Re: [PATCH] iio: adc: rockchip_saradc: just get referenced voltage once at probe

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

On Mon, 2 Aug 2021 17:09:29 +0800
Simon Xue <xxm@rock-chips.com> wrote:

> From: David Wu <david.wu@rock-chips.com>
> 
> The referenced voltage is not changed after initiation, so just only
> get referenced voltage once.
Hi David,

Isn't this an external reference voltage?  If so how do you know
it is not changed at runtime?  It might be unlikely and not happen
on particular platforms, but that's not he same as saying it can never
happen.  Clearly it's racey anyway if that does happen, but we definitely
don't expect frequent voltage changes.

Jonathan

> 
> Signed-off-by: Simon Xue <xxm@rock-chips.com>
> Signed-off-by: David Wu <david.wu@rock-chips.com>
> ---
>  drivers/iio/adc/rockchip_saradc.c | 16 +++++++++-------
>  1 file changed, 9 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/iio/adc/rockchip_saradc.c b/drivers/iio/adc/rockchip_saradc.c
> index f3eb8d2e50dc..cd33c0b9d3eb 100644
> --- a/drivers/iio/adc/rockchip_saradc.c
> +++ b/drivers/iio/adc/rockchip_saradc.c
> @@ -49,6 +49,7 @@ struct rockchip_saradc {
>  	struct clk		*clk;
>  	struct completion	completion;
>  	struct regulator	*vref;
> +	int			uv_vref;
>  	struct reset_control	*reset;
>  	const struct rockchip_saradc_data *data;
>  	u16			last_val;
> @@ -105,13 +106,7 @@ static int rockchip_saradc_read_raw(struct iio_dev *indio_dev,
>  		mutex_unlock(&indio_dev->mlock);
>  		return IIO_VAL_INT;
>  	case IIO_CHAN_INFO_SCALE:
> -		ret = regulator_get_voltage(info->vref);
> -		if (ret < 0) {
> -			dev_err(&indio_dev->dev, "failed to get voltage\n");
> -			return ret;
> -		}
> -
> -		*val = ret / 1000;
> +		*val = info->uv_vref / 1000;
>  		*val2 = chan->scan_type.realbits;
>  		return IIO_VAL_FRACTIONAL_LOG2;
>  	default:
> @@ -410,6 +405,13 @@ static int rockchip_saradc_probe(struct platform_device *pdev)
>  		return ret;
>  	}
>  
> +	info->uv_vref = regulator_get_voltage(info->vref);
> +	if (info->uv_vref < 0) {
> +		dev_err(&pdev->dev, "failed to get voltage\n");
> +		ret = info->uv_vref;
> +		return ret;
> +	}
> +
>  	ret = clk_prepare_enable(info->pclk);
>  	if (ret < 0) {
>  		dev_err(&pdev->dev, "failed to enable pclk\n");