[PATCH 5.14 081/151] Input: resistive-adc-touch - fix division by zero error on z1 == 0

Greg Kroah-Hartman
2021-10-18T13:55:46Z

From: Oleksij Rempel <o.rempel@pengutronix.de>

commit fe0a7e3d012738b0034b3c97ddb0e8bc0a3ff0e6 upstream.

For proper pressure calculation we need at least x and z1 to be non
zero. Even worse, in case z1 we may run in to division by zero
error.

Fixes: 60b7db914ddd ("Input: resistive-adc-touch - rework mapping of channels")
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Link: https://lore.kernel.org/r/20211007095727.29579-1-o.rempel@pengutronix.de
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/input/touchscreen/resistive-adc-touch.c | 29 +++++++++++++-----------
1 file changed, 16 insertions(+), 13 deletions(-)

--- a/drivers/input/touchscreen/resistive-adc-touch.c
+++ b/drivers/input/touchscreen/resistive-adc-touch.c
@@ -71,19 +71,22 @@ static int grts_cb(const void *data, voi
unsigned int z2 = touch_info[st->ch_map[GRTS_CH_Z2]];
unsigned int Rt;

- Rt = z2;
- Rt -= z1;
- Rt *= st->x_plate_ohms;
- Rt = DIV_ROUND_CLOSEST(Rt, 16);
- Rt *= x;
- Rt /= z1;
- Rt = DIV_ROUND_CLOSEST(Rt, 256);
- /*
- * On increased pressure the resistance (Rt) is decreasing
- * so, convert values to make it looks as real pressure.
- */
- if (Rt < GRTS_DEFAULT_PRESSURE_MAX)
- press = GRTS_DEFAULT_PRESSURE_MAX - Rt;
+ if (likely(x && z1)) {
+ Rt = z2;
+ Rt -= z1;
+ Rt *= st->x_plate_ohms;
+ Rt = DIV_ROUND_CLOSEST(Rt, 16);
+ Rt *= x;
+ Rt /= z1;
+ Rt = DIV_ROUND_CLOSEST(Rt, 256);
+ /*
+ * On increased pressure the resistance (Rt) is
+ * decreasing so, convert values to make it looks as
+ * real pressure.
+ */
+ if (Rt < GRTS_DEFAULT_PRESSURE_MAX)
+ press = GRTS_DEFAULT_PRESSURE_MAX - Rt;
+ }
}

if ((!x && !y) || (st->pressure && (press < st->pressure_min))) {