[ Upstream commit 820830ec91 ]
In some rare cases the 32 bit Rt value will overflow if z2 and x is max,
z1 is minimal value and x_plate_ohms is relatively high (for example 800
ohm). This would happen on some screen age with low pressure.
There are two possible fixes:
- make Rt 64bit
- reorder calculation to avoid overflow
The second variant seems to be preferable, since 64 bit calculation on
32 bit system is a bit more expensive.
Fixes: ffa458c1bd ("spi: ads7846 driver")
Co-developed-by: David Jander <david@protonic.nl>
Signed-off-by: David Jander <david@protonic.nl>
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Link: https://lore.kernel.org/r/20201113112240.1360-1-o.rempel@pengutronix.de
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
4ea501f332