Re: [PATCH v8 v8 05/11] iio: adc: hx711: move scale computation to per-device storage

[Jonathan Cameron <jic23@kernel.org>]

On Mon, 11 May 2026 23:13:30 +0530
Piyush Patle <piyushpatle228@gmail.com> wrote:

> The gain-to-scale table is global today, so probe-time scale updates for
> one device overwrite the values used by any earlier device instance.
> 
> Fix this by making the gain table const and storing the computed scale
> values per device in hx711_data.
> 
> No functional change for single-sensor configurations.
> 
> Signed-off-by: Piyush Patle <piyushpatle228@gmail.com>
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>

This is a patch that stands fine on it's own (and Sashiko was fine with
v7) so I'll apply it now.

Applied to the testing branch of iio.git.

Thanks,

Jonathan

> ---
>  drivers/iio/adc/hx711.c | 31 ++++++++++++++++---------------
>  1 file changed, 16 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/iio/adc/hx711.c b/drivers/iio/adc/hx711.c
> index 1db8b68a8f64..86d2a70dd3de 100644
> --- a/drivers/iio/adc/hx711.c
> +++ b/drivers/iio/adc/hx711.c
> @@ -28,22 +28,20 @@
>  struct hx711_gain_to_scale {
>  	int			gain;
>  	int			gain_pulse;
> -	int			scale;
>  	int			channel;
>  };
>  
>  /*
>   * .scale depends on AVDD which in turn is known as soon as the regulator
> - * is available
> - * therefore we set .scale in hx711_probe()
> + * is available; it is stored per device in hx711_data.gain_scale[]
>   *
>   * channel A in documentation is channel 0 in source code
>   * channel B in documentation is channel 1 in source code
>   */
> -static struct hx711_gain_to_scale hx711_gain_to_scale[HX711_GAIN_MAX] = {
> -	{ 128, 1, 0, 0 },
> -	{  32, 2, 0, 1 },
> -	{  64, 3, 0, 0 }
> +static const struct hx711_gain_to_scale hx711_gain_to_scale[HX711_GAIN_MAX] = {
> +	{ 128, 1, 0 },
> +	{  32, 2, 1 },
> +	{  64, 3, 0 },
>  };
>  
>  static int hx711_get_gain_to_pulse(int gain)
> @@ -56,22 +54,22 @@ static int hx711_get_gain_to_pulse(int gain)
>  	return 1;
>  }
>  
> -static int hx711_get_gain_to_scale(int gain)
> +static int hx711_get_gain_to_scale(const int *gain_scale, int gain)
>  {
>  	int i;
>  
>  	for (i = 0; i < HX711_GAIN_MAX; i++)
>  		if (hx711_gain_to_scale[i].gain == gain)
> -			return hx711_gain_to_scale[i].scale;
> +			return gain_scale[i];
>  	return 0;
>  }
>  
> -static int hx711_get_scale_to_gain(int scale)
> +static int hx711_get_scale_to_gain(const int *gain_scale, int scale)
>  {
>  	int i;
>  
>  	for (i = 0; i < HX711_GAIN_MAX; i++)
> -		if (hx711_gain_to_scale[i].scale == scale)
> +		if (gain_scale[i] == scale)
>  			return hx711_gain_to_scale[i].gain;
>  	return -EINVAL;
>  }
> @@ -82,6 +80,7 @@ struct hx711_data {
>  	struct gpio_desc	*gpiod_dout;
>  	int			gain_set;	/* gain set on device */
>  	int			gain_chan_a;	/* gain for channel A */
> +	int			gain_scale[HX711_GAIN_MAX];
>  	struct mutex		lock;
>  	/*
>  	 * triggered buffer
> @@ -290,7 +289,8 @@ static int hx711_read_raw(struct iio_dev *indio_dev,
>  		*val = 0;
>  		mutex_lock(&hx711_data->lock);
>  
> -		*val2 = hx711_get_gain_to_scale(hx711_data->gain_set);
> +		*val2 = hx711_get_gain_to_scale(hx711_data->gain_scale,
> +						hx711_data->gain_set);
>  
>  		mutex_unlock(&hx711_data->lock);
>  
> @@ -321,7 +321,7 @@ static int hx711_write_raw(struct iio_dev *indio_dev,
>  
>  		mutex_lock(&hx711_data->lock);
>  
> -		gain = hx711_get_scale_to_gain(val2);
> +		gain = hx711_get_scale_to_gain(hx711_data->gain_scale, val2);
>  		if (gain < 0) {
>  			mutex_unlock(&hx711_data->lock);
>  			return gain;
> @@ -386,6 +386,7 @@ static ssize_t hx711_scale_available_show(struct device *dev,
>  				struct device_attribute *attr,
>  				char *buf)
>  {
> +	struct hx711_data *hx711_data = iio_priv(dev_to_iio_dev(dev));
>  	struct iio_dev_attr *iio_attr = to_iio_dev_attr(attr);
>  	int channel = iio_attr->address;
>  	int i, len = 0;
> @@ -393,7 +394,7 @@ static ssize_t hx711_scale_available_show(struct device *dev,
>  	for (i = 0; i < HX711_GAIN_MAX; i++)
>  		if (hx711_gain_to_scale[i].channel == channel)
>  			len += sprintf(buf + len, "0.%09d ",
> -					hx711_gain_to_scale[i].scale);
> +				       hx711_data->gain_scale[i]);
>  
>  	len += sprintf(buf + len, "\n");
>  
> @@ -511,7 +512,7 @@ static int hx711_probe(struct platform_device *pdev)
>  	ret *= 100;
>  
>  	for (i = 0; i < HX711_GAIN_MAX; i++)
> -		hx711_gain_to_scale[i].scale =
> +		hx711_data->gain_scale[i] =
>  			ret / hx711_gain_to_scale[i].gain / 1678;
>  
>  	hx711_data->gain_set = 128;