linux-kernel - Re: [PATCH] HID: usbhid: prevent unwanted events to be sent when re-opening the device

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Date:	Wed, 29 Oct 2014 11:05:28 +0100 (CET)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Benjamin Tissoires <benjamin.tissoires@...hat.com>
cc:	Hans de Goede <hdegoede@...hat.com>,
	Bastien Nocera <hadess@...ess.net>,
	linux-kernel@...r.kernel.org, linux-input@...r.kernel.org
Subject: Re: [PATCH] HID: usbhid: prevent unwanted events to be sent when
 re-opening the device

On Tue, 30 Sep 2014, Benjamin Tissoires wrote:

> When events occurs while no one is listening to the node (hid->open == 0
> and usb_kill_urb() called) some events are still stacked somewhere in
> the USB (kernel or device?) stack. When the node gets reopened, these
> events are drained, and this results in spurious touch down/up, or mouse
> button clicks.
> 
> The problem was spotted with touchscreens in fdo bug #81781 [1], but it
> actually occurs with any mouse using hid-generic or touchscreen.
> 
> A way to reproduce it is to call:
> 
> $ xinput disable 9 ; sleep 5 ; xinput enable 9
> 
> With 9 being the device ID for the touchscreen/mouse. During the "sleep",
> produce some touch events or click events. When "xinput enable" is called,
> at least one click is generated.
> 
> This patch tries to fix this by draining the queue for 50 msec and
> during this time frame, not forwarding these old events to the hid layer.
> 
> Hans completed the explanation:
> """
> Devices like mice (basically any hid device) will have a fifo
> on the device side, when we stop submitting urbs to get hid reports from
> it, that fifo will fill up, and when we resume we will get whatever
> is there in that fifo.
> """
> 
> [1] https://bugs.freedesktop.org/show_bug.cgi?id=81781
> 
> Signed-off-by: Benjamin Tissoires <benjamin.tissoires@...hat.com>
> ---
> 
> OK, I know this is uggly, but I could not find a better way :(

I have been thinking about this quite a lot, but unfortunately wasn't able 
to come up with anything better either, so I am queuing this now.

Thanks.

-- 
Jiri Kosina
SUSE Labs
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