Input: tsc2007 - prevent overflow in pressure calculation

The touch resistance calculation in the tsc2007 driver is prone to
overflow if (z2 - z1) is large and also x is reasonably big. This
overflow results in the driver emitting input events when very little
touch pressure is applied. In these events the x and y coordinates can
be substantially off.

Avoid the overflow by using u64 when calculating resistance value.

Signed-off-by: Johannes Kirchmair <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Dmitry Torokhov <[e-mail]>

drivers/input/touchscreen/tsc2007_core.c

···
 #include <linux/input.h>
 #include <linux/interrupt.h>
 #include <linux/i2c.h>
+#include <linux/math64.h>
 #include <linux/mod_devicetable.h>
 #include <linux/property.h>
 #include <linux/platform_data/tsc2007.h>
···
 
 u32 tsc2007_calculate_resistance(struct tsc2007 *tsc, struct ts_event *tc)
 {
-	u32 rt = 0;
+	u64 rt = 0;
 
 	/* range filtering */
 	if (tc->x == MAX_12BIT)
···
 		rt = tc->z2 - tc->z1;
 		rt *= tc->x;
 		rt *= tsc->x_plate_ohms;
-		rt /= tc->z1;
+		rt = div_u64(rt, tc->z1);
 		rt = (rt + 2047) >> 12;
 	}
 
-	return rt;
+	if (rt > U32_MAX)
+		return U32_MAX;
+	return (u32) rt;
 }
 
 bool tsc2007_is_pen_down(struct tsc2007 *ts)