Input: resistive-adc-touch - fix division by zero error on z1 == 0

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>

diff --git a/drivers/input/touchscreen/resistive-adc-touch.c b/drivers/input/touchscreen/resistive-adc-touch.c
index 744544a..6f754a8 100644 (file)
--- 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, void *private)
                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))) {