Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754071AbcDAVvg (ORCPT ); Fri, 1 Apr 2016 17:51:36 -0400 Received: from mail-pf0-f179.google.com ([209.85.192.179]:34566 "EHLO mail-pf0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752482AbcDAVve (ORCPT ); Fri, 1 Apr 2016 17:51:34 -0400 Date: Fri, 1 Apr 2016 14:51:28 -0700 From: Dmitry Torokhov To: Aniroop Mathur Cc: Henrik Rydberg , Aniroop Mathur , "linux-input@vger.kernel.org" , lkml Subject: Re: [PATCH] Input: Do not add SYN_REPORT in between a single packet data Message-ID: <20160401215128.GA5216@dtor-ws> References: <1457372672-884-1-git-send-email-a.mathur@samsung.com> <56E17A73.8090901@bitmath.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2849 Lines: 61 On Fri, Mar 11, 2016 at 12:26:57AM +0530, Aniroop Mathur wrote: > Hi Henrik, > > On Thu, Mar 10, 2016 at 7:15 PM, Henrik Rydberg wrote: > > Hi Dmitry, > > > >>> diff --git a/drivers/input/input.c b/drivers/input/input.c > >>> index 8806059..262ef77 100644 > >>> --- a/drivers/input/input.c > >>> +++ b/drivers/input/input.c > >>> @@ -401,8 +401,7 @@ static void input_handle_event(struct input_dev *dev, > >>> if (dev->num_vals >= 2) > >>> input_pass_values(dev, dev->vals, dev->num_vals); > >>> dev->num_vals = 0; > >>> - } else if (dev->num_vals >= dev->max_vals - 2) { > >>> - dev->vals[dev->num_vals++] = input_value_sync; > >>> + } else if (dev->num_vals >= dev->max_vals - 1) { > >>> input_pass_values(dev, dev->vals, dev->num_vals); > >>> dev->num_vals = 0; > >>> } > >> > >> This makes sense to me. Henrik? > > > > I went through the commits that made these changes, and I cannot see any strong > > reason to keep it. However, this code path only triggers if no SYN events are > > seen, as in a driver that fails to emit them and consequently fills up the > > buffer. In other words, this change would only affect a device that is already, > > to some degree, broken. > > > > So, the question to Aniroop is: do you see this problem in practise, and in that > > case, for what driver? > > > > Nope. So far I have not dealt with any such driver. > I made this change because it is breaking protocol of SYN_REPORT event code. > > Further from the code, I could deduce that max_vals is just an estimation of > packet_size and it does not guarantee that packet_size is same as max_vals. > So real packet_size can be more than max_vals value and hence we could not > insert SYN_REPORT until packet ends really. > Further, if we consider that there exists a driver or will exist in future > which sets capability of x event code according to which max_value comes out to > y and the real packet size is z i.e. driver wants to send same event codes > again in the same packet, so input event reader would be expecting SYN_REPORT > after z events but due to current code SYN_REPORT will get inserted > automatically after y events, which is a wrong behaviour. Well, I think I agree with Aniroop that even if driver is to a degree broken we should not be inserting random SYN_REPORT events into the stream. I wonder if we should not add WARN_ONCE() there to highlight potential problems with the way we estimate the number of events. However I think there is an issue with the patch. If we happen to pass values just before the final SYN_REPORT sent by the driver then we reset dev->num_vals to 0 and will essentially suppress the final SYN_REPORT event, which is not good either. Thanks. -- Dmitry