Hello,
just a friendly ping :-)
Best regards Johannes
> -----Ursprüngliche Nachricht-----
> Von: mailinglist1@xxxxxxxxxxxxxxxxxxxx
> <mailinglist1@xxxxxxxxxxxxxxxxxxxx>
> Gesendet: Mittwoch, 29. Jänner 2025 14:51
> An: Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx>
> Cc: linux-input@xxxxxxxxxxxxxxx; Johannes Kirchmair - SKIDATA
> <johannes.kirchmair@xxxxxxxxxxx>
> Betreff: [PATCH v2] tsc2007: prevent overflow in pressure calculation
>
> Caution: This is an external email, please take care when clicking links or
> opening attachments
>
> From: Johannes Kirchmair <johannes.kirchmair@xxxxxxxxxxx>
>
> The touch resistance calculation in the tsc2007 driver is prone to overflow if
> (z2 - z1) is large and also x is reasonably big. As an result the driver
> sometimes emit input events even with very little touch pressure applied. For
> those events the x and y coordinates can be substantially off. We fix the
> overflow problematic by calculating in a bigger int type.
>
> Signed-off-by: Johannes Kirchmair <johannes.kirchmair@xxxxxxxxxxx>
> ---
> Changes in v2:
> - removed brackets that slipped in
> - use div_u64
> ---
> drivers/input/touchscreen/tsc2007_core.c | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/input/touchscreen/tsc2007_core.c
> b/drivers/input/touchscreen/tsc2007_core.c
> index 8d832a372b89..0b5934d843b9 100644
> --- a/drivers/input/touchscreen/tsc2007_core.c
> +++ b/drivers/input/touchscreen/tsc2007_core.c
> @@ -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)
>
> ---
> base-commit: 05dbaf8dd8bf537d4b4eb3115ab42a5fb40ff1f5
> change-id: 20250129-fix_tsc_calculation_overflow-90860d4e3492
>
> Best regards,
> --
> Johannes Kirchmair <johannes.kirchmair@xxxxxxxxxxx>
