linux-kernel - [099/197] hwmon: (sht15) Fix sht15_calc

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Date:	Thu, 22 Apr 2010 12:09:10 -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,
	Jerome Oufella <jerome.oufella@...oirfairelinux.com>,
	Jonathan Cameron <jic23@....ac.uk>,
	Jean Delvare <khali@...ux-fr.org>
Subject: [099/197] hwmon: (sht15) Fix sht15_calc_temp interpolation function

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

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

From: Jerome Oufella <jerome.oufella@...oirfairelinux.com>

commit 328a2c22abd08911e37fa66f1358f829cecd72e9 upstream.

I discovered two issues.
First the previous sht15_calc_temp() loop did not iterate through the
temppoints array since the (data->supply_uV > temppoints[i - 1].vdd)
test is always true in this direction.

Also the two-points linear interpolation function was returning biased
values due to a stray division by 1000 which shouldn't be there.

[JD: Also change the default value for d1 from 0 to something saner.]

Signed-off-by: Jerome Oufella <jerome.oufella@...oirfairelinux.com>
Acked-by: Jonathan Cameron <jic23@....ac.uk>
Signed-off-by: Jean Delvare <khali@...ux-fr.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 drivers/hwmon/sht15.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/drivers/hwmon/sht15.c
+++ b/drivers/hwmon/sht15.c
@@ -302,13 +302,13 @@ error_ret:
  **/
 static inline int sht15_calc_temp(struct sht15_data *data)
 {
-	int d1 = 0;
+	int d1 = temppoints[0].d1;
 	int i;
 
-	for (i = 1; i < ARRAY_SIZE(temppoints); i++)
+	for (i = ARRAY_SIZE(temppoints) - 1; i > 0; i--)
 		/* Find pointer to interpolate */
 		if (data->supply_uV > temppoints[i - 1].vdd) {
-			d1 = (data->supply_uV/1000 - temppoints[i - 1].vdd)
+			d1 = (data->supply_uV - temppoints[i - 1].vdd)
 				* (temppoints[i].d1 - temppoints[i - 1].d1)
 				/ (temppoints[i].vdd - temppoints[i - 1].vdd)
 				+ temppoints[i - 1].d1;


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