus_state;
> >>  	unsigned long flags;
> >> +	u32 status;
> >>  
> >>  	max_ports = xhci_get_ports(hcd, &port_array);
> >>  	bus_state = &xhci->bus_state[hcd_index(hcd)];
> >>  
> >>  	spin_lock_irqsave(&xhci->lock, flags);
> >>  
> >> +	/* Don't suspend root hub if there's an event pending. */
> >> +	status = readl(&xhci->op_regs->status);
> >> +	if (status & STS_EINT)
> >> +		return -EBUSY;
> >
> > Does anybody else see a problem here?
> 
> Like the EBUSY being propagated all the way to usb_suspend(), which is
> called on PMSG_HIBERNATE, PMSG_FREEZE and PMSG_SUSPEND?
> 
> This will not only prevent runtime suspend, but also system suspend,
> wont it?  Or did I miss something on the way?  The call chain between
> the USB dev_pm_ops .suspend and xhci_bus_suspend() is quite long..

I was thinking of returning with a private spinlock held.

Alan Stern


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