linux-kernel - [PATCH] hwmon: (pmbus) Use 64bit math for DIRECT format values

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Message-Id: <20171122220843.18309-1-rlippert@google.com>
Date:   Wed, 22 Nov 2017 14:08:43 -0800
From:   Robert Lippert <roblip@...il.com>
To:     linux@...ck-us.net
Cc:     linux-hwmon@...r.kernel.org, jdelvare@...e.com,
        linux-kernel@...r.kernel.org, xow@...gle.com,
        Robert Lippert <rlippert@...gle.com>
Subject: [PATCH] hwmon: (pmbus) Use 64bit math for DIRECT format values

Power values in the 100s of watt range can easily blow past
32bit math limits when processing everything in microwatts.

Use 64bit math instead to avoid these issues on common 32bit ARM
BMC platforms.

Signed-off-by: Robert Lippert <rlippert@...gle.com>
---
 drivers/hwmon/pmbus/pmbus_core.c | 21 ++++++++++++---------
 1 file changed, 12 insertions(+), 9 deletions(-)

diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c
index 52a58b8b6e1b..f4efea9f282e 100644
--- a/drivers/hwmon/pmbus/pmbus_core.c
+++ b/drivers/hwmon/pmbus/pmbus_core.c
@@ -499,8 +499,8 @@ static long pmbus_reg2data_linear(struct pmbus_data *data,
 static long pmbus_reg2data_direct(struct pmbus_data *data,
 				  struct pmbus_sensor *sensor)
 {
-	long val = (s16) sensor->data;
-	long m, b, R;
+	s64 val = (s16) sensor->data;
+	s64 m, b, R;
 
 	m = data->info->m[sensor->class];
 	b = data->info->b[sensor->class];
@@ -528,11 +528,13 @@ static long pmbus_reg2data_direct(struct pmbus_data *data,
 		R--;
 	}
 	while (R < 0) {
-		val = DIV_ROUND_CLOSEST(val, 10);
+		do_div(val, 10);
 		R++;
 	}
 
-	return (val - b) / m;
+	val = val - b;
+	do_div(val, m);
+	return val;
 }
 
 /*
@@ -656,7 +658,8 @@ static u16 pmbus_data2reg_linear(struct pmbus_data *data,
 static u16 pmbus_data2reg_direct(struct pmbus_data *data,
 				 struct pmbus_sensor *sensor, long val)
 {
-	long m, b, R;
+	s64 m, b, R;
+	s64 val64 = val;
 
 	m = data->info->m[sensor->class];
 	b = data->info->b[sensor->class];
@@ -673,18 +676,18 @@ static u16 pmbus_data2reg_direct(struct pmbus_data *data,
 		R -= 3;		/* Adjust R and b for data in milli-units */
 		b *= 1000;
 	}
-	val = val * m + b;
+	val64 = val64 * m + b;
 
 	while (R > 0) {
-		val *= 10;
+		val64 *= 10;
 		R--;
 	}
 	while (R < 0) {
-		val = DIV_ROUND_CLOSEST(val, 10);
+		do_div(val64, 10);
 		R++;
 	}
 
-	return val;
+	return (u16) val64;
 }
 
 static u16 pmbus_data2reg_vid(struct pmbus_data *data,
-- 
2.15.0.448.gf294e3d99a-goog