On Thu, 4 Nov 2010, Maksim Rayskiy wrote:
> Hello,
>
> I am running into a crash on 2.6.36-rc7 kernel when I am bringing ohci
> controller out of suspend. Our suspend gates the clocks, so any access to
> the ohci registers becomes a bus error.
> I tracked the crash down to hcd polling function running off the timer. And
> it happens _before_ pm core calls our ohci resume method.
>
> #1 0x80310b84 in ohci_hub_status_data (hcd=<value optimized out>,
> buf=<value optimized out>)
> at drivers/usb/host/ohci-hub.c:520
> #2 0x802f11a0 in usb_hcd_poll_rh_status (hcd=<value optimized out>) at
> drivers/usb/core/hcd.c:675
> #3 0x8003faec in call_timer_fn (h=<value optimized out>) at
> kernel/timer.c:1057
> #4 __run_timers (h=<value optimized out>) at kernel/timer.c:1118
> #5 run_timer_softirq (h=<value optimized out>) at kernel/timer.c:1297
> #6 0x80038ff0 in __do_softirq () at kernel/softirq.c:219
> #7 0x80039140 in do_softirq () at kernel/softirq.c:266
> #8 0x800392d8 in irq_exit () at kernel/softirq.c:303
> #9 0x8000c35c in plat_irq_dispatch (regs=<value optimized out>) at
> arch/mips/brcmstb/irq.c:423
> #10 0x80001784 in ret_from_exception () at arch/mips/kernel/entry.S:34
>
> The simplest fix was to clear hcd->rh_pollable before going into suspend,
Drivers are not supposed to touch that flag. It is for use only by
usbcore.
> and restoring it after resume, but I am wondering if it is a known issue and
> there is a better solution to the problem.
This issue has not been reported before. Why didn't the
if (!HCD_HW_ACCESSIBLE(hcd))
goto done;
statements at the start of ohci_hub_status_data() prevent the unwanted
hardware accesses from occurring?
Admittedly, it might be a good idea to change this code to
if (!HCD_HW_ACCESSIBLE(hcd)) {
clear_bit(HCD_FLAG_POLL_RH, &hcd->flags);
goto done;
}
since there's no reason to continue polling if the hardware isn't
accessible.
Alan Stern
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