linux-kernel - [PATCHv2] hwmon: adm9240: handle temperature readings below 0

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Message-Id: <20161004214054.18501-1-chris.packham@alliedtelesis.co.nz>
Date:   Wed,  5 Oct 2016 10:40:54 +1300
From:   Chris Packham <chris.packham@...iedtelesis.co.nz>
To:     jdelvare@...e.com, linux@...ck-us.net, linux-hwmon@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     Michael.Wang@...iedtelesis.co.nz,
        Chris Packham <chris.packham@...iedtelesis.co.nz>
Subject: [PATCHv2] hwmon: adm9240: handle temperature readings below 0

Unlike the temperature thresholds the temperature data is a 9-bit signed
value. This allows and additional 0.5 degrees of precision on the
reading but makes handling negative values slightly harder. In order to
have sign-extension applied correctly the 9-bit value is stored in the
upper bits of a signed 16-bit value. When presenting this in sysfs the
value is shifted and scaled appropriately.

Signed-off-by: Chris Packham <chris.packham@...iedtelesis.co.nz>
---
Changes in v2:
- Simplify as per feedback from Guenter.
- Re-word commit message.

 drivers/hwmon/adm9240.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/hwmon/adm9240.c b/drivers/hwmon/adm9240.c
index 98114ce..8d8ede8 100644
--- a/drivers/hwmon/adm9240.c
+++ b/drivers/hwmon/adm9240.c
@@ -197,7 +197,7 @@ static struct adm9240_data *adm9240_update_device(struct device *dev)
 		data->temp = ((i2c_smbus_read_byte_data(client,
 					ADM9240_REG_TEMP) << 8) |
 					i2c_smbus_read_byte_data(client,
-					ADM9240_REG_TEMP_CONF)) / 128;
+					ADM9240_REG_TEMP_CONF));
 
 		for (i = 0; i < 2; i++) { /* read fans */
 			data->fan[i] = i2c_smbus_read_byte_data(client,
@@ -263,7 +263,7 @@ static ssize_t show_temp(struct device *dev, struct device_attribute *dummy,
 		char *buf)
 {
 	struct adm9240_data *data = adm9240_update_device(dev);
-	return sprintf(buf, "%d\n", data->temp * 500); /* 9-bit value */
+	return sprintf(buf, "%d\n", data->temp / 128 * 500); /* 9-bit value */
 }
 
 static ssize_t show_max(struct device *dev, struct device_attribute *devattr,
-- 
2.10.1