[PATCH v5 05/11] iio: adc: hx711: move scale computation to per-device storage

Piyush Patle
2026-04-29T05:46:15Z

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>
---
Changes in v5:
- Add trailing commas in the hx711_gain_to_scale[] initializers.
- Keep the hx711_data declaration in hx711_scale_available_show() on one
line and preserve local declaration ordering.
Changes in v4:
- New patch added to fix the pre-existing global scale mutation bug
reported during review.
---
drivers/iio/adc/hx711.c | 32 ++++++++++++++++----------------
1 file changed, 16 insertions(+), 16 deletions(-)

diff --git a/drivers/iio/adc/hx711.c b/drivers/iio/adc/hx711.c
index 1db8b68a8f64..8485e18c949d 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;
@@ -574,4 +575,3 @@ MODULE_AUTHOR("Andreas Klinger <ak@it-klinger.de>");
MODULE_DESCRIPTION("HX711 bitbanging driver - ADC for weight cells");
MODULE_LICENSE("GPL");
MODULE_ALIAS("platform:hx711-gpio");
-
--
2.43.0