From: Ivan Zaentsev ivan.zaentsev@wirenboard.ru
commit 2f6055c26f1913763eabc66c7c27d0693561e966 upstream.
DS18B20 device driver returns an incorrect value for negative temperatures due to a missing sign-extension in w1_DS18B20_convert_temp().
Fix by using s16 temperature value when converting to int.
Fixes: 9ace0b4dab1c (w1: w1_therm: Add support for GXCAS GX20MH01 device.) Cc: stable stable@vger.kernel.org Reported-by: Paweł Marciniak sunwire@gmail.com Signed-off-by: Ivan Zaentsev ivan.zaentsev@wirenboard.ru Link: https://lore.kernel.org/r/20210121093021.224764-1-ivan.zaentsev@wirenboard.r... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/w1/slaves/w1_therm.c | 22 +++++++++------------- 1 file changed, 9 insertions(+), 13 deletions(-)
--- a/drivers/w1/slaves/w1_therm.c +++ b/drivers/w1/slaves/w1_therm.c @@ -667,28 +667,24 @@ static inline int w1_DS18B20_get_resolut */ static inline int w1_DS18B20_convert_temp(u8 rom[9]) { - int t; - u32 bv; + u16 bv; + s16 t; + + /* Signed 16-bit value to unsigned, cpu order */ + bv = le16_to_cpup((__le16 *)rom);
/* Config register bit R2 = 1 - GX20MH01 in 13 or 14 bit resolution mode */ if (rom[4] & 0x80) { - /* Signed 16-bit value to unsigned, cpu order */ - bv = le16_to_cpup((__le16 *)rom); - /* Insert two temperature bits from config register */ /* Avoid arithmetic shift of signed value */ bv = (bv << 2) | (rom[4] & 3); - - t = (int) sign_extend32(bv, 17); /* Degrees, lowest bit is 2^-6 */ - return (t*1000)/64; /* Millidegrees */ + t = (s16) bv; /* Degrees, lowest bit is 2^-6 */ + return (int)t * 1000 / 64; /* Sign-extend to int; millidegrees */ } - - t = (int)le16_to_cpup((__le16 *)rom); - return t*1000/16; + t = (s16)bv; /* Degrees, lowest bit is 2^-4 */ + return (int)t * 1000 / 16; /* Sign-extend to int; millidegrees */ }
- - /** * w1_DS18S20_convert_temp() - temperature computation for DS18S20 * @rom: data read from device RAM (8 data bytes + 1 CRC byte)