linux-kernel - [PATCH] power: max8925_power: Fix incorrect voltage and current calculation

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Date:	Fri, 26 Aug 2011 13:28:22 -0700
From:	Philip Rakity <prakity@...vell.com>
To:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Haojian Zhuang <haojian.zhuang@...il.com>
Subject: [PATCH] power: max8925_power: Fix incorrect voltage and current
  calculation


The datasheet indicates a 12 bit value is returned for i2c
registers for voltage and current.  Code was assuming 8 bits.
But default for chip is 12 bit return value.

Voltage is returned in 2mV units  -- adjust to return as uV
per linux power spec

Adjust current calculation to return units in uA
*** NOT POSSIBLE TO VALIDATE THIS since my h/w does not have
current hooked up to 8925 *****

Signed-off-by: Philip Rakity <prakity@...vell.com>
---
 drivers/power/max8925_power.c |   13 ++++++-------
 1 files changed, 6 insertions(+), 7 deletions(-)

diff --git a/drivers/power/max8925_power.c b/drivers/power/max8925_power.c
index 29b5d2c..5e4e046 100644
--- a/drivers/power/max8925_power.c
+++ b/drivers/power/max8925_power.c
@@ -190,7 +190,7 @@ static int start_measure(struct max8925_power_info *info, int type)
 	}
 
 	max8925_bulk_read(info->adc, meas_reg, 2, buf);
-	ret = (buf[0] << 4) | (buf[1] >> 4);
+	ret = ((buf[0]<<8) | buf[1]) >> 4;
 
 	return ret;
 }
@@ -210,7 +210,7 @@ static int max8925_ac_get_prop(struct power_supply *psy,
 		if (info->ac_online) {
 			ret = start_measure(info, MEASURE_VCHG);
 			if (ret >= 0) {
-				val->intval = ret << 1;	/* unit is mV */
+				val->intval = ret * 2000;	/* unit is uV */
 				goto out;
 			}
 		}
@@ -244,7 +244,7 @@ static int max8925_usb_get_prop(struct power_supply *psy,
 		if (info->usb_online) {
 			ret = start_measure(info, MEASURE_VCHG);
 			if (ret >= 0) {
-				val->intval = ret << 1;	/* unit is mV */
+				val->intval = ret * 2000;	/* unit is uV */
 				goto out;
 			}
 		}
@@ -268,7 +268,6 @@ static int max8925_bat_get_prop(struct power_supply *psy,
 				union power_supply_propval *val)
 {
 	struct max8925_power_info *info = dev_get_drvdata(psy->dev->parent);
-	long long int tmp = 0;
 	int ret = 0;
 
 	switch (psp) {
@@ -279,7 +278,7 @@ static int max8925_bat_get_prop(struct power_supply *psy,
 		if (info->bat_online) {
 			ret = start_measure(info, MEASURE_VMBATT);
 			if (ret >= 0) {
-				val->intval = ret << 1;	/* unit is mV */
+				val->intval = ret * 2000;	/* unit is uV */
 				ret = 0;
 				break;
 			}
@@ -290,8 +289,8 @@ static int max8925_bat_get_prop(struct power_supply *psy,
 		if (info->bat_online) {
 			ret = start_measure(info, MEASURE_ISNS);
 			if (ret >= 0) {
-				tmp = (long long int)ret * 6250 / 4096 - 3125;
-				ret = (int)tmp;
+				/* assume r_sns is 0.02 */
+				ret = ((ret * 6250) - 3125) /* uA */;
 				val->intval = 0;
 				if (ret > 0)
 					val->intval = ret; /* unit is mA */
-- 
1.7.6

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