https://github.com/torvalds/linux
Revision 227a3a2fc31d8e4bb9c88d4804e19530af245b1b authored by Eliav Farber on 08 September 2022, 15:24:32 UTC, committed by Guenter Roeck on 08 September 2022, 18:55:24 UTC
According to Moortec Embedded Voltage Monitor (MEVM) series 3 data sheet, the minimum input signal is -100mv and maximum input signal is +1000mv. The equation used to convert the digital word to voltage uses mixed types (*val signed and n unsigned), and on 64 bit machines also has different size, since sizeof(u32) = 4 and sizeof(long) = 8. So when measuring a negative input, n will be small enough, such that PVT_N_CONST * n < PVT_R_CONST, and the result of (PVT_N_CONST * n - PVT_R_CONST) will overflow to a very big positive 32 bit number. Then when storing the result in *val it will be the same value just in 64 bit (instead of it representing a negative number which will what happen when sizeof(long) = 4). When -1023 <= (PVT_N_CONST * n - PVT_R_CONST) <= -1 dividing the number by 1024 should result of in 0, but because ">> 10" is used, and the sign bit is used to fill the vacated bit positions, it results in -1 (0xf...fffff) which is wrong. This change fixes the sign problem and supports negative values by casting n to long and replacing the shift right with div operation. Fixes: 9d823351a337 ("hwmon: Add hardware monitoring driver for Moortec MR75203 PVT controller") Signed-off-by: Eliav Farber <farbere@amazon.com> Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Link: https://lore.kernel.org/r/20220908152449.35457-5-farbere@amazon.com Signed-off-by: Guenter Roeck <linux@roeck-us.net>
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Tip revision: 227a3a2fc31d8e4bb9c88d4804e19530af245b1b authored by Eliav Farber on 08 September 2022, 15:24:32 UTC
hwmon: (mr75203) fix voltage equation for negative source input
hwmon: (mr75203) fix voltage equation for negative source input
Tip revision: 227a3a2
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