Date: Thu, 18 Jul 2013 15:09:36 -0700
From: Sarah Sharp <sarah.a.sharp@linux.intel.com>
To: Peter Hurley <peter@hurleysoftware.com>
Cc: Nestor Lopez Casado <nlopezcasad@logitech.com>, jkosina@suse.cz,
        benjamin.tissoires@gmail.com, adlr@chromium.org,
        joseph.salisbury@canonical.com, linux-input@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org
Subject: Re: [PATCH 1/2] Revert "Revert "HID: Fix logitech-dj: missing
 Unifying device issue""
Message-ID: <20130718220936.GA8025@xanatos>
References: <1374153691-25100-1-git-send-email-nlopezcasad@logitech.com>
 <51E84FD1.4050400@hurleysoftware.com>
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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 Sharp
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