Re: Input sync flag when registering.

[Thomas Poussevin <thomas.poussevin@parrot.com>]

Le 25/08/2014 20:19, Dmitry Torokhov a écrit :
> Hi Thomas,
>
> On Mon, Aug 25, 2014 at 10:52:51AM +0200, Thomas Poussevin wrote:
>> Hi,
>> I noticed that with touchscreen drivers that don't explicitly call a
>> input_sync after input_register_device, suspend to ram is blocked if
>> no event is sent, because the input_dev created is considered as not
>> synchronized. The problem was seen with Atmel mxt driver. When any
>> event is sent, the driver explicitly ask a sync, so the problem is
>> solved.
>> The problem occurs only when the screen has never send any event
>> before suspend to ram.
>> I solved it setting the sync element to true (when input dev is
>> created, no element is pending).
>> Is there a better way to solve the problem ?
> It is not clear to me what the problem is. The kernel as far as I
> remember never checked state of 'sync' field when executing suspend
> callbacks. Moreover there is no longer 'sync' field at all in mainline.
>
> It sounds like some userspace code makes assumptions that are not always
> valid.
>
> Thanks.
>

Indeed, there is no longer 'sync' field in mainline. I realized i missed 
some commits, specifically  "Input: Send events one packet at a time" one.

Before theses commits, there used to be this problem, that is not 
relevant anymore :
It happened when Atmel mxt driver goes to suspend. mxt_stop func send a 
"input_sync" to mxt input device.
A input_sync has never been send before in input events.
The input_sync consists in : input_event(dev, EV_SYN, SYN_REPORT, 0);
In input_handle_event, if (!dev->sync) , then dev->sync = true; 
disposition = INPUT_PASS_TO_HANDLERS; . So finally there is a call to 
input_pass_event(dev, type, code, value);
But the input device created by mxt driver is allready suspending.
Suspend is canceled.

So i have 2 solutions (other than kernel update): either, in mxt driver, 
sending a input_sync after creating input device in order than the 
suspend sync call is not the first one (dev->sync will be true next 
time). Either, in the input driver, the default value of sync field is 
true (coherent with a just created device). I choosed this one.

Thanks.
Thomas.


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