Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752412AbcDBRBo (ORCPT ); Sat, 2 Apr 2016 13:01:44 -0400 Received: from mail-lf0-f68.google.com ([209.85.215.68]:33844 "EHLO mail-lf0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751334AbcDBRBl (ORCPT ); Sat, 2 Apr 2016 13:01:41 -0400 MIME-Version: 1.0 In-Reply-To: <20160401215128.GA5216@dtor-ws> References: <1457372672-884-1-git-send-email-a.mathur@samsung.com> <56E17A73.8090901@bitmath.org> <20160401215128.GA5216@dtor-ws> Date: Sat, 2 Apr 2016 22:31:39 +0530 Message-ID: Subject: Re: [PATCH] Input: Do not add SYN_REPORT in between a single packet data From: Aniroop Mathur To: Dmitry Torokhov Cc: Henrik Rydberg , 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: 4367 Lines: 101 Hello Mr. Torokhov, First of all, Thank you for your reply. On Sat, Apr 2, 2016 at 3:21 AM, Dmitry Torokhov wrote: > 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. > Yes, right! I think it can be fixed by sending the rest of events but not the last event in case number of events becomes greater than max_vals. The last event will be saved to be sent in next set of events. This way immediate SYN_REPORT will not be suppressed and duplicate SYN_REPORT event will not be sent as well. Change: @@ -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; - input_pass_values(dev, dev->vals, dev->num_vals); - dev->num_vals = 0; + } else if (dev->num_vals == dev->max_vals) { + input_pass_values(dev, dev->vals, dev->num_vals - 1); + dev->num_vals = 0; + dev->vals[dev->num_vals++] = dev->vals[dev->max_vals - 1]; } So, does the above patch looks good now? And may be about WARN_ONCE, do you mean to add something like below in above code? WARN_ONCE(1, "Packet did not complete yet but generally expected to be completed before generation of %d events.\n", dev->max_vals); Thanks, Aniroop Mathur > Thanks. > > -- > Dmitry