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

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Date:   Thu, 17 Nov 2016 08:36:07 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Tom Levens <tom.levens@...n.ch>
Cc:     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

On 11/17/2016 08:23 AM, Tom Levens wrote:
> 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.
>
Ah, ok. Good to know. Please leave it anyway, reason being that there is no real
reason to change it. Effectively those are just whitespace changes (unlike the rest,
which is part bug fix, part cleanup).

>> Can you send me a register map for the chip ? I would like to write a module test.
>
> Here is an example register dump:

I meant the output of i2cdump (something like "i2cdump -y -f <bus> <i2c-address> w").

Thanks,
Guenter

>
> 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,
>