On Tue, Mar 05, 2013 at 03:14:10PM -0800, Sarah Sharp wrote:
> > */
> > static void compliance_mode_recovery_timer_init(struct xhci_hcd *xhci)
> > {
> > + if (timer_pending(&xhci->comp_mode_recovery_timer)) {
> > + xhci_dbg(xhci, "Compliance Mode Recovery Timer already active.\n");
> > + return;
> > + }
> > +
> > xhci->port_status_u0 = 0;
> > init_timer(&xhci->comp_mode_recovery_timer);
>
> Isn't this racy? There's no locking here, so what if the timer fired
> just before the call to timer_pending happened? (The documentation on
> the timer interface doesn't describe whether timer_pending returns true
> if we're in the middle of a timer callback.)
Ah, yes. I think I misled Tony here. I thought the timer_pending() check
just checked to see if the timer was on the linked list, not realizing the
timer is removed from that list when executed. Instead I thought the
expires was set to -1 (or something large that it never expired) but it
stayed on the list.
We might have to dumb it down and just use a global init variable that is
set/cleared by the compliance functions with the assumption they are
called serially (as not to race).
Though this all seems very hackish and ugly. There has to be a better way
to do this.. :-(
>
> Also, looking at the compliance timer callback brings up further
> questions:
>
> static void compliance_mode_recovery(unsigned long arg)
> {
> ...
> for (i = 0; i < xhci->num_usb3_ports; i++) {
> temp = xhci_readl(xhci, xhci->usb3_ports[i]);
> if ((temp & PORT_PLS_MASK) == USB_SS_PORT_LS_COMP_MOD) {
> /*
> * Compliance Mode Detected. Letting USB Core
> * handle the Warm Reset
> */
>
> What happens when the xHCI host controller goes into D3cold due to
> runtime PM? The port status registers will read as all f's, so we will
> miss any transitions to the compliance mode that happened before or
> during the transition to D3cold.
>
> This code probably needs to wake up the host controller and keep it from
> suspending until all the ports can be read.
Fun... I take it there is no document that describes the various paths PM
can take during each of these phases?
Cheers,
Don
>
> Alan, would the right way to do that be a get/put call into the runtime
> PM core?
>
> Sarah Sharp
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