linux-kernel - Re: [PATCH] Input: MT - add input sync to refresh touch points after screen locked

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Message-ID: <3c3bry7uq4njh7bzldjiabf46u3dupzc4odispwrlpmhilj4cr@kieoev2hjkac>
Date: Mon, 28 Apr 2025 09:45:11 -0700
From: Dmitry Torokhov <dmitry.torokhov@...il.com>
To: Ai Chao <aichao@...inos.cn>
Cc: rydberg@...math.org, linux-input@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Input: MT - add input sync to refresh touch points after
 screen locked

Hi,

On Sun, Apr 27, 2025 at 10:12:03AM +0800, Ai Chao wrote:
> If the touchscreen support ten-figers press it to lock touchscreen. When
> the touchscreen is locked, the ABS_MT_TRACKING_ID event remains
> buffered. We need to used input-sync to refresh the event buffer.

I am sorry but I do not follow what you are trying to say. However I can
tell for sure that issuing "sync" each time a finger is lifted off the
touchpad or touchscreen is not the right thing to do and will interfere
with frame handling and dropping unused contacts that is employed by
many drivers. Drivers should issue "sync" when they are done reporting
device state.

> 
> Signed-off-by: Ai Chao <aichao@...inos.cn>
> ---
>  drivers/input/input-mt.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/input/input-mt.c b/drivers/input/input-mt.c
> index 337006dd9dcf..659d752ca830 100644
> --- a/drivers/input/input-mt.c
> +++ b/drivers/input/input-mt.c
> @@ -147,6 +147,7 @@ bool input_mt_report_slot_state(struct input_dev *dev,
>  
>  	if (!active) {
>  		input_event(dev, EV_ABS, ABS_MT_TRACKING_ID, -1);
> +		input_sync(dev);
>  		return false;
>  	}
>  

Thanks.

-- 
Dmitry