linux-kernel - Re: [PATCH v7 3/3] Input: add driver for the Hycon HY46XX touchpanel series

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Date:   Wed, 14 Apr 2021 13:22:55 +0200
From:   Giulio Benetti <giulio.benetti@...ettiengineering.com>
To:     Peter Hutterer <peter.hutterer@...-t.net>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     Rob Herring <robh@...nel.org>,
        Jonathan Neuschäfer <j.neuschaefer@....net>,
        Henrik Rydberg <rydberg@...math.org>,
        linux-input@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 3/3] Input: add driver for the Hycon HY46XX touchpanel
 series

Hi Peter, Dmitry,

On 4/14/21 8:46 AM, Peter Hutterer wrote:
> On Tue, Apr 13, 2021 at 10:44:07PM -0700, Dmitry Torokhov wrote:
>> Hi Giulio,
>>
>> On Tue, Apr 13, 2021 at 04:44:46PM +0200, Giulio Benetti wrote:
>>> +
>>> +	input_mt_report_pointer_emulation(tsdata->input, true);
>>
>> For touchscreens it does not make much sense to report BTN_DOUBLETAP,
>> BTN_TRIPLETAP, etc, events (they are really for touchpads), so I changed
>> this to
>>
>> 	input_mt_report_pointer_emulation(tsdata->input, false);
>>
>> to only report ABS_X, ABS_Y, and BTN_TOUCH, and applied.
> 
> Can you expand on this please, just to make sure I'm not misinterpreting
> those codes? Those bits are just for how many fingers are down (but without
> position), dropping those bits means you restrict the device to a pure
> single-touch screen. Or am I missing something here?

I've re-tested the driver after setting 
input_mt_report_pointer_emulation() use_count to false. It works 
correctly with all touch points expected. That use_count refers to 
finger count of Touchpad[1]. Also you can see that even with 
use_count=false this for loop[2] is entered by counting all the 
mt->slots and then input_event() reports all of them.

I hope I've understood correctly :-)

[1]: 
https://elixir.bootlin.com/linux/v5.12-rc7/source/drivers/input/input-mt.c#L190
[2]: 
https://elixir.bootlin.com/linux/v5.12-rc7/source/drivers/input/input-mt.c#L208

> then again, MT support has been in the kernel for long enough that by now
> everything should understand it, so there's a certain "meh" factor.
> 
> Cheers,
>     Peter
> 

Best regards
-- 
Giulio Benetti
Benetti Engineering sas