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

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Date:	Mon, 5 Aug 2013 16:40:42 +0200
From:	Benjamin Tissoires <benjamin.tissoires@...il.com>
To:	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

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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