Input: ads7846 - fix race that causes missing releases

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: f5a28a7d ("Input: ads7846 - avoid pen up/down when reading hwmon")
Co-developed-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: David Jander <david@protonic.nl>
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Link: https://lore.kernel.org/r/20201027105416.18773-1-o.rempel@pengutronix.deSigned-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

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;
 }