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

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Message-Id: <20201027105416.18773-1-o.rempel@pengutronix.de>
Date:   Tue, 27 Oct 2020 11:54:16 +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>,
        Oleksij Rempel <o.rempel@...gutronix.de>,
        kernel@...gutronix.de, linux-kernel@...r.kernel.org,
        linux-input@...r.kernel.org
Subject: [PATCH v2] Input: touchscreen: ads7846.c: Fix race that causes missing releases

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