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w1: w1_therm: Fix conversion result for negative temperatures 

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: 9ace0b4dab (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.ru
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Ivan Zaentsev 2021-01-21 12:30:21 +03:00 committed by Greg Kroah-Hartman
parent 2c104a469a
commit 2f6055c26f
1 changed files with 9 additions and 13 deletions
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22
drivers/w1/slaves/w1_therm.c
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@ -667,28 +667,24 @@ static inline int w1_DS18B20_get_resolution(struct w1_slave *sl)
*/
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)