Re: [PATCH v2 7/7] iio: adc: ina2xx: Actually align the loop with the conversion ready flag

[Jonathan Cameron <jic23@kernel.org>]

On Thu, 21 Dec 2017 19:31:38 +0100
Stefan Brüns <stefan.bruens@rwth-aachen.de> wrote:

> Currently, the registers are read out once per conversion interval. If
> the reading is delayed as the conversion has not yet finished, this extra
> time is treated as being part of the readout, although it should delay
> the start of the poll interval. This results in the interval starting
> slightly earlier in each iteration, until all time between reads is
> spent polling the status registers instead of sleeping.
> 
> To fix this, the delay has to account for the state of the conversion
> ready flag. Whenever the conversion is already finished, schedule the next
> read on the regular interval, otherwise schedule it one interval after the
> flag bit has been set.
> 
> Split the work function in two functions, one for the status poll and one
> for reading the values, to be able to note down the time when the flag
> bit is raised.
> 
> Signed-off-by: Stefan Brüns <stefan.bruens@rwth-aachen.de>
Great thanks.

Applied to the togreg branch of iio.git and pushed out as testing
for the autobuilders to play with it.

Thanks,

Jonathan

> 
> ---
> 
> Changes in v2:
> - Describe old behaviour in commit message more clearly
> 
>  drivers/iio/adc/ina2xx-adc.c | 57 +++++++++++++++++++++++++++++---------------
>  1 file changed, 38 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/iio/adc/ina2xx-adc.c b/drivers/iio/adc/ina2xx-adc.c
> index b7407ac91b59..80af0d2322a3 100644
> --- a/drivers/iio/adc/ina2xx-adc.c
> +++ b/drivers/iio/adc/ina2xx-adc.c
> @@ -697,13 +697,10 @@ static const struct iio_chan_spec ina219_channels[] = {
>  	IIO_CHAN_SOFT_TIMESTAMP(4),
>  };
>  
> -static int ina2xx_work_buffer(struct iio_dev *indio_dev)
> +static int ina2xx_conversion_ready(struct iio_dev *indio_dev)
>  {
>  	struct ina2xx_chip_info *chip = iio_priv(indio_dev);
> -	/* data buffer needs space for channel data and timestap */
> -	unsigned short data[4 + sizeof(s64)/sizeof(short)];
> -	int bit, ret, i = 0;
> -	s64 time;
> +	int ret;
>  	unsigned int alert;
>  
>  	/*
> @@ -717,22 +714,29 @@ static int ina2xx_work_buffer(struct iio_dev *indio_dev)
>  	 * For now, we do an extra read of the MASK_ENABLE register (INA226)
>  	 * resp. the BUS_VOLTAGE register (INA219).
>  	 */
> -	if (!chip->allow_async_readout)
> -		do {
> -			if (chip->config->chip_id == ina226) {
> -				ret = regmap_read(chip->regmap,
> -						  INA226_MASK_ENABLE, &alert);
> -				alert &= INA226_CVRF;
> -			} else {
> -				ret = regmap_read(chip->regmap,
> -						  INA2XX_BUS_VOLTAGE, &alert);
> -				alert &= INA219_CNVR;
> -			}
> +	if (chip->config->chip_id == ina226) {
> +		ret = regmap_read(chip->regmap,
> +				  INA226_MASK_ENABLE, &alert);
> +		alert &= INA226_CVRF;
> +	} else {
> +		ret = regmap_read(chip->regmap,
> +				  INA2XX_BUS_VOLTAGE, &alert);
> +		alert &= INA219_CNVR;
> +	}
>  
> -			if (ret < 0)
> -				return ret;
> +	if (ret < 0)
> +		return ret;
>  
> -		} while (!alert);
> +	return !!alert;
> +}
> +
> +static int ina2xx_work_buffer(struct iio_dev *indio_dev)
> +{
> +	struct ina2xx_chip_info *chip = iio_priv(indio_dev);
> +	/* data buffer needs space for channel data and timestap */
> +	unsigned short data[4 + sizeof(s64)/sizeof(short)];
> +	int bit, ret, i = 0;
> +	s64 time;
>  
>  	time = iio_get_time_ns(indio_dev);
>  
> @@ -776,6 +780,21 @@ static int ina2xx_capture_thread(void *data)
>  	ktime_get_ts64(&next);
>  
>  	do {
> +		while (!chip->allow_async_readout) {
> +			ret = ina2xx_conversion_ready(indio_dev);
> +			if (ret < 0)
> +				return ret;
> +
> +			/*
> +			 * If the conversion was not yet finished,
> +			 * reset the reference timestamp.
> +			 */
> +			if (ret == 0)
> +				ktime_get_ts64(&next);
> +			else
> +				break;
> +		}
> +
>  		ret = ina2xx_work_buffer(indio_dev);
>  		if (ret < 0)
>  			return ret;