Re: [PATCH v4 7/7] iio: adc: hx711: add support for HX710B

Andy Shevchenko
2026-04-27T14:34:51Z

On Mon, Apr 27, 2026 at 03:39:38PM +0530, Piyush Patle wrote:
> Add support for the AVIA HX710B ADC, which shares the HX711 GPIO
> interface but has a fixed gain of 128 and uses trailing PD_SCK pulses
> to select the active channel rather than the gain.
>
> The HX710B has three operating modes controlled by the trailing pulse
> count after the 24 data bits (Table 3 in the HX710B datasheet):
> 25 pulses (1 trailing): differential input at 10 SPS
> 26 pulses (2 trailing): DVDD-AVDD supply monitor at 40 SPS
> 27 pulses (3 trailing): differential input at 40 SPS
>
> Model the HX710B with its own hx710b_chan_spec[] and hx710b_iio_info.
> Store the trailing pulse count in chan->address so hx710b_set_channel()
> can switch channels without a separate lookup table. The supply monitor
> uses .channel = 2 to avoid aliasing the channel2 terminal (index 1) of
> the differential pair.
>
> The HX710B has a dedicated VREF pin for the ADC reference voltage. The
> driver tries vref-supply first; if absent it falls back to avdd-supply
> (for boards where VREF is tied to AVDD). The HX711 uses AVDD as its
> reference and is unaffected.
>
> Add fixed_gain and fixed_gain_val fields to hx711_chip_info to carry the
> gain into the scale calculation. Store a per-instance scale in
> hx711_data for HX710B and use it in hx711_read_raw() when fixed_gain is
> set. Update hx711_reset() to reset channel_set on HX710B after a
> power-down cycle.
>
> Enlarge the trigger buffer from 2 to 3 channels plus a pad word to keep
> the timestamp naturally aligned; HX711 continues to use only the first
> two slots.

So, missed types.h should be in this patch.

...

> /**
> * struct hx711_chip_info - per-variant static configuration
> - * @name: IIO device name
> - * @channels: channel specification array
> - * @iio_info: IIO info ops for this variant
> - * @num_channels: number of entries in @channels
> + * @name: IIO device name
> + * @channels: channel specification array
> + * @iio_info: IIO info ops for this variant
> + * @num_channels: number of entries in @channels
> + * @fixed_gain_val: fixed PGA gain (used when @fixed_gain is true)
> + * @fixed_gain: true if the variant has a fixed ADC gain (e.g. HX710B)

No, make sure there will be no '-' lines here.

> */

...

> struct hx711_data {

> int gain_set; /* gain set on device */
> int gain_chan_a; /* gain for channel A */
> int gain_scale[HX711_GAIN_MAX];

> + unsigned int channel_set; /* HX710B active channel */
> const struct hx711_chip_info *chip_info;
> + unsigned int scale; /* HX710B fixed-gain scale */

Semantically the scale is closer to the above gain_* ones AFAICS.

> struct mutex lock;
> /*
> * triggered buffer
> - * 2x32-bit channel + 64-bit naturally aligned timestamp
> + * up to 3x32-bit channels + pad + 64-bit naturally aligned timestamp
> */
> struct {
> - u32 channel[2];
> + u32 channel[3];
> + u32 pad;
> aligned_s64 timestamp;
> } buffer;
> /*

...

> 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) {

The rule of thumb is to split definition and assignment for the variables that
are going to be validated.

Here I expect to see

int val;

val = hx711_wait_for_ready(hx711_data);
if (val) {

But since it's not related directly to this change, make a preparatory patch.
Because now with two variables this looks worse and adds more potential to be
mistaken in the future.

> +static int hx710b_set_channel(struct hx711_data *hx711_data,
> + const struct iio_chan_spec *chan)
> +{
> + int ret;
> +
> + if (hx711_data->channel_set == (unsigned int)chan->channel)
> + return 0;
> +
> + ret = hx711_read(hx711_data, chan->address);
> + if (ret < 0)
> + return ret;
> +
> + ret = hx711_wait_for_ready(hx711_data);
> + if (ret)
> + return ret;
> +
> + hx711_data->channel_set = chan->channel;
> +
> + return 0;
> +}

...

> - ret = hx711_set_gain_for_channel(hx711_data, chan->channel);
> - if (ret < 0)
> - return ret;

> + ret = hx711_set_gain_for_channel(hx711_data, chan->channel);
> + if (ret < 0)
> + return ret;
> + trailing_pulses = hx711_get_gain_to_pulse(hx711_data->gain_set);
> + }
>
> - trailing_pulses = hx711_get_gain_to_pulse(hx711_data->gain_set);
> return hx711_read(hx711_data, trailing_pulses);

Instead of the above, first split these lines to a helper

static int hx711_set_hx711_channel(..., *tp)
{
int ret;

ret = hx711_set_gain_for_channel(hx711_data, chan->channel);
if (ret < 0)
return ret;

*tp = hx711_get_gain_to_pulse(hx711_data->gain_set);
return 0;
}

And name your new function something like

hx711_set_hx710b_channel()

...

> + /*
> + * The HX710B uses the VREF pin as the ADC reference; try vref-supply
> + * first and fall back to avdd-supply when VREF is tied to AVDD on the
> + * board. The HX711 uses AVDD as its reference.

I think we use a single space in the comment, but double check that.
The rule of thumb is to keep the original driver style and change it
separately if required.

> + */

...

> /*
> * with

While at it, with --> With.

> - * full scale differential input range: AVDD / GAIN
> + * full scale differential input range: VREF / GAIN
> * full scale output data: 2^24
> * we can say:
> - * AVDD / GAIN = 2^24
> + * VREF / GAIN = 2^24
> * therefore:
> - * 1 LSB = AVDD / GAIN / 2^24
> - * AVDD is in uV, but we need 10^-9 mV
> + * 1 LSB = VREF / GAIN / 2^24
> + * VREF is in uV, but we need 10^-9 mV
> * approximately to fit into a 32 bit number:
> - * 1 LSB = (AVDD * 100) / GAIN / 1678 [10^-9 mV]
> + * 1 LSB = (VREF * 100) / GAIN / 1678 [10^-9 mV]
> */

...

> - for (i = 0; i < HX711_GAIN_MAX; i++)
> - hx711_data->gain_scale[i] =
> - ret / hx711_gain_to_scale[i].gain / 1678;
> + if (chip_info->fixed_gain) {
> + hx711_data->scale = ret / chip_info->fixed_gain_val / 1678;
> + } else {
> + for (i = 0; i < HX711_GAIN_MAX; i++)
> + hx711_data->gain_scale[i] =
> + 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;
> + }

Looking at this I'm wondering wouldn't be easier just to have the array, but
feel it with the same data.

...

> - { .compatible = "avia,hx711", .data = &hx711_chip },

> + { .compatible = "avia,hx711", .data = &hx711_chip },

Why?! This is stray change.

--
With Best Regards,
Andy Shevchenko