linux-kernel - [009/117] w1: w1 temp: fix negative termperature calculation

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Date:	Mon, 10 May 2010 15:31:40 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Evgeniy Polyakov <johnpol@....mipt.ru>
Subject: [009/117] w1: w1 temp: fix negative termperature calculation

2.6.33-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Ian Dall <ian@...are.dropbear.id.au>

commit 9a6a1ecd9e9b5d046a236da2f7eb6b6812f04229 upstream.

Fix regression caused by commit 507e2fbaaacb6f164b4125b87c5002f95143174b
("w1: w1 temp calculation overflow fix") whereby negative temperatures for
the DS18B20 are not converted properly.

When the temperature exceeds 32767 milli-degrees the temperature overflows
to -32768 millidegrees.  These are both well within the -55 - +125 degree
range for the sensor.

Addresses https://bugzilla.kernel.org/show_bug.cgi?id=12646

Signed-of-by: Ian Dall <ian@...are.dropbear.id.au>
Cc: Evgeniy Polyakov <johnpol@....mipt.ru>
Tested-by: Karsten Elfenbein <kelfe@....de>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 drivers/w1/slaves/w1_therm.c |    5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

--- a/drivers/w1/slaves/w1_therm.c
+++ b/drivers/w1/slaves/w1_therm.c
@@ -115,9 +115,8 @@ static struct w1_therm_family_converter
 
 static inline int w1_DS18B20_convert_temp(u8 rom[9])
 {
-	int t = ((s16)rom[1] << 8) | rom[0];
-	t = t*1000/16;
-	return t;
+	s16 t = le16_to_cpup((__le16 *)rom);
+	return t*1000/16;
 }
 
 static inline int w1_DS18S20_convert_temp(u8 rom[9])


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