linux-kernel - Re: [PATCH 2/2] HID: hid-logitech-dj, querying

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Date:	Tue, 06 Aug 2013 23:03:33 +0200
From:	Sune Mølgaard <sune@...gaard.org>
To:	Benjamin Tissoires <benjamin.tissoires@...il.com>,
	Jiri Kosina <jkosina@...e.cz>
CC:	Nestor Lopez Casado <nlopezcasad@...itech.com>,
	Andrew de los Reyes <adlr@...omium.org>,
	joseph.salisbury@...onical.com,
	linux-input <linux-input@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] HID: hid-logitech-dj, querying_devices was never
 set

Being affected by this bug, I can confirm that Linux 3.11-rc4 still
exhibits the unwanted behaviour for me, but that commenting out the
single line from the second patch makes it work.

Thus, for requesting a revert on that line, you are most welcome to put
me down as a "Tested-By".

Best regards,

Sune Mølgaard

Benjamin Tissoires wrote:
> On Mon, Aug 5, 2013 at 3:22 PM, Jiri Kosina <jkosina@...e.cz> wrote:
>> On Fri, 2 Aug 2013, Benjamin Tissoires wrote:
>>
>>>> Could you please elaborate? (and put an elaborate description to revert
>>>> commit log perhaps?)
>>>
>>> Sure, so here is the revert commit log:
>>>
>>> --
>>>
>>> Commit "HID: hid-logitech-dj, querying_devices was never set" activate
>>> a flag which guarantees that we do not ask the receiver for too many
>>> enumeration. When the flag is set, each following enumeration call is
>>> discarded (the usb request is not forwarded to the receiver). The flag
>>> is then released when the driver receive a pairing information event,
>>> which normally follows the enumeration request.
>>> However, the USB3 bug makes the driver think the enumeration request
>>> has been forwarded to the receiver. However, it is actually not the
>>> case because the USB stack returns -EPIPE. So, when a new unknown
>>> device appears, the workaround consisting in asking for a new
>>> enumeration is not working anymore: this new enumeration is discarded
>>> because of the flag, which is never reset.
>>>
>>> A solution could be to trigger a timeout before releasing it, but for
>>> now, let's just revert the patch.
>>>
>>> --
>>
>> Thanks Benjamin.
>>
>> I'd like to have a bit more clarification about the USB3 bug, as this
>> whole issue is not completely clear to me.
>>
>> To be more specific -- when exactly do we receive -EPIPE, why do we
>> receive it and why do we not handle it properly?
> 
> Sure, I'll try (though the more I think of it, the more it seems
> blurry to me :( ).
> 
> So the initial probe function in hid-logitech-dj was implemented by
> using a direct call to hid_output_raw_report(). This call was
> synchronous, so we did get the -EPIPE return code. Then, the probe()
> function returns the -EPIPE error, cleaning the receiver and
> unregister it from the hid bus.
> 
> However, now, we use hid_hw_request(), which is asynchronous (from
> what I can read). At least, this code returns "void" as the set_report
> command seems to be scheduled for later handling. In usbhid, when the
> queue is flushed, I did not found a way to retrieve the error code...
> 
> So basically, the -EPIPE is received in usbhid_restart_ctrl_queue(),
> but nothing notifies hid-logitech-dj from the error. In the end, the
> probe() function returns without error code, but the receiver never
> received the notification.
> 
> Cheers,
> Benjamin
> --
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> 


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