Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753254AbcDFO4n (ORCPT ); Wed, 6 Apr 2016 10:56:43 -0400 Received: from mail-wm0-f68.google.com ([74.125.82.68]:35148 "EHLO mail-wm0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752361AbcDFO4k (ORCPT ); Wed, 6 Apr 2016 10:56:40 -0400 MIME-Version: 1.0 In-Reply-To: References: <1457372672-884-1-git-send-email-a.mathur@samsung.com> <56E17A73.8090901@bitmath.org> <20160401215128.GA5216@dtor-ws> Date: Wed, 6 Apr 2016 20:26:39 +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: 4721 Lines: 111 On Sat, Apr 2, 2016 at 10:31 PM, Aniroop Mathur wrote: > 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? > Hello Mr. Torokhov, Could you please update about this? It would be appreciating if you could help out to conclude it quickly. Thanks! > 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