The patch titled
W1: w1_therm.c is flagging 0C etc as invalid
has been added to the -mm tree. Its filename is
w1-w1_thermc-is-flagging-0c-etc-as-invalid.patch
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The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: W1: w1_therm.c is flagging 0C etc as invalid
From: David Fries <david@xxxxxxxxx>
The extra rom[0] check is flagging valid temperatures as invalid when
there is already a CRC data transmission check.
w1_therm_read_bin()
if (rom[8] == crc && rom[0])
verdict = 1;
Requiring rom[0] to be non-zero will flag as invalid temperature
conversions when the low byte is zero, specifically the temperatures 0C,
16C, 32C, 48C, -16C, -32C, and -48C.
The CRC check is produced on the device for the previous 8 bytes and is
required to ensure the data integrity in transmission. I don't see why the
extra check for rom[0] being non-zero is in there. Evgeniy Polyakov didn't
know either. Just for a check I unplugged the sensor, executed a
temperature conversion, and read the results. The read was all ff's, which
also failed the CRC, so it doesn't need to protect against a disconnected
sensor.
I have more extensive patches in the work, but these two trivial ones will
do for today. I would like to hear from people who use the ds2490 USB to
one wire dongle. 1 if you would be willing to test the patches as I
currently only have the one sensor on a short parisite powered wire, 2 if
there is any cheap sources for the ds2490.
Signed-off-by: David Fries <david@xxxxxxxxx>
Acked-by: Evgeniy Polyakov <johnpol@xxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
drivers/w1/slaves/w1_therm.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff -puN drivers/w1/slaves/w1_therm.c~w1-w1_thermc-is-flagging-0c-etc-as-invalid drivers/w1/slaves/w1_therm.c
--- a/drivers/w1/slaves/w1_therm.c~w1-w1_thermc-is-flagging-0c-etc-as-invalid
+++ a/drivers/w1/slaves/w1_therm.c
@@ -204,7 +204,7 @@ static ssize_t w1_therm_read_bin(struct
crc = w1_calc_crc8(rom, 8);
- if (rom[8] == crc && rom[0])
+ if (rom[8] == crc)
verdict = 1;
}
}
_
Patches currently in -mm which might be from david@xxxxxxxxx are
w1-w1_thermc-ds18b20-decode-freezing-temperatures-correctly.patch
w1-w1_thermc-is-flagging-0c-etc-as-invalid.patch
system-timer-fix-crash-in-100hz-system-timer.patch
system-timer-fix-crash-in-100hz-system-timer-cleanup.patch
speed-up-jiffies-conversion-functions-if-hz==user_hz.patch
-
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