This is a note to let you know that I've just added the patch titled
w1: w1_therm: Fix conversion result for negative temperatures
to my char-misc git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git
in the char-misc-testing branch.
The patch will show up in the next release of the linux-next tree
(usually sometime within the next 24 hours during the week.)
The patch will be merged to the char-misc-next branch sometime soon,
after it passes testing, and the merge window is open.
If you have any questions about this process, please let me know.
>From 2f6055c26f1913763eabc66c7c27d0693561e966 Mon Sep 17 00:00:00 2001
From: Ivan Zaentsev <ivan.zaentsev@xxxxxxxxxxxxx>
Date: Thu, 21 Jan 2021 12:30:21 +0300
Subject: w1: w1_therm: Fix conversion result for negative temperatures
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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@xxxxxxxxxxxxxxx>
Reported-by: Paweł Marciniak <sunwire@xxxxxxxxx>
Signed-off-by: Ivan Zaentsev <ivan.zaentsev@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20210121093021.224764-1-ivan.zaentsev@xxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/w1/slaves/w1_therm.c | 22 +++++++++-------------
1 file changed, 9 insertions(+), 13 deletions(-)
diff --git a/drivers/w1/slaves/w1_therm.c b/drivers/w1/slaves/w1_therm.c
index 3712b1e6dc71..976eea28f268 100644
--- a/drivers/w1/slaves/w1_therm.c
+++ b/drivers/w1/slaves/w1_therm.c
@@ -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)
--
2.30.0
