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

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Message-ID: <alpine.LRH.2.20.1611171613250.12237@pcbe13573-vm.dyndns.cern.ch>
Date:   Thu, 17 Nov 2016 17:23:53 +0100
From:   Tom Levens <tom.levens@...n.ch>
To:     Guenter Roeck <linux@...ck-us.net>
CC:     Tom Levens <tom.levens@...n.ch>, <jdelvare@...e.com>,
        <robh+dt@...nel.org>, <mark.rutland@....com>,
        <linux-kernel@...r.kernel.org>, <linux-hwmon@...r.kernel.org>,
        <devicetree@...r.kernel.org>
Subject: Re: [PATCH v2 1/3] hwmon: ltc2990: refactor value conversion

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@...n.ch>
>>  ---
>>   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@...n.ch>
>
> 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 @@
>>   #define LTC2990_CONTROL_MODE_CURRENT	0x06
>>   #define LTC2990_CONTROL_MODE_VOLTAGE	0x07
>>
>>  -/* 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.

> Thanks,
> Guenter

Cheers,