Re: [PATCH v1 2/2] iio: adc: hx711: add support for HX710B
From: Piyush Patle
Date: Sun Apr 19 2026 - 05:14:50 EST
On Sun, Apr 19, 2026 at 3:35 AM David Lechner <dlechner@xxxxxxxxxxxx> wrote:
>
> When there is more than one patch in a series, add a cover letter to
> keep the patches together.
>
A cover letter was included, but it seems it did not reach properly.
I will resend the series with correct threading in v2.
> On 4/18/26 12:06 PM, Piyush Patle wrote:
> > Refactor the driver around per-chip configuration so HX711 and HX710B
> > can share the same core.
> >
> > Add HX710B channel definitions, pulse-count based channel selection, a
>
> Can you explain this difference a bit more? It seems like the two chips
> are quite different in this regard.
>
On HX711, the number of trailing SCK pulses (1–3) after a conversion
selects both the channel and gain for the next measurement.
On HX710B, the gain is fixed and the trailing pulses only select the
channel: 1 pulse selects the differential input channel (10 SPS)
& 2 pulses select the DVDD-AVDD measurement channel (40 SPS)
I will make this distinction clearer in the commit message in v2.
> > variant-specific iio_info, and fixed-scale handling at probe. Update the
> > Kconfig text and trim comments so the added support stays focused on the
> > actual driver behavior.
> >
> > Signed-off-by: Piyush Patle <piyushpatle228@xxxxxxxxx>
> > ---
> > drivers/iio/adc/Kconfig | 9 +-
> > drivers/iio/adc/hx711.c | 222 ++++++++++++++++++++++++++++++++--------
> > 2 files changed, 184 insertions(+), 47 deletions(-)
> >
> > diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
> > index 60038ae8dfc4..ddf981fa72a2 100644
> > --- a/drivers/iio/adc/Kconfig
> > +++ b/drivers/iio/adc/Kconfig
> > @@ -784,18 +784,21 @@ config HI8435
> > called hi8435.
> >
> > config HX711
> > - tristate "AVIA HX711 ADC for weight cells"
> > + tristate "AVIA HX711 and HX710B ADC"
> > depends on GPIOLIB
> > select IIO_BUFFER
> > select IIO_TRIGGERED_BUFFER
> > help
> > - If you say yes here you get support for AVIA HX711 ADC which is used
> > - for weigh cells
> > + If you say yes here you get support for AVIA HX711 and HX710B ADCs
> > + which are used for bridge sensors such as weigh cells.
> >
> > This driver uses two GPIOs, one acts as the clock and controls the
> > channel selection and gain, the other one is used for the measurement
> > data
> >
> > + The HX710B is a variant with fixed gain and a different channel
> > + selection scheme.
> > +
> > Currently the raw value is read from the chip and delivered.
> > To get an actual weight one needs to subtract the
> > zero offset and multiply by a scale factor.
> > diff --git a/drivers/iio/adc/hx711.c b/drivers/iio/adc/hx711.c
> > index 1db8b68a8f64..cd251fa9f6b7 100644
> > --- a/drivers/iio/adc/hx711.c
> > +++ b/drivers/iio/adc/hx711.c
> > @@ -1,6 +1,6 @@
> > // SPDX-License-Identifier: GPL-2.0-or-later
> > /*
> > - * HX711: analog to digital converter for weight sensor module
> > + * HX711/HX710B ADC driver
> > *
> > * Copyright (c) 2016 Andreas Klinger <ak@xxxxxxxxxxxxx>
> > */
> > @@ -76,13 +76,34 @@ static int hx711_get_scale_to_gain(int scale)
> > return -EINVAL;
> > }
> >
> > +/**
> > + * struct hx711_chip_info - per-variant static configuration
> > + * @name: IIO device name
> > + * @channels: channel specification
> > + * @num_channels: number of channels
> > + * @chan_pulse_count: trailing pulse count for fixed-gain variants
> > + * @num_chan_pulses: number of pulse-count entries
> > + * @reset_channel: default channel after reset
> > + */
> > +struct hx711_chip_info {
> > + const char *name;
> > + const struct iio_chan_spec *channels;
> > + int num_channels;
> > + const int *chan_pulse_count;
> > + int num_chan_pulses;
> > + int reset_channel;
> > +};
> > +
> > struct hx711_data {
> > - struct device *dev;
> > - struct gpio_desc *gpiod_pd_sck;
> > - struct gpio_desc *gpiod_dout;
> > - int gain_set; /* gain set on device */
> > - int gain_chan_a; /* gain for channel A */
> > - struct mutex lock;
> > + struct device *dev;
> > + struct gpio_desc *gpiod_pd_sck;
> > + struct gpio_desc *gpiod_dout;
> > + int gain_set; /* HX711 */
> > + int gain_chan_a; /* HX711 channel A gain */
> > + int channel_set; /* HX710B */
> > + int scale; /* HX710B scale */
> > + const struct hx711_chip_info *chip_info;
> > + struct mutex lock;
> > /*
> > * triggered buffer
> > * 2x32-bit channel + 64-bit naturally aligned timestamp
> > @@ -92,13 +113,10 @@ struct hx711_data {
> > aligned_s64 timestamp;
> > } buffer;
> > /*
> > - * delay after a rising edge on SCK until the data is ready DOUT
> > - * this is dependent on the hx711 where the datasheet tells a
> > - * maximum value of 100 ns
> > - * but also on potential parasitic capacities on the wiring
> > + * Delay after SCK rising edge before sampling DOUT.
> > */
> > - u32 data_ready_delay_ns;
> > - u32 clock_frequency;
> > + u32 data_ready_delay_ns;
> > + u32 clock_frequency;
> > };
> >
> > static int hx711_cycle(struct hx711_data *hx711_data)
> > @@ -139,7 +157,11 @@ static int hx711_cycle(struct hx711_data *hx711_data)
> > return gpiod_get_value(hx711_data->gpiod_dout);
> > }
> >
> > -static int hx711_read(struct hx711_data *hx711_data)
> > +/*
> > + * Clock out 24 data bits and then send trailing pulses to select the
> > + * next channel/gain state.
> > + */
> > +static int hx711_read(struct hx711_data *hx711_data, int trailing_pulses)
> > {
> > int i, ret;
> > int value = 0;
> > @@ -158,7 +180,7 @@ static int hx711_read(struct hx711_data *hx711_data)
> >
> > value ^= 0x800000;
> >
> > - for (i = 0; i < hx711_get_gain_to_pulse(hx711_data->gain_set); i++)
> > + for (i = 0; i < trailing_pulses; i++)
> > hx711_cycle(hx711_data);
> >
> > return value;
> > @@ -188,6 +210,7 @@ static int hx711_wait_for_ready(struct hx711_data *hx711_data)
> >
> > static int hx711_reset(struct hx711_data *hx711_data)
> > {
> > + const struct hx711_chip_info *info = hx711_data->chip_info;
> > int val = hx711_wait_for_ready(hx711_data);
> >
> > if (val) {
> > @@ -206,13 +229,17 @@ static int hx711_reset(struct hx711_data *hx711_data)
> >
> > val = hx711_wait_for_ready(hx711_data);
> >
> > - /* after a reset the gain is 128 */
> > - hx711_data->gain_set = HX711_RESET_GAIN;
> > + /* Restore variant default after reset. */
> > + if (info->chan_pulse_count)
> > + hx711_data->channel_set = info->reset_channel;
> > + else
> > + hx711_data->gain_set = HX711_RESET_GAIN;
> > }
> >
> > return val;
> > }
> >
> > +/* Select HX711 channel/gain for the next conversion. */
> > static int hx711_set_gain_for_channel(struct hx711_data *hx711_data, int chan)
> > {
> > int ret;
> > @@ -221,7 +248,8 @@ static int hx711_set_gain_for_channel(struct hx711_data *hx711_data, int chan)
> > if (hx711_data->gain_set == 32) {
> > hx711_data->gain_set = hx711_data->gain_chan_a;
> >
> > - ret = hx711_read(hx711_data);
> > + ret = hx711_read(hx711_data,
> > + hx711_get_gain_to_pulse(hx711_data->gain_set));
> > if (ret < 0)
> > return ret;
> >
> > @@ -233,7 +261,8 @@ static int hx711_set_gain_for_channel(struct hx711_data *hx711_data, int chan)
> > if (hx711_data->gain_set != 32) {
> > hx711_data->gain_set = 32;
> >
> > - ret = hx711_read(hx711_data);
> > + ret = hx711_read(hx711_data,
> > + hx711_get_gain_to_pulse(hx711_data->gain_set));
> > if (ret < 0)
> > return ret;
> >
> > @@ -246,27 +275,52 @@ static int hx711_set_gain_for_channel(struct hx711_data *hx711_data, int chan)
> > return 0;
> > }
> >
> > +/* Select HX710B channel for the next conversion. */
> > +static int hx710b_set_channel(struct hx711_data *hx711_data, int chan)
> > +{
> > + const struct hx711_chip_info *info = hx711_data->chip_info;
> > + int ret;
> > +
> > + if (chan >= info->num_chan_pulses)
> > + return -EINVAL;
> > +
> > + if (hx711_data->channel_set == chan)
> > + return 0;
> > +
> > + hx711_data->channel_set = chan;
> > +
> > + ret = hx711_read(hx711_data, info->chan_pulse_count[chan]);
> > + if (ret < 0)
> > + return ret;
> > +
> > + return hx711_wait_for_ready(hx711_data);
> > +}
> > +
> > static int hx711_reset_read(struct hx711_data *hx711_data, int chan)
> > {
> > + const struct hx711_chip_info *info = hx711_data->chip_info;
> > + int trailing_pulses;
> > int ret;
> > - int val;
> >
> > - /*
> > - * hx711_reset() must be called from here
> > - * because it could be calling hx711_read() by itself
> > - */
> > + /* Reset first so the read starts from a known chip state. */
> > if (hx711_reset(hx711_data)) {
> > dev_err(hx711_data->dev, "reset failed!");
> > return -EIO;
> > }
> >
> > - ret = hx711_set_gain_for_channel(hx711_data, chan);
> > - if (ret < 0)
> > - return ret;
> > -
> > - val = hx711_read(hx711_data);
> > + if (info->chan_pulse_count) {
> > + ret = hx710b_set_channel(hx711_data, chan);
> > + if (ret < 0)
> > + return ret;
> > + trailing_pulses = info->chan_pulse_count[chan];
> > + } else {
> > + ret = hx711_set_gain_for_channel(hx711_data, chan);
> > + if (ret < 0)
> > + return ret;
> > + trailing_pulses = hx711_get_gain_to_pulse(hx711_data->gain_set);
> > + }
> >
> > - return val;
> > + return hx711_read(hx711_data, trailing_pulses);
> > }
> >
> > static int hx711_read_raw(struct iio_dev *indio_dev,
> > @@ -274,6 +328,7 @@ static int hx711_read_raw(struct iio_dev *indio_dev,
> > int *val, int *val2, long mask)
> > {
> > struct hx711_data *hx711_data = iio_priv(indio_dev);
> > + const struct hx711_chip_info *info = hx711_data->chip_info;
> >
> > switch (mask) {
> > case IIO_CHAN_INFO_RAW:
> > @@ -290,7 +345,10 @@ 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);
> > + if (info->chan_pulse_count)
> > + *val2 = hx711_data->scale;
> > + else
> > + *val2 = hx711_get_gain_to_scale(hx711_data->gain_set);
> >
> > mutex_unlock(&hx711_data->lock);
> >
> > @@ -332,7 +390,8 @@ static int hx711_write_raw(struct iio_dev *indio_dev,
> > if (gain != 32)
> > hx711_data->gain_chan_a = gain;
> >
> > - ret = hx711_read(hx711_data);
> > + ret = hx711_read(hx711_data,
> > + hx711_get_gain_to_pulse(hx711_data->gain_set));
> > if (ret < 0) {
> > mutex_unlock(&hx711_data->lock);
> > return ret;
> > @@ -423,6 +482,10 @@ static const struct iio_info hx711_iio_info = {
> > .attrs = &hx711_attribute_group,
> > };
> >
> > +static const struct iio_info hx710b_iio_info = {
> > + .read_raw = hx711_read_raw,
> > +};
> > +
> > static const struct iio_chan_spec hx711_chan_spec[] = {
> > {
> > .type = IIO_VOLTAGE,
> > @@ -455,10 +518,69 @@ static const struct iio_chan_spec hx711_chan_spec[] = {
> > IIO_CHAN_SOFT_TIMESTAMP(2),
> > };
> >
> > +/* HX710B channels: differential input and DVDD-AVDD measurement. */
> > +static const struct iio_chan_spec hx710b_chan_spec[] = {
> > + {
> > + .type = IIO_VOLTAGE,
> > + .channel = 0,
> > + .indexed = 1,
>
> If it is differential, shouldn't we have .differential = 1 and .channel2 = 1?
>
Yes, good catch. I will add .differential = 1 and .channel2 = 1 for
channel 0 in v2.
> > + .info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
> > + BIT(IIO_CHAN_INFO_SCALE),
> > + .scan_index = 0,
> > + .scan_type = {
> > + .sign = 'u',
> > + .realbits = 24,
> > + .storagebits = 32,
> > + .endianness = IIO_CPU,
> > + },
> > + },
> > + {
> > + .type = IIO_VOLTAGE,
> > + .channel = 1,
> > + .indexed = 1,
> > + .info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
> > + BIT(IIO_CHAN_INFO_SCALE),
> > + .scan_index = 1,
> > + .scan_type = {
> > + .sign = 'u',
> > + .realbits = 24,
> > + .storagebits = 32,
> > + .endianness = IIO_CPU,
> > + },
> > + },
> > + IIO_CHAN_SOFT_TIMESTAMP(2),
> > +};
> > +
> > +/*
> > + * HX710B trailing pulse counts.
> > + * 25 selects differential input, 26 selects DVDD-AVDD.
> > + */
> > +static const int hx710b_pulse_counts[] = {
> > + 25, /* channel 0: differential input, 10 SPS */
> > + 26, /* channel 1: DVDD-AVDD voltage, 40 SPS */
>
> We could store these numbers in the .address field of the channel
> instead. It is there for driver-specific things like this.
>
Agreed. I will store the trailing pulse counts in chan->address and
remove the separate array in v2.
> > +};
> > +
> > +static const struct hx711_chip_info hx711_chip = {
> > + .name = "hx711",
> > + .channels = hx711_chan_spec,
> > + .num_channels = ARRAY_SIZE(hx711_chan_spec),
> > + .chan_pulse_count = NULL,
> > +};
> > +
> > +static const struct hx711_chip_info hx710b_chip = {
> > + .name = "hx710b",
> > + .channels = hx710b_chan_spec,
> > + .num_channels = ARRAY_SIZE(hx710b_chan_spec),
> > + .chan_pulse_count = hx710b_pulse_counts,
> > + .num_chan_pulses = ARRAY_SIZE(hx710b_pulse_counts),
> > + .reset_channel = 0,
> > +};
> > +
> > static int hx711_probe(struct platform_device *pdev)
> > {
> > struct device *dev = &pdev->dev;
> > struct hx711_data *hx711_data;
> > + const struct hx711_chip_info *chip_info;
> > struct iio_dev *indio_dev;
> > int ret;
> > int i;
> > @@ -472,6 +594,11 @@ static int hx711_probe(struct platform_device *pdev)
> >
> > mutex_init(&hx711_data->lock);
> >
> > + chip_info = device_get_match_data(dev);
> > + if (!chip_info)
> > + return -ENODEV;
>
> We recently decided to standardize on not checking for NULL on this.
>
Got it, I will remove the NULL check in v2.
> > + hx711_data->chip_info = chip_info;
> > +
> > /*
> > * PD_SCK stands for power down and serial clock input of HX711
> > * in the driver it is an output
> > @@ -510,12 +637,20 @@ static int hx711_probe(struct platform_device *pdev)
> > /* we need 10^-9 mV */
> > ret *= 100;
> >
> > - for (i = 0; i < HX711_GAIN_MAX; i++)
> > - hx711_gain_to_scale[i].scale =
> > - ret / hx711_gain_to_scale[i].gain / 1678;
> > + if (chip_info->chan_pulse_count) {
>
> Why does chan_pulse_count imply fixed gain? If it is not related, we should
> add a new flag to the chip info instead.
>
My initial reasoning was that chan_pulse_count is only used for variants
where channel selection is driven entirely by trailing pulses and no
gain configuration is exposed to the driver, so it implicitly indicated
a fixed-gain device.
However, this conflates channel selection and gain handling, which are
independent concerns and may not scale well for future variants.
I will rework this in v2 by introducing a dedicated fixed gain flag in
the chip info.
> We want to avoid assuming any branch of the if statement is a specific chip
> in case any more are added in the future.
>
Also, while reviewing this, I noticed that the pulse counts were
incorrectly specified as 25/26. Since hx711_read() already clocks out
24 data bits, trailing_pulses should represent only the additional
cycles after data, so the correct values are 1 and 2. This will be
fixed in v2.
> > + /* HX710B uses a fixed gain, so compute scale once at probe. */
> > + hx711_data->scale = ret / 128 / 1678;
> > + hx711_data->channel_set = chip_info->reset_channel;
> > + indio_dev->info = &hx710b_iio_info;
> > + } else {
> > + for (i = 0; i < HX711_GAIN_MAX; i++)
> > + hx711_gain_to_scale[i].scale =
> > + ret / hx711_gain_to_scale[i].gain / 1678;
> >
> > - hx711_data->gain_set = 128;
> > - hx711_data->gain_chan_a = 128;
> > + hx711_data->gain_set = 128;
> > + hx711_data->gain_chan_a = 128;
> > + indio_dev->info = &hx711_iio_info;
> > + }
> >
> > hx711_data->clock_frequency = 400000;
> > ret = device_property_read_u32(&pdev->dev, "clock-frequency",
> > @@ -533,11 +668,10 @@ static int hx711_probe(struct platform_device *pdev)
> > hx711_data->data_ready_delay_ns =
> > 1000000000 / hx711_data->clock_frequency;
> >
> > - indio_dev->name = "hx711";
> > - indio_dev->info = &hx711_iio_info;
> > + indio_dev->name = chip_info->name;
> > indio_dev->modes = INDIO_DIRECT_MODE;
> > - indio_dev->channels = hx711_chan_spec;
> > - indio_dev->num_channels = ARRAY_SIZE(hx711_chan_spec);
> > + indio_dev->channels = chip_info->channels;
> > + indio_dev->num_channels = chip_info->num_channels;
> >
> > ret = devm_iio_triggered_buffer_setup(dev, indio_dev,
> > iio_pollfunc_store_time,
> > @@ -554,7 +688,8 @@ static int hx711_probe(struct platform_device *pdev)
> > }
> >
> > static const struct of_device_id of_hx711_match[] = {
> > - { .compatible = "avia,hx711", },
> > + { .compatible = "avia,hx711", .data = &hx711_chip },
> > + { .compatible = "avia,hx710b", .data = &hx710b_chip },
> > { }
> > };
> >
> > @@ -571,7 +706,6 @@ static struct platform_driver hx711_driver = {
> > module_platform_driver(hx711_driver);
> >
> > MODULE_AUTHOR("Andreas Klinger <ak@xxxxxxxxxxxxx>");
> > -MODULE_DESCRIPTION("HX711 bitbanging driver - ADC for weight cells");
> > +MODULE_DESCRIPTION("HX711/HX710B GPIO ADC driver");
> > MODULE_LICENSE("GPL");
> > MODULE_ALIAS("platform:hx711-gpio");
> > -
>