Re: [v2 5/8] iio: adc: aspeed: Add func to set sampling rate.

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

On Fri, 23 Jul 2021 16:16:18 +0800
Billy Tsai <billy_tsai@aspeedtech.com> wrote:

> Add the function to set the sampling rate and keep the sampling period
> for a driver used to wait the lastest value.
> 
> Signed-off-by: Billy Tsai <billy_tsai@aspeedtech.com>
A few follow on comments from suggestion in early patch, but otherwise this
looks good to me.

Jonathan

> ---
>  drivers/iio/adc/aspeed_adc.c | 48 +++++++++++++++++++++++++-----------
>  1 file changed, 33 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/iio/adc/aspeed_adc.c b/drivers/iio/adc/aspeed_adc.c
> index 84f079195375..bb6100228cae 100644
> --- a/drivers/iio/adc/aspeed_adc.c
> +++ b/drivers/iio/adc/aspeed_adc.c
> @@ -55,6 +55,12 @@
>  
>  #define ASPEED_ADC_INIT_POLLING_TIME	500
>  #define ASPEED_ADC_INIT_TIMEOUT		500000
> +/*
> + * When the sampling rate is too high, the ADC may not have enough charging
> + * time, resulting in a low voltage value. Thus, default use slow sampling
> + * rate for most user case.
> + */
> +#define ASPEED_ADC_DEF_SAMPLING_RATE	65000
>  
>  enum aspeed_adc_version {
>  	aspeed_adc_ast2400,
> @@ -77,6 +83,7 @@ struct aspeed_adc_data {
>  	struct clk_hw		*clk_scaler;
>  	struct reset_control	*rst;
>  	int			vref;
> +	u32			sample_period_ns;
>  };
>  
>  #define ASPEED_CHAN(_idx, _data_reg_addr) {			\
> @@ -108,6 +115,26 @@ static const struct iio_chan_spec aspeed_adc_iio_channels[] = {
>  	ASPEED_CHAN(15, 0x2E),
>  };
>  
> +static int aspeed_adc_set_sampling_rate(struct iio_dev *indio_dev, u32 rate)
> +{
> +	struct aspeed_adc_data *data = iio_priv(indio_dev);
> +	const struct aspeed_adc_model_data *model_data =
> +		of_device_get_match_data(data->dev);

As in previous patch, this would be cleaner if there was a cached copy of
the model_data pointer in data rather than looking it up each time.

> +
> +	if (rate < model_data->min_sampling_rate ||
> +	    rate > model_data->max_sampling_rate)
> +		return -EINVAL;
> +	/* Each sampling needs 12 clocks to covert.*/
> +	clk_set_rate(data->clk_scaler->clk, rate * ASPEED_CLOCKS_PER_SAMPLE);
> +
> +	rate = clk_get_rate(data->clk_scaler->clk);
> +	data->sample_period_ns = DIV_ROUND_UP_ULL(
> +		(u64)NSEC_PER_SEC * ASPEED_CLOCKS_PER_SAMPLE, rate);
> +	dev_dbg(data->dev, "Adc clock = %d sample period = %d ns", rate,
> +		data->sample_period_ns);

blank line here.

> +	return 0;
> +}
> +
>  static int aspeed_adc_read_raw(struct iio_dev *indio_dev,
>  			       struct iio_chan_spec const *chan,
>  			       int *val, int *val2, long mask)
> @@ -138,19 +165,9 @@ static int aspeed_adc_write_raw(struct iio_dev *indio_dev,
>  				struct iio_chan_spec const *chan,
>  				int val, int val2, long mask)
>  {
> -	struct aspeed_adc_data *data = iio_priv(indio_dev);
> -	const struct aspeed_adc_model_data *model_data =
> -			of_device_get_match_data(data->dev);
> -
>  	switch (mask) {
>  	case IIO_CHAN_INFO_SAMP_FREQ:
> -		if (val < model_data->min_sampling_rate ||
> -			val > model_data->max_sampling_rate)
> -			return -EINVAL;
> -
> -		clk_set_rate(data->clk_scaler->clk,
> -				val * ASPEED_CLOCKS_PER_SAMPLE);
> -		return 0;
> +		return aspeed_adc_set_sampling_rate(indio_dev, val);
>  
>  	case IIO_CHAN_INFO_SCALE:
>  	case IIO_CHAN_INFO_RAW:
> @@ -302,6 +319,10 @@ static int aspeed_adc_probe(struct platform_device *pdev)
>  		goto reset_error;
>  	}
>  	reset_control_deassert(data->rst);
> +	ret = clk_prepare_enable(data->clk_scaler->clk);
> +	if (ret)
> +		goto clk_enable_error;
> +	aspeed_adc_set_sampling_rate(indio_dev, ASPEED_ADC_DEF_SAMPLING_RATE);
>  
>  	ret = aspeed_adc_vref_config(pdev);
>  	if (ret)
> @@ -327,9 +348,6 @@ static int aspeed_adc_probe(struct platform_device *pdev)
>  			goto poll_timeout_error;
>  	}
>  
> -	ret = clk_prepare_enable(data->clk_scaler->clk);
> -	if (ret)
> -		goto clk_enable_error;
>  	adc_engine_control_reg_val =
>  		readl(data->base + ASPEED_REG_ENGINE_CONTROL);
>  	/* Start all channels in normal mode. */
> @@ -354,8 +372,8 @@ static int aspeed_adc_probe(struct platform_device *pdev)
>  iio_register_error:
>  	writel(ASPEED_ADC_OPERATION_MODE_POWER_DOWN,
>  		data->base + ASPEED_REG_ENGINE_CONTROL);
> -	clk_disable_unprepare(data->clk_scaler->clk);
>  vref_config_error:
> +	clk_disable_unprepare(data->clk_scaler->clk);
>  clk_enable_error:
>  poll_timeout_error:
>  	reset_control_assert(data->rst);