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SubjectRe: [linux-usb-devel] [PATCH] USB: consolidate error values from EHCI, UHCI and OHCI _suspend()
On Tue, 19 Sep 2006, Jiri Kosina wrote:

> On Mon, 18 Sep 2006, David Brownell wrote:
> > > EHCI, UHCI and OHCI USB host drivers are not consistent when returining
> > > error values from their _suspend() functions, in case that the device is
> > > not in suspended state. This could confuse users, so let all three of them
> > > return -EBUSY.
> > Shouldn't you also update uhci_suspend()? Currently it just ignores
> > hcd->state ...
> You are right that the patch is possibly not fully correct. I was trying
> to fix the situation I was getting into with the bug in usb_resume_both()
> (see my "[PATCH] 2.6.18-rc6-mm2 - usb_resume_both() - fix suspend/resume"
> mail from yesterday), but now it is obvious that the EINVAL from UHCI is
> of a "different kind" than EBUSY from OHCI and UHCI (though they are
> triggered in the same situations -- when the previous resume was not done
> correctly).

Sort of. The real trigger is that the PM core tries to suspend the
upper-level PCI device but the lower-level root-hub device has not been
suspended. You saw this occurring because during the previous resume, the
root-hub device's power.power_state.event was not updated, causing the PM
core to think the root hub was still suspended when in fact it wasn't.

> As far as I can see, the UHCI driver is, strangely enough, not using
> hcd->state at all.
> (by the way, EHCI and OHCI seem to have broken (read: missing) locking
> when accessing the hcd->state. Should I fix it by per-hcd spinlock, or
> does the patch already exist somewhere?)

Believe it or not, these two paragraphs are closely connected. The reason
uhci-hcd doesn't use hcd->state at all is because there is no locking to
protect it!

My feeling has long been that hcd->state deserves to disappear. It tries
to serve too many functions. Please don't add any code in a futile
attempt to preserve it.

Alan Stern

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