// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * HX711: analog to digital converter for weight sensor module
 *
 * Copyright (c) 2016 Andreas Klinger <ak@it-klinger.de>
 */
#include <linux/err.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/mod_devicetable.h>
#include <linux/platform_device.h>
#include <linux/property.h>
#include <linux/slab.h>
#include <linux/sched.h>
#include <linux/delay.h>
#include <linux/iio/iio.h>
#include <linux/iio/sysfs.h>
#include <linux/iio/buffer.h>
#include <linux/iio/trigger_consumer.h>
#include <linux/iio/triggered_buffer.h>
#include <linux/gpio/consumer.h>
#include <linux/regulator/consumer.h>

/* gain to pulse and scale conversion */
#define HX711_GAIN_MAX          3
#define HX711_RESET_GAIN        128

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()
 *
 * 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 int hx711_get_gain_to_pulse(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].gain_pulse;
        return 1;
}

static int hx711_get_gain_to_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 0;
}

static int hx711_get_scale_to_gain(int scale)
{
        int i;

        for (i = 0; i < HX711_GAIN_MAX; i++)
                if (hx711_gain_to_scale[i].scale == scale)
                        return hx711_gain_to_scale[i].gain;
        return -EINVAL;
}

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;
        /*
         * triggered buffer
         * 2x32-bit channel + 64-bit naturally aligned timestamp
         */
        struct {
                u32 channel[2];
                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
         */
        u32                     data_ready_delay_ns;
        u32                     clock_frequency;
};

static int hx711_cycle(struct hx711_data *hx711_data)
{
        unsigned long flags;

        /*
         * if preempted for more then 60us while PD_SCK is high:
         * hx711 is going in reset
         * ==> measuring is false
         */
        local_irq_save(flags);
        gpiod_set_value(hx711_data->gpiod_pd_sck, 1);

        /*
         * wait until DOUT is ready
         * it turned out that parasitic capacities are extending the time
         * until DOUT has reached it's value
         */
        ndelay(hx711_data->data_ready_delay_ns);

        /*
         * here we are not waiting for 0.2 us as suggested by the datasheet,
         * because the oscilloscope showed in a test scenario
         * at least 1.15 us for PD_SCK high (T3 in datasheet)
         * and 0.56 us for PD_SCK low on TI Sitara with 800 MHz
         */
        gpiod_set_value(hx711_data->gpiod_pd_sck, 0);
        local_irq_restore(flags);

        /*
         * make it a square wave for addressing cases with capacitance on
         * PC_SCK
         */
        ndelay(hx711_data->data_ready_delay_ns);

        /* sample as late as possible */
        return gpiod_get_value(hx711_data->gpiod_dout);
}

static int hx711_read(struct hx711_data *hx711_data)
{
        int i, ret;
        int value = 0;
        int val = gpiod_get_value(hx711_data->gpiod_dout);

        /* we double check if it's really down */
        if (val)
                return -EIO;

        for (i = 0; i < 24; i++) {
                value <<= 1;
                ret = hx711_cycle(hx711_data);
                if (ret)
                        value++;
        }

        value ^= 0x800000;

        for (i = 0; i < hx711_get_gain_to_pulse(hx711_data->gain_set); i++)
                hx711_cycle(hx711_data);

        return value;
}

static int hx711_wait_for_ready(struct hx711_data *hx711_data)
{
        int i, val;

        /*
         * in some rare cases the reset takes quite a long time
         * especially when the channel is changed.
         * Allow up to one second for it
         */
        for (i = 0; i < 100; i++) {
                val = gpiod_get_value(hx711_data->gpiod_dout);
                if (!val)
                        break;
                /* sleep at least 10 ms */
                msleep(10);
        }
        if (val)
                return -EIO;

        return 0;
}

static int hx711_reset(struct hx711_data *hx711_data)
{
        int val = hx711_wait_for_ready(hx711_data);

        if (val) {
                /*
                 * an examination with the oszilloscope indicated
                 * that the first value read after the reset is not stable
                 * if we reset too short;
                 * the shorter the reset cycle
                 * the less reliable the first value after reset is;
                 * there were no problems encountered with a value
                 * of 10 ms or higher
                 */
                gpiod_set_value(hx711_data->gpiod_pd_sck, 1);
                msleep(10);
                gpiod_set_value(hx711_data->gpiod_pd_sck, 0);

                val = hx711_wait_for_ready(hx711_data);

                /* after a reset the gain is 128 */
                hx711_data->gain_set = HX711_RESET_GAIN;
        }

        return val;
}

static int hx711_set_gain_for_channel(struct hx711_data *hx711_data, int chan)
{
        int ret;

        if (chan == 0) {
                if (hx711_data->gain_set == 32) {
                        hx711_data->gain_set = hx711_data->gain_chan_a;

                        ret = hx711_read(hx711_data);
                        if (ret < 0)
                                return ret;

                        ret = hx711_wait_for_ready(hx711_data);
                        if (ret)
                                return ret;
                }
        } else {
                if (hx711_data->gain_set != 32) {
                        hx711_data->gain_set = 32;

                        ret = hx711_read(hx711_data);
                        if (ret < 0)
                                return ret;

                        ret = hx711_wait_for_ready(hx711_data);
                        if (ret)
                                return ret;
                }
        }

        return 0;
}

static int hx711_reset_read(struct hx711_data *hx711_data, int chan)
{
        int ret;
        int val;

        /*
         * hx711_reset() must be called from here
         * because it could be calling hx711_read() by itself
         */
        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);

        return val;
}

static int hx711_read_raw(struct iio_dev *indio_dev,
                                const struct iio_chan_spec *chan,
                                int *val, int *val2, long mask)
{
        struct hx711_data *hx711_data = iio_priv(indio_dev);

        switch (mask) {
        case IIO_CHAN_INFO_RAW:
                mutex_lock(&hx711_data->lock);

                *val = hx711_reset_read(hx711_data, chan->channel);

                mutex_unlock(&hx711_data->lock);

                if (*val < 0)
                        return *val;
                return IIO_VAL_INT;
        case IIO_CHAN_INFO_SCALE:
                *val = 0;
                mutex_lock(&hx711_data->lock);

                *val2 = hx711_get_gain_to_scale(hx711_data->gain_set);

                mutex_unlock(&hx711_data->lock);

                return IIO_VAL_INT_PLUS_NANO;
        default:
                return -EINVAL;
        }
}

static int hx711_write_raw(struct iio_dev *indio_dev,
                                struct iio_chan_spec const *chan,
                                int val,
                                int val2,
                                long mask)
{
        struct hx711_data *hx711_data = iio_priv(indio_dev);
        int ret;
        int gain;

        switch (mask) {
        case IIO_CHAN_INFO_SCALE:
                /*
                 * a scale greater than 1 mV per LSB is not possible
                 * with the HX711, therefore val must be 0
                 */
                if (val != 0)
                        return -EINVAL;

                mutex_lock(&hx711_data->lock);

                gain = hx711_get_scale_to_gain(val2);
                if (gain < 0) {
                        mutex_unlock(&hx711_data->lock);
                        return gain;
                }

                if (gain != hx711_data->gain_set) {
                        hx711_data->gain_set = gain;
                        if (gain != 32)
                                hx711_data->gain_chan_a = gain;

                        ret = hx711_read(hx711_data);
                        if (ret < 0) {
                                mutex_unlock(&hx711_data->lock);
                                return ret;
                        }
                }

                mutex_unlock(&hx711_data->lock);
                return 0;
        default:
                return -EINVAL;
        }

        return 0;
}

static int hx711_write_raw_get_fmt(struct iio_dev *indio_dev,
                struct iio_chan_spec const *chan,
                long mask)
{
        return IIO_VAL_INT_PLUS_NANO;
}

static irqreturn_t hx711_trigger(int irq, void *p)
{
        struct iio_poll_func *pf = p;
        struct iio_dev *indio_dev = pf->indio_dev;
        struct hx711_data *hx711_data = iio_priv(indio_dev);
        int i, j = 0;

        mutex_lock(&hx711_data->lock);

        memset(&hx711_data->buffer, 0, sizeof(hx711_data->buffer));

        iio_for_each_active_channel(indio_dev, i) {
                hx711_data->buffer.channel[j] = hx711_reset_read(hx711_data,
                                        indio_dev->channels[i].channel);
                j++;
        }

        iio_push_to_buffers_with_timestamp(indio_dev, &hx711_data->buffer,
                                                        pf->timestamp);

        mutex_unlock(&hx711_data->lock);

        iio_trigger_notify_done(indio_dev->trig);

        return IRQ_HANDLED;
}

static ssize_t hx711_scale_available_show(struct device *dev,
                                struct device_attribute *attr,
                                char *buf)
{
        struct iio_dev_attr *iio_attr = to_iio_dev_attr(attr);
        int channel = iio_attr->address;
        int i, len = 0;

        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);

        len += sprintf(buf + len, "\n");

        return len;
}

static IIO_DEVICE_ATTR(in_voltage0_scale_available, S_IRUGO,
        hx711_scale_available_show, NULL, 0);

static IIO_DEVICE_ATTR(in_voltage1_scale_available, S_IRUGO,
        hx711_scale_available_show, NULL, 1);

static struct attribute *hx711_attributes[] = {
        &iio_dev_attr_in_voltage0_scale_available.dev_attr.attr,
        &iio_dev_attr_in_voltage1_scale_available.dev_attr.attr,
        NULL,
};

static const struct attribute_group hx711_attribute_group = {
        .attrs = hx711_attributes,
};

static const struct iio_info hx711_iio_info = {
        .read_raw               = hx711_read_raw,
        .write_raw              = hx711_write_raw,
        .write_raw_get_fmt      = hx711_write_raw_get_fmt,
        .attrs                  = &hx711_attribute_group,
};

static const struct iio_chan_spec hx711_chan_spec[] = {
        {
                .type = IIO_VOLTAGE,
                .channel = 0,
                .indexed = 1,
                .info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
                .info_mask_shared_by_type = 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),
                .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),
                .scan_index = 1,
                .scan_type = {
                        .sign = 'u',
                        .realbits = 24,
                        .storagebits = 32,
                        .endianness = IIO_CPU,
                },
        },
        IIO_CHAN_SOFT_TIMESTAMP(2),
};

static int hx711_probe(struct platform_device *pdev)
{
        struct device *dev = &pdev->dev;
        struct hx711_data *hx711_data;
        struct iio_dev *indio_dev;
        int ret;
        int i;

        indio_dev = devm_iio_device_alloc(dev, sizeof(struct hx711_data));
        if (!indio_dev)
                return -ENOMEM;

        hx711_data = iio_priv(indio_dev);
        hx711_data->dev = dev;

        mutex_init(&hx711_data->lock);

        /*
         * PD_SCK stands for power down and serial clock input of HX711
         * in the driver it is an output
         */
        hx711_data->gpiod_pd_sck = devm_gpiod_get(dev, "sck", GPIOD_OUT_LOW);
        if (IS_ERR(hx711_data->gpiod_pd_sck))
                return dev_err_probe(dev, PTR_ERR(hx711_data->gpiod_pd_sck),
                                     "failed to get sck-gpiod\n");

        /*
         * DOUT stands for serial data output of HX711
         * for the driver it is an input
         */
        hx711_data->gpiod_dout = devm_gpiod_get(dev, "dout", GPIOD_IN);
        if (IS_ERR(hx711_data->gpiod_dout))
                return dev_err_probe(dev, PTR_ERR(hx711_data->gpiod_dout),
                                     "failed to get dout-gpiod\n");

        ret = devm_regulator_get_enable_read_voltage(dev, "avdd");
        if (ret < 0)
                return ret;

        /*
         * with
         * full scale differential input range: AVDD / GAIN
         * full scale output data: 2^24
         * we can say:
         *     AVDD / GAIN = 2^24
         * therefore:
         *     1 LSB = AVDD / GAIN / 2^24
         * AVDD 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]
         */

        /* 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;

        hx711_data->gain_set = 128;
        hx711_data->gain_chan_a = 128;

        hx711_data->clock_frequency = 400000;
        ret = device_property_read_u32(&pdev->dev, "clock-frequency",
                                        &hx711_data->clock_frequency);

        /*
         * datasheet says the high level of PD_SCK has a maximum duration
         * of 50 microseconds
         */
        if (hx711_data->clock_frequency < 20000) {
                dev_warn(dev, "clock-frequency too low - assuming 400 kHz\n");
                hx711_data->clock_frequency = 400000;
        }

        hx711_data->data_ready_delay_ns =
                                1000000000 / hx711_data->clock_frequency;

        indio_dev->name = "hx711";
        indio_dev->info = &hx711_iio_info;
        indio_dev->modes = INDIO_DIRECT_MODE;
        indio_dev->channels = hx711_chan_spec;
        indio_dev->num_channels = ARRAY_SIZE(hx711_chan_spec);

        ret = devm_iio_triggered_buffer_setup(dev, indio_dev,
                                              iio_pollfunc_store_time,
                                              hx711_trigger, NULL);
        if (ret < 0)
                return dev_err_probe(dev, ret,
                                     "setup of iio triggered buffer failed\n");

        ret = devm_iio_device_register(dev, indio_dev);
        if (ret < 0)
                return dev_err_probe(dev, ret, "Couldn't register the device\n");

        return 0;
}

static const struct of_device_id of_hx711_match[] = {
        { .compatible = "avia,hx711", },
        { }
};

MODULE_DEVICE_TABLE(of, of_hx711_match);

static struct platform_driver hx711_driver = {
        .probe          = hx711_probe,
        .driver         = {
                .name           = "hx711-gpio",
                .of_match_table = of_hx711_match,
        },
};

module_platform_driver(hx711_driver);

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");