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

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

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.

> +
>   		/* 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,
>