From mboxrd@z Thu Jan 1 00:00:00 1970 From: Benjamin Tissoires Subject: Re: [PATCH] HID: wacom: Stop mapping touch usages after processing HID_DG_CONTACTCOUNT Date: Tue, 12 Jul 2016 09:32:50 +0200 Message-ID: <20160712073250.GE4663@mail.corp.redhat.com> References: <20160711175950.17121-1-killertofu@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Return-path: Received: from mx1.redhat.com ([209.132.183.28]:50181 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750748AbcGLHcz (ORCPT ); Tue, 12 Jul 2016 03:32:55 -0400 Content-Disposition: inline In-Reply-To: <20160711175950.17121-1-killertofu@gmail.com> Sender: linux-input-owner@vger.kernel.org List-Id: linux-input@vger.kernel.org To: Jason Gerecke Cc: linux-input@vger.kernel.org, Ping Cheng , Aaron Skomra , Jason Gerecke Hi Jason, On Jul 11 2016 or thereabouts, Jason Gerecke wrote: > If a touchscreen contains both multitouch and single-touch reports in its > descriptor in that order, the driver may overwrite information it saved > about the format of the multitouch report. This can cause the report > processing code to get tripped up and send an incorrect event stream to > userspace. > > In particular, this can cause last_slot_field to be overwritten with the > result that the driver prematurely assumes it has finished processing a > slot and sending the ABS_MT_SLOT event at the wrong point in time, > associating events for the current contact with the following contact > instead. > > To prevent this from occuring, we stop mapping usages after having seen > HID_DG_CONTACTCOUNT. This usage is only present in multitouch reports, > so the format of any following single-touch reports will have no effect. I had a quick look at the driver, and it looks like the Cintiq Companion 2 has more than one multitouch collection (see 499522c "HID: wacom: Tie cached HID_DG_CONTACTCOUNT indices to report ID"). So if this doesn't break the cintiq companion 2, you have my reviewed-by, but I'd rather be sure (and please see if we really need to keep 499522c then). Cheers, Benjamin > > Signed-off-by: Jason Gerecke > --- > drivers/hid/wacom_wac.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/drivers/hid/wacom_wac.c b/drivers/hid/wacom_wac.c > index fcf2264..e499cdb 100644 > --- a/drivers/hid/wacom_wac.c > +++ b/drivers/hid/wacom_wac.c > @@ -1560,6 +1560,11 @@ static void wacom_wac_finger_usage_mapping(struct hid_device *hdev, > struct input_dev *input = wacom_wac->touch_input; > unsigned touch_max = wacom_wac->features.touch_max; > > + /* stop processing after the first multitouch report */ > + if (wacom_wac->hid_data.cc_report && > + wacom_wac->hid_data.cc_report != field->report->id) > + return; > + > switch (usage->hid) { > case HID_GD_X: > features->last_slot_field = usage->hid; > -- > 2.9.0 >