Re: [PATCH v2 1/3] hwmon: ltc2990: refactor value conversion

From: Tom Levens
Date: Thu Nov 17 2016 - 12:13:54 EST

Hi Guenter,

Thanks for taking the time to review the patch.

On Thu, 17 Nov 2016, Guenter Roeck wrote:

Hi Tom,

On 11/17/2016 04:10 AM, Tom Levens wrote:
Conversion from raw values to signed integers has been refactored using
the macros in bitops.h.

Please also mention that this fixes a bug in negative temperature conversions.

Yes, of course, I will include the information in v3.

Signed-off-by: Tom Levens <tom.levens@xxxxxxx>
drivers/hwmon/ltc2990.c | 27 ++++++++++-----------------
1 files changed, 10 insertions(+), 17 deletions(-)

diff --git a/drivers/hwmon/ltc2990.c b/drivers/hwmon/ltc2990.c
index 8f8fe05..0ec4102 100644
--- a/drivers/hwmon/ltc2990.c
+++ b/drivers/hwmon/ltc2990.c
@@ -9,8 +9,12 @@
* This driver assumes the chip is wired as a dual current monitor, and
* reports the voltage drop across two series resistors. It also reports
* the chip's internal temperature and Vcc power supply voltage.
+ *
+ * Value conversion refactored
+ * by Tom Levens <tom.levens@xxxxxxx>

Kind of unusual to do that for minor changes like this. Imagine if everyone would do that.
The commit log is what gives you credit.

Good point, thanks for the hint. I will remove it from v3.


+#include <linux/bitops.h>
#include <linux/err.h>
#include <linux/hwmon.h>
#include <linux/hwmon-sysfs.h>
@@ -34,19 +38,10 @@

-/* convert raw register value to sign-extended integer in 16-bit range */
-static int ltc2990_voltage_to_int(int raw)
- if (raw & BIT(14))
- return -(0x4000 - (raw & 0x3FFF)) << 2;
- else
- return (raw & 0x3FFF) << 2;
/* Return the converted value from the given register in uV or mC */
-static int ltc2990_get_value(struct i2c_client *i2c, u8 reg, int *result)
+static int ltc2990_get_value(struct i2c_client *i2c, u8 reg, s32 *result)
- int val;
+ s32 val;

Please just leave the variable type alone. it is also used for the return value
from i2c_smbus_read_word_swapped(), which is an int, and changing it to s32 doesn't really make the code better.

According to i2c.h the return type for i2c_smbus_read_word_swapped() is s32, which is why I modified it here. But it could be changed back if you think it is better to leave it as an int.

Can you send me a register map for the chip ? I would like to write a module test.

Here is an example register dump:

00 00 00 00
01 90 07 d0
2c cd 7d 80
7c 29 20 00

The expected values in this case are:

in0_input 5000
in1_input 610
in2_input 3500
in3_input -195
in4_input -299
temp1_input 25000
temp2_input 125000
temp3_input -40000
curr1_input 38840
curr2_input -12428

Testing with lltc,mode set to <5>, <6> and <7> should give you all measurements.