Re: [PATCH] hwmon: (ina3221) Add voltage conversion time settings

[Guenter Roeck <linux@roeck-us.net>]

On 4/17/19 6:46 AM, Guenter Roeck wrote:
> On 4/16/19 4:55 PM, Nicolin Chen wrote:
>> The CONFIG register has two 3-bit fields for conversion time
>> settings of Bus-voltage and Shunt-voltage, respectively. The
>> conversion settings, along with averaging mode, allow users
>> to optimize available timing requirement.
>>
>> This patch adds an 'update_interval' sysfs node through the
>> hwmon_chip_info of hwmon core. It reflects a total hardware
>> conversion time:
>>      samples * channels * (Bus + Shunt conversion times)
>>
>> Though INA3221 supports different conversion time setups for
>> Bus and Shunt voltages, this patch only adds the support of
>> a unified setting for both conversion times, by dividing the
>> conversion time into two equal values.
>>
>> Signed-off-by: Nicolin Chen <nicoleotsuka@gmail.com>
>> ---
>>
>> Hi Guenter,
>>
>> I am not quite sure if this update_interval is the best way to
>> implement the conversion time settings but I can't find another
>> common approach. This implementation certainly has drawbacks:
>>   1) It can't configure Bus and Shunt conversion times separately
>>      (Not crucial for me at this point as I set them equally)
>>   2) Users need to calculate for the settings of conversion time
>>   3) The ABI defines update_interval in msec while the hardware
>>      and datasheet does in usec, and that generates rounding diff
>>   4) The update_interval value would be spontaneously modified
>>      everytime number of samples or number of enabled channels
>>      gets changed. This might confuses users who tries to have
>>      a fixed update_interval other than really merely setting
>>      conversion time.
>>
>> I see IIO subsystem have something like IIO_CHAN_INFO_INT_TIME
>> for conversion time setting exclusively. Do we have something
>> similar under hwmon?
>>
> 
> No. I think what you have should be good enough for now.
> Please see comments below.
> 
> Thanks,
> Guenter
> 
>> Thanks
>>
>>   Documentation/hwmon/ina3221 |  9 +++++
>>   drivers/hwmon/ina3221.c     | 65 ++++++++++++++++++++++++++++++++-----
>>   2 files changed, 65 insertions(+), 9 deletions(-)
>>
>> diff --git a/Documentation/hwmon/ina3221 b/Documentation/hwmon/ina3221
>> index ed3f22769d4b..3b05170112f0 100644
>> --- a/Documentation/hwmon/ina3221
>> +++ b/Documentation/hwmon/ina3221
>> @@ -38,3 +38,12 @@ in[456]_input           Shunt voltage(uV) for channels 1, 2, and 3 respectively
>>   samples                 Number of samples using in the averaging mode.
>>                             Supports the list of number of samples:
>>                             1, 4, 16, 64, 128, 256, 512, 1024
>> +update_interval         Data conversion time in millisecond, following:
>> +                          update_interval = C x S x (BC + SC)
>> +                              C: number of enabled channels
>> +                              S: number of samples
>> +                             BC: bus-voltage conversion time in millisecond
>> +                             SC: shunt-voltage conversion time in millisecond
>> +                          Affects both Bus- and Shunt-voltage conversion time.
>> +                          Note that setting update_interval to 0ms sets both BC
>> +                          and SC to 140 us (minimum conversion time).
>> diff --git a/drivers/hwmon/ina3221.c b/drivers/hwmon/ina3221.c
>> index 74d39d212931..af4ab8ddddce 100644
>> --- a/drivers/hwmon/ina3221.c
>> +++ b/drivers/hwmon/ina3221.c
>> @@ -144,19 +144,37 @@ static const int ina3221_avg_samples[] = {
>>       1, 4, 16, 64, 128, 256, 512, 1024,
>>   };
>> -static inline int ina3221_wait_for_data(struct ina3221_data *ina)
>> +/* Converting update_interval in msec to conversion time in usec */
>> +static inline u32 ina3221_interval_ms_to_conv_time(u16 config, int interval)
>>   {
>> -    u32 channels = hweight16(ina->reg_config & INA3221_CONFIG_CHs_EN_MASK);
>> -    u32 vbus_ct_idx = INA3221_CONFIG_VBUS_CT(ina->reg_config);
>> -    u32 vsh_ct_idx = INA3221_CONFIG_VSH_CT(ina->reg_config);
>> -    u32 samples_idx = INA3221_CONFIG_AVG(ina->reg_config);
>> +    u32 channels = hweight16(config & INA3221_CONFIG_CHs_EN_MASK);
>> +    u32 samples_idx = INA3221_CONFIG_AVG(config);
>> +    u32 samples = ina3221_avg_samples[samples_idx];
>> +
>> +    /* Bisect the result to Bus and Shunt conversion times */
>> +    return DIV_ROUND_CLOSEST(interval * 1000 / 2, channels * samples);
>> +}
>> +
>> +/* Converting CONFIG register value to update_interval in usec */
>> +static inline u32 ina3221_reg_to_interval_us(u16 config)
>> +{
>> +    u32 channels = hweight16(config & INA3221_CONFIG_CHs_EN_MASK);
>> +    u32 vbus_ct_idx = INA3221_CONFIG_VBUS_CT(config);
>> +    u32 vsh_ct_idx = INA3221_CONFIG_VSH_CT(config);
>> +    u32 samples_idx = INA3221_CONFIG_AVG(config);
>>       u32 samples = ina3221_avg_samples[samples_idx];
>>       u32 vbus_ct = ina3221_conv_time[vbus_ct_idx];
>>       u32 vsh_ct = ina3221_conv_time[vsh_ct_idx];
>> -    u32 wait, cvrf;
>>       /* Calculate total conversion time */
>> -    wait = channels * (vbus_ct + vsh_ct) * samples;
>> +    return channels * (vbus_ct + vsh_ct) * samples;
>> +}
>> +
>> +static inline int ina3221_wait_for_data(struct ina3221_data *ina)
>> +{
>> +    u32 wait, cvrf;
>> +
>> +    wait = ina3221_reg_to_interval_us(ina->reg_config);
>>       /* Polling the CVRF bit to make sure read data is ready */
>>       return regmap_field_read_poll_timeout(ina->fields[F_CVRF],
>> @@ -197,6 +215,11 @@ static int ina3221_read_chip(struct device *dev, u32 attr, long *val)
>>           regval = INA3221_CONFIG_AVG(ina->reg_config);
>>           *val = ina3221_avg_samples[regval];
>>           return 0;
>> +    case hwmon_chip_update_interval:
>> +        /* Return in msec */
>> +        *val = ina3221_reg_to_interval_us(ina->reg_config);
>> +        *val = DIV_ROUND_CLOSEST(*val, 1000);
>> +        return 0;
>>       default:
>>           return -EOPNOTSUPP;
>>       }
>> @@ -308,7 +331,7 @@ static int ina3221_read_curr(struct device *dev, u32 attr,
>>   static int ina3221_write_chip(struct device *dev, u32 attr, long val)
>>   {
>>       struct ina3221_data *ina = dev_get_drvdata(dev);
>> -    int ret, idx;
>> +    int ret, idx, tmp;
>>       switch (attr) {
>>       case hwmon_chip_samples:
>> @@ -321,6 +344,28 @@ static int ina3221_write_chip(struct device *dev, u32 attr, long val)
>>           if (ret)
>>               return ret;
>> +        /* Update reg_config accordingly */
>> +        return regmap_read(ina->regmap, INA3221_CONFIG,
>> +                   &ina->reg_config);
>> +    case hwmon_chip_update_interval:
>> +        tmp = ina3221_interval_ms_to_conv_time(ina->reg_config, val);
>> +        idx = find_closest(tmp, ina3221_conv_time,
>> +                   ARRAY_SIZE(ina3221_conv_time));
>> +
>> +        /* Update Bus-voltage conversion time */
>> +        ret = regmap_update_bits(ina->regmap, INA3221_CONFIG,
>> +                     INA3221_CONFIG_VBUS_CT_MASK,
>> +                     idx << INA3221_CONFIG_VBUS_CT_SHIFT);
>> +        if (ret)
>> +            return ret;
>> +
>> +        /* Update Shunt-voltage conversion time */
>> +        ret = regmap_update_bits(ina->regmap, INA3221_CONFIG,
>> +                     INA3221_CONFIG_VSH_CT_MASK,
>> +                     idx << INA3221_CONFIG_VSH_CT_SHIFT);
>> +        if (ret)
>> +            return ret;
> 
> It should be possible to update both conversion times with a single call,
> since both calls touch only one register. Something like
> 
>          ret = regmap_update_bits(ina->regmap, INA3221_CONFIG
>              INA3221_CONFIG_VBUS_CT_MASK | INA3221_CONFIG_VSH_CT_MASK,
>              (idx << INA3221_CONFIG_VBUS_CT_SHIFT) | (idx << INA3221_CONFIG_VSH_CT_SHIFT));
> 
> Granted, that is a bit long, but it saves an extra i2c write operation.
> 

Thinking about it ... does it even make sense to cache reg_config twice,
or would it be better to just update the local copy and use regmap_write()
to send it to the chip ?

Guenter

>> +
>>           /* Update reg_config accordingly */
>>           return regmap_read(ina->regmap, INA3221_CONFIG,
>>                      &ina->reg_config);
>> @@ -482,6 +527,7 @@ static umode_t ina3221_is_visible(const void *drvdata,
>>       case hwmon_chip:
>>           switch (attr) {
>>           case hwmon_chip_samples:
>> +        case hwmon_chip_update_interval:
>>               return 0644;
>>           default:
>>               return 0;
>> @@ -527,7 +573,8 @@ static umode_t ina3221_is_visible(const void *drvdata,
>>   static const struct hwmon_channel_info *ina3221_info[] = {
>>       HWMON_CHANNEL_INFO(chip,
>> -               HWMON_C_SAMPLES),
>> +               HWMON_C_SAMPLES,
>> +               HWMON_C_UPDATE_INTERVAL),
>>       HWMON_CHANNEL_INFO(in,
>>                  /* 0: dummy, skipped in is_visible */
>>                  HWMON_I_INPUT,
>>
> 
>