linux-kernel - Re: [RESEND v4 12/15] iio: adc: aspeed: Add func to set sampling rate.

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Message-ID: <20210829163659.2f7f5974@jic23-huawei>
Date:   Sun, 29 Aug 2021 16:36:59 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Billy Tsai <billy_tsai@...eedtech.com>
Cc:     <lars@...afoo.de>, <pmeerw@...erw.net>, <robh+dt@...nel.org>,
        <joel@....id.au>, <andrew@...id.au>, <p.zabel@...gutronix.de>,
        <lgirdwood@...il.com>, <broonie@...nel.org>,
        <linux-iio@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-aspeed@...ts.ozlabs.org>, <linux-kernel@...r.kernel.org>,
        <BMC-SW@...eedtech.com>
Subject: Re: [RESEND v4 12/15] iio: adc: aspeed: Add func to set sampling
 rate.

On Tue, 24 Aug 2021 17:12:40 +0800
Billy Tsai <billy_tsai@...eedtech.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@...eedtech.com>

Why move the code as well as factoring out the setter function?
I doubt it does any harm, but I'd like to understand why you did it.

Jonathan


> ---
>  drivers/iio/adc/aspeed_adc.c | 58 +++++++++++++++++++++++++-----------
>  1 file changed, 40 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/iio/adc/aspeed_adc.c b/drivers/iio/adc/aspeed_adc.c
> index 8fe7da1a651f..4d979dd7fe88 100644
> --- a/drivers/iio/adc/aspeed_adc.c
> +++ b/drivers/iio/adc/aspeed_adc.c
> @@ -65,6 +65,12 @@
>  
>  #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
>  
>  struct aspeed_adc_model_data {
>  	const char *model_name;
> @@ -88,6 +94,7 @@ 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) {			\
> @@ -119,6 +126,24 @@ 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);
> +
> +	if (rate < data->model_data->min_sampling_rate ||
> +	    rate > data->model_data->max_sampling_rate)
> +		return -EINVAL;
> +	/* Each sampling needs 12 clocks to covert.*/

convert.  Please run a spell checker over these patches.

> +	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);
> +
> +	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)
> @@ -149,17 +174,10 @@ 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);
>  
>  	switch (mask) {
>  	case IIO_CHAN_INFO_SAMP_FREQ:
> -		if (val < data->model_data->min_sampling_rate ||
> -			val > data->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:
> @@ -386,6 +404,20 @@ static int aspeed_adc_probe(struct platform_device *pdev)
>  	if (ret)
>  		return ret;
>  
> +	ret = clk_prepare_enable(data->clk_scaler->clk);
> +	if (ret)
> +		return ret;
> +
> +	ret = devm_add_action_or_reset(data->dev,
> +				       aspeed_adc_clk_disable_unprepare,
> +				       data->clk_scaler->clk);
> +	if (ret)
> +		return ret;
> +
> +	ret = aspeed_adc_set_sampling_rate(indio_dev, ASPEED_ADC_DEF_SAMPLING_RATE);
> +	if (ret)
> +		return ret;
> +
>  	ret = aspeed_adc_vref_config(indio_dev);
>  	if (ret)
>  		return ret;
> @@ -413,16 +445,6 @@ static int aspeed_adc_probe(struct platform_device *pdev)
>  	}
>  
>  	/* Start all channels in normal mode. */

Why move this code up?

> -	ret = clk_prepare_enable(data->clk_scaler->clk);
> -	if (ret)
> -		return ret;
> -
> -	ret = devm_add_action_or_reset(data->dev,
> -				       aspeed_adc_clk_disable_unprepare,
> -				       data->clk_scaler->clk);
> -	if (ret)
> -		return ret;
> -
>  	adc_engine_control_reg_val =
>  		readl(data->base + ASPEED_REG_ENGINE_CONTROL);
>  	adc_engine_control_reg_val |=