linux-kernel - Re: [PATCH] Input: Do not add SYN_REPORT in between a single packet data

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Date:	Wed, 16 Mar 2016 23:54:54 +0530
From:	Aniroop Mathur <aniroop.mathur@...il.com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Henrik Rydberg <rydberg@...math.org>
Cc:	Aniroop Mathur <a.mathur@...sung.com>,
	"linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Input: Do not add SYN_REPORT in between a single packet data

Hello Mr. Torokhov,

Could you kindly help to update about this patch?

Thank you,
Aniroop Mathur


On Fri, Mar 11, 2016 at 12:26 AM, Aniroop Mathur
<aniroop.mathur@...il.com> wrote:
> Hi Henrik,
>
> On Thu, Mar 10, 2016 at 7:15 PM, Henrik Rydberg <rydberg@...math.org> 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
>>