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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 <johannes.kirchmair@skidata.com>
Link: https://lore.kernel.org/r/20250129-fix_tsc_calculation_overflow-v2-1-9e51333496ad@skidata.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
This commit is contained in:
Johannes Kirchmair 2025-01-29 14:51:20 +01:00 committed by Dmitry Torokhov
parent d504bbda8c
commit 9a12e2fb3f
1 changed files with 6 additions and 3 deletions
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9
drivers/input/touchscreen/tsc2007_core.c
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@ -23,6 +23,7 @@
#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>
@ -68,7 +69,7 @@ static void tsc2007_read_values(struct tsc2007 *tsc, struct ts_event *tc)
u32 tsc2007_calculate_resistance(struct tsc2007 *tsc, struct ts_event *tc)
{
u32 rt = 0;
u64 rt = 0;
/* range filtering */
if (tc->x == MAX_12BIT)
@ -79,11 +80,13 @@ u32 tsc2007_calculate_resistance(struct tsc2007 *tsc, struct ts_event *tc)
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)