On Wed, 18 Apr 2007, Johannes Berg wrote:
> Hi,
>
> Here's something I just observed yesterday. At first I was blaming my
> suspend changes for powerpc since I can't make it happen without them,
> but I've gone back and forth over them and can't find the problem, so
> while I'm still not sure they aren't at fault I wanted some input from
> the USB side.
>
> What happens is that apparently for whatever (legitimate or not) reason
> right before suspend the rh_timer in hcd.c gets scheduled but never runs
> before suspend. Then during resume, when IRQs are enabled, it gets to
> run, but the device hasn't been resumed yet.
>
> So what happens then is that in rh_timer usb_hcd_poll_rh_status is
> called and calls (indirectly) ohci_hub_status_data which errors out in
> line 431:
>
> 430: /* init status */
> 431: if (roothub_status (ohci) & (RH_HS_LPSC | RH_HS_OCIC))
> 432: buf [0] = changed = 1;
>
> for the obvious reason that roothub_status() can't actually access the
> registers yet. I suspect this can also happen on x86 but that just
> returns 0xffffffff on the read and not much more happens. Or powermac
> really is special because we have a hook to turn off the USB asic.
>
> Now, since I mentioned a timer timing clearly has an influence :) But
> the odd thing is that it happens fairly consistently when I suspend from
> the console right after boot, while it never happens when suspending
> from within X (or even from the console when I'm logged in in X). Maybe
> suspend is so much slower from X that the timer fires before the machine
> is suspended or something.
>
> It seems to me that the timer shouldn't be scheduled when we go into
> suspend, but I'll leave the proper fix up to somebody else. Unless of
> course my suspend changes do indeed have a bug somewhere (I sure hope
> not), unfortunately I haven't been able to trigger this on an unpatched
> kernel. But I haven't tried very hard either.
The comparable routine in uhci-hcd includes this code:
if (!test_bit(HCD_FLAG_HW_ACCESSIBLE, &hcd->flags) || uhci->dead)
goto done;
and likewise, ehci_hub_status_data() includes this:
if (!HC_IS_RUNNING(hcd->state))
return 0;
Something similar needs to be added in ohci-hub.c. Does the patch below
fix your problem?
Alan Stern
Index: usb-2.6/drivers/usb/host/ohci-hub.c
===================================================================
--- usb-2.6.orig/drivers/usb/host/ohci-hub.c
+++ usb-2.6/drivers/usb/host/ohci-hub.c
@@ -417,6 +417,8 @@ ohci_hub_status_data (struct usb_hcd *hc
unsigned long flags;
spin_lock_irqsave (&ohci->lock, flags);
+ if (!test_bit(HCD_FLAG_HW_ACCESSIBLE, &hcd->flags))
+ goto done;
/* undocumented erratum seen on at least rev D */
if ((ohci->flags & OHCI_QUIRK_AMD756)
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