Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752937AbcCJS5T (ORCPT ); Thu, 10 Mar 2016 13:57:19 -0500 Received: from mail-ob0-f174.google.com ([209.85.214.174]:33712 "EHLO mail-ob0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752551AbcCJS5A (ORCPT ); Thu, 10 Mar 2016 13:57:00 -0500 MIME-Version: 1.0 In-Reply-To: <56E17A73.8090901@bitmath.org> References: <1457372672-884-1-git-send-email-a.mathur@samsung.com> <56E17A73.8090901@bitmath.org> Date: Fri, 11 Mar 2016 00:26:57 +0530 Message-ID: Subject: Re: [PATCH] Input: Do not add SYN_REPORT in between a single packet data From: Aniroop Mathur To: Henrik Rydberg Cc: Dmitry Torokhov , Aniroop Mathur , "linux-input@vger.kernel.org" , lkml Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2188 Lines: 51 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. Thanks, Aniroop Mathur > Henrik >