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

[Nestor Lopez Casado]

Hi Sarah,

On Fri, Jul 19, 2013 at 12:09 AM, Sarah Sharp
<sarah.a.sharp@xxxxxxxxxxxxxxx> 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.

Could you re-phrase your question providing a bit more detail? I don't
quite get the idea.

>
> 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

Cheers,
Nestor
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