linux-kernel - Re: [PATCH v2] Input: touchscreen: ads7846.c: Fix race that causes missing releases

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Date:   Mon, 9 Nov 2020 12:00:28 +0100
From:   Oleksij Rempel <o.rempel@...gutronix.de>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Alexandru Ardelean <alexandru.ardelean@...log.com>
Cc:     David Jander <david@...tonic.nl>, kernel@...gutronix.de,
        linux-kernel@...r.kernel.org, linux-input@...r.kernel.org
Subject: Re: [PATCH v2] Input: touchscreen: ads7846.c: Fix race that causes
 missing releases

Hello Dmitry,

ping for this patch. Are there some changes needed?

Regards,
Oleksij

On Tue, Oct 27, 2020 at 11:54:16AM +0100, Oleksij Rempel wrote:
> From: David Jander <david@...tonic.nl>
> 
> If touchscreen is released while busy reading HWMON device, the release
> can be missed. The IRQ thread is not started because no touch is active
> and BTN_TOUCH release event is never sent.
> 
> Fixes: f5a28a7d4858f94a ("Input: ads7846 - avoid pen up/down when reading hwmon")
> Co-Developed-by: David Jander <david@...tonic.nl>
> Signed-off-by: David Jander <david@...tonic.nl>
> Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>
> ---
>  drivers/input/touchscreen/ads7846.c | 44 +++++++++++++++++------------
>  1 file changed, 26 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/input/touchscreen/ads7846.c b/drivers/input/touchscreen/ads7846.c
> index f2dc2c8ab5ec..4164a9834b59 100644
> --- a/drivers/input/touchscreen/ads7846.c
> +++ b/drivers/input/touchscreen/ads7846.c
> @@ -199,6 +199,26 @@ struct ads7846 {
>  #define	REF_ON	(READ_12BIT_DFR(x, 1, 1))
>  #define	REF_OFF	(READ_12BIT_DFR(y, 0, 0))
>  
> +static int get_pendown_state(struct ads7846 *ts)
> +{
> +	if (ts->get_pendown_state)
> +		return ts->get_pendown_state();
> +
> +	return !gpio_get_value(ts->gpio_pendown);
> +}
> +
> +static void ads7846_report_pen_up(struct ads7846 *ts)
> +{
> +	struct input_dev *input = ts->input;
> +
> +	input_report_key(input, BTN_TOUCH, 0);
> +	input_report_abs(input, ABS_PRESSURE, 0);
> +	input_sync(input);
> +
> +	ts->pendown = false;
> +	dev_vdbg(&ts->spi->dev, "UP\n");
> +}
> +
>  /* Must be called with ts->lock held */
>  static void ads7846_stop(struct ads7846 *ts)
>  {
> @@ -215,6 +235,10 @@ static void ads7846_stop(struct ads7846 *ts)
>  static void ads7846_restart(struct ads7846 *ts)
>  {
>  	if (!ts->disabled && !ts->suspended) {
> +		/* Check if pen was released since last stop */
> +		if (ts->pendown && !get_pendown_state(ts))
> +			ads7846_report_pen_up(ts);
> +
>  		/* Tell IRQ thread that it may poll the device. */
>  		ts->stopped = false;
>  		mb();
> @@ -606,14 +630,6 @@ static const struct attribute_group ads784x_attr_group = {
>  
>  /*--------------------------------------------------------------------------*/
>  
> -static int get_pendown_state(struct ads7846 *ts)
> -{
> -	if (ts->get_pendown_state)
> -		return ts->get_pendown_state();
> -
> -	return !gpio_get_value(ts->gpio_pendown);
> -}
> -
>  static void null_wait_for_sync(void)
>  {
>  }
> @@ -868,16 +884,8 @@ static irqreturn_t ads7846_irq(int irq, void *handle)
>  				   msecs_to_jiffies(TS_POLL_PERIOD));
>  	}
>  
> -	if (ts->pendown && !ts->stopped) {
> -		struct input_dev *input = ts->input;
> -
> -		input_report_key(input, BTN_TOUCH, 0);
> -		input_report_abs(input, ABS_PRESSURE, 0);
> -		input_sync(input);
> -
> -		ts->pendown = false;
> -		dev_vdbg(&ts->spi->dev, "UP\n");
> -	}
> +	if (ts->pendown && !ts->stopped)
> +		ads7846_report_pen_up(ts);
>  
>  	return IRQ_HANDLED;
>  }
> -- 
> 2.28.0
> 
> 

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