Re: [PATCH 2/2] HID: hid-logitech-dj, querying_devices was never set

From: Benjamin Tissoires
Date: Mon Aug 05 2013 - 10:40:49 EST

On Mon, Aug 5, 2013 at 3:22 PM, Jiri Kosina <jkosina@xxxxxxx> 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.

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at