Re: [PATCH 1/2] Revert "Revert "HID: Fix logitech-dj: missing Unifyingdevice issue""

[Peter Hurley]

On 07/18/2013 06:09 PM, Sarah Sharp wrote:
> On Thu, Jul 18, 2013 at 04:28:01PM -0400, Peter Hurley wrote:
> > [ +cc Sarah Sharp, linux-usb ]
> >
> > On 07/18/2013 09:21 AM, Nestor Lopez Casado wrote:
> > > This reverts commit 8af6c08830b1ae114d1a8b548b1f8b056e068887.
> > >
> > > This patch re-adds the workaround introduced by 596264082f10dd4
> > > which was reverted by 8af6c08830b1ae114.
> > >
> > > The original patch 596264 was needed to overcome a situation where
> > > the hid-core would drop incoming reports while probe() was being
> > > executed.
> > >
> > > This issue was solved by c849a6143bec520af which added
> > > hid_device_io_start() and hid_device_io_stop() that enable a specific
> > > hid driver to opt-in for input reports while its probe() is being
> > > executed.
> > >
> > > Commit a9dd22b730857347 modified hid-logitech-dj so as to use the
> > > functionality added to hid-core. Having done that, workaround 596264
> > > was no longer necessary and was reverted by 8af6c08.
> > >
> > > We now encounter a different problem that ends up 'again' thwarting
> > > the Unifying receiver enumeration. The problem is time and usb controller
> > > dependent. Ocasionally the reports sent to the usb receiver to start
> > > the paired devices enumeration fail with -EPIPE and the receiver never
> > > gets to enumerate the paired devices.
> > >
> > > With dcd9006b1b053c7b1c the problem was "hidden" as the call to the usb
> > > driver became asynchronous and none was catching the error from the
> > > failing URB.
> > >
> > > As the root cause for this failing SET_REPORT is not understood yet,
> > > -possibly a race on the usb controller drivers or a problem with the
> > > Unifying receiver- reintroducing this workaround solves the problem.
> >
> >
> > Before we revert to using the workaround, I'd like to suggest that
> > this new "hidden" problem may be an interaction with the xhci_hcd host
> > controller driver only.
> >
> > Looking at the related bug, the OP indicates the machine only has
> > USB3 ports. Additionally, comments #7, #100, and #104 of the original
> > bug report [1] add additional information that would seem to confirm
> > this suspicion.
>
> Question: does this USB device need a control transfer to reset its
> endpoints when the endpoints are not actually halted?  If so, yes, that
> is a known xHCI driver bug that needs to be fixed.  The xHCI host will
> not accept a Reset Endpoint command when the endpoints are not actually
> halted, but the USB core will send the control transfer to reset the
> endpoint.  That means the device and host toggles will be out of sync,
> and all messages will start to fail with -EPIPE.
>
> Can the OP capture a usbmon trace when the device starts failing?  That
> will reveal whether this actually is the issue.  dmesg output with
> CONFIG_USB_DEBUG and CONFIG_USB_XHCI_HCD_DEBUGGING turned on would also
> be helpful.

Sarah,

I forwarded your usbmon capture request to the OP in the bug report
(I don't have an email address for the reporter).

As far as getting printk output from a custom kernel, I think that may
be beyond the reporter's capability. Perhaps one of the Ubuntu devs
triaging this bug could provide a test kernel for the OP with those
options on.

Joseph, would you be willing to do that?

Regards,
Peter Hurley
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