On 03.05.2018 14:37, Mathias Nyman wrote:
On 02.05.2018 20:52, Alan Stern wrote:
On Wed, 2 May 2018, Mathias Nyman wrote:
On 24.04.2018 16:50, Alan Stern wrote:
On Tue, 24 Apr 2018, Mathias Nyman wrote:
In this situation, the HCD_WAKEUP_PENDING(hcd) test in
hcd-pci.c:suspend_common() should prevent the controller from going
back into D3. The WAKEUP_PENDING bit gets set in
usb_hcd_resume_root_hub() and it doesn't get cleared until
hcd_bus_resume() runs.
I think xhci never calls usb_hcd_resume_root_hub() in xhci_resume() in this
specific failing case
xhci_resume() has a check:
/* Resume root hubs only when have pending events. */
status = readl(&xhci->op_regs->status);
if (status & STS_EINT) {
usb_hcd_resume_root_hub(xhci->shared_hcd);
usb_hcd_resume_root_hub(hcd);
}
If the check fails, then WAKEUP_PENDING bit is not set, and runtime PM
can suspend host controller again. when xhci driver finally gets to handle the interrupt
the controller may be in D3 already
This should only happen if xhci_resume() is called before xhci driver sees a pending interrupt,
could be possible as xhci has interrupt moderation enabled.
Then maybe that test should be removed. Calling
usb_hcd_resume_root_hub() for every wakeup shouldn't be too bad,
because there probably are not very many times when the controller gets
resumed without the root hub also being resumed.
The check was added to fix system suspend issue on a runtime suspended host:
commit d6236f6d1d885aa19d1cd7317346fe795227a3cc
xhci: Fix runtime suspended xhci from blocking system suspend.
The system suspend flow as following:
1, Freeze all user processes and kenrel threads.
2, Try to suspend all devices.
2.1, If pci device is in RPM suspended state, then pci driver will try
to resume it to RPM active state in the prepare stage.
2.2, xhci_resume function calls usb_hcd_resume_root_hub to queue two
workqueue items to resume usb2&usb3 roothub devices.
2.3, Call suspend callbacks of devices.
2.3.1, All suspend callbacks of all hcd's children, including
roothub devices are called.
2.3.2, Finally, hcd_pci_suspend callback is called.
Due to workqueue threads were already frozen in step 1, the workqueue
items can't be scheduled, and the roothub devices can't be resumed in
this flow. The HCD_FLAG_WAKEUP_PENDING flag which is set in
usb_hcd_resume_root_hub won't be cleared. Finally,
hcd_pci_suspend will return -EBUSY, and system suspend fails.
Hmmm. I don't recall seeing this problem occur with ehci-hcd. But
then, I haven't tested it very much recently.
We could change to a different work queue, one that doesn't get
frozen. But there's no guarantee that the work items would run before
your step 2.3.2.
Maybe we can avoid step 2.1. I think there have been some recent
changes to the PM code in this area. There may be a flag you can set
that will prevent the PCI core from resuming the host controller.
Or maybe we can change step 2.3.1, so that the root hub's suspend
callback will first do a resume if the WAKEUP_PENDING flag is set.
That might be the most reliable approach.
I'm not sure I understand the last suggestion, could you open up how it
would work?
Here's what I had in mind. See if you think this would work.
Consider choose_wakeup() in core/driver.c. That subroutine gets called
by usb_suspend() when step 2.3.1 wants to suspend a USB device. We
could patch it as follows:
Thanks, now I see.
I was able to reproduce system suspend failure of a runtime
suspended host by removing the event check in xhci_ring, and making sure
pm_runtime_resume(&udev->dev) wasn't called in choose_wakeup().
--- usb-4.x.orig/drivers/usb/core/driver.c
+++ usb-4.x/drivers/usb/core/driver.c
@@ -1449,11 +1449,21 @@ static void choose_wakeup(struct usb_dev
*/
w = device_may_wakeup(&udev->dev);
- /* If the device is autosuspended with the wrong wakeup setting,
+ /*
+ * If the device is autosuspended with the wrong wakeup setting,
* autoresume now so the setting can be changed.
+ *
+ * Likewise, if the device is an autosuspended root hub and the
+ * hcd needs to wake it up before the controller can be suspended,
+ * resume it now to clear the WAKEUP_PENDING flag.
*/
- if (udev->state == USB_STATE_SUSPENDED && w != udev->do_remote_wakeup)
- pm_runtime_resume(&udev->dev);
+ if (udev->state == USB_STATE_SUSPENDED) {
+ struct usb_hcd *hcd = bus_to_hcd(udev->bus);
+
+ if (w != udev->do_remote_wakeup ||
+ (!udev->parent && HCD_WAKEUP_PENDING(hcd)))
+ pm_runtime_resume(&udev->dev);
+ }
udev->do_remote_wakeup = w;
}
If I only add the:
if (!udev->parent && HCD_WAKEUP_PENDING(hcd)))
pm_runtime_resume(&udev->dev);
to choose_wakeup() It still doesn't work.
The HCD_WAKEUP_PENDING(hcd) check is false.
Turns out that the xhci_resume() that ends up setting HCD_FLAG_WAKEUP_PENDING is called
after choose_wakeup() for the roothub.
There's something in the pm functions order that I don't follow here
Actually I do get the ordering.
When everything is runtime suspended and start system suspend, we first suspend all
the usb devices, including the roothubs calling choose_wakeup() for the roothubs.
No flags are set yet. When pm continues suspending, and tries to suspend the xhci PCI
controller the PCI suspend code notices the device is runtime suspended,
it resumes it -> xhci_resume() -> usb_hcd_resume_root_hub() and WAKEUP_PENDING flag is set.
When PCI code then continues and tries to suspend the pci device it fails because the flag is set.
So checking HCD_WAKEUP_PENDING(hcd) for roothub in choose_wakeup() won't help, it's too early
-Mathias
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