Alan,
You were right, I think I have asked wrong question, so I changed the
subject as well.
>How does this happen? ehci-hcd doesn't use the rh_timer. It sets
>hcd->poll_rh to 0.
Actually the rh_timer is enabled by ehci_irq to process remote wakeup,
it's scheduled for 20ms delay.
/* remote wakeup [4.3.1] */
if (status & STS_PCD) {
......
mod_timer(&hcd->rh_timer, ehci->reset_done[i]);
}
> if (!HC_IS_RUNNING(hcd->state))
> return 0;
>That should prevent the routine from accessing any controller registers
if it is
>called after the root hub has been suspended.
You were right, the if statement should be sufficient. But in my code I
had this if statement commented out for a reason. So the question I
really should have asked is how to deal with the following situation:
Time0: Suspend one port - selective suspend. By calling ehci_control
with typeReq=SetPortFeature and wValue=USB_PORT_FEAT_SUSPEND;
Time1: Remote wakeup from device triggers an STS_PCD interrupt , handled
by ehci_irq;
Time2: The ISR falls into if (status & STS_PCD), at this moment EHCI is
still running (global suspend is expected to come shortly after
selective suspend), so usb_hcd_resume_root_hub doesn't get called;
Time3: In the while loop, since PORT_RESUME is set for the port being
waked up, rh_timer is set to fire 20ms later;
Time4: At the end of ehci_irq, usb_hcd_poll_rh_status is called, nothing
happens here because ehci_hub_status_data returns 0, reason being
time_after_eq(jiffies, ehci->reset_done) is false as ehci->reset_done
has been set to 20ms later in Time3;
Time5: EHCI is halted - global suspend scheduled by the host driver.
Time between Time0 and Time5 is about 20ms;
Time6: rh_timer fires. Time between Time3 and Time6 is 20ms (set in
ehci_irq). rh_timer_func -> usb_hcd_poll_rh_status ->
ehci_hub_status_data. Still nothing happens this time because
ehci_hub_status_data returns 0 again as it falls into the first if
statement if (!HC_IS_RUNNING(hcd->state)) (EHCI has been halted in
Time5, so hcd->state is SUSPENDED now).
The consequence is that the remote wakeup gets lost, the host doesn't
resume the bus as expected.
Thanks,
Fei
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