// SPDX-License-Identifier: GPL-2.0+ /* * MAX40080 Digital Current-Sense Amplifier driver * * Copyright 2026 Analog Devices, Inc. * * Datasheet: https://www.analog.com/media/en/technical-documentation/data-sheets/MAX40080.pdf */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #define MAX40080_REG_CFG 0x00 #define MAX40080_CFG_MODE_MSK GENMASK(2, 0) #define MAX40080_CFG_PEC_EN_MSK BIT(5) #define MAX40080_CFG_RANGE_MSK BIT(6) #define MAX40080_CFG_FILTER_MSK GENMASK(14, 12) #define MAX40080_REG_FIFO_CFG 0x0A #define MAX40080_FIFO_CFG_STORE_IV_MSK GENMASK(1, 0) #define MAX40080_REG_IV 0x10 /* Current is a 13-bit two's-complement value (magnitude + sign bit). */ #define MAX40080_IV_I_MSK GENMASK(12, 0) #define MAX40080_IV_I_SIGN_BIT 12 #define MAX40080_IV_V_MAG_MSK GENMASK(27, 16) #define MAX40080_IV_VALID_MSK BIT(31) /* CFG.mode field values. */ #define MAX40080_CFG_MODE_STDBY 0x00 #define MAX40080_CFG_MODE_SINGLE 0x02 /* CFG.range field values. */ #define MAX40080_CFG_RANGE_50mV 0 #define MAX40080_CFG_RANGE_10mV 1 /* FIFO_CFG.store_iv field values. */ #define MAX40080_FIFO_CFG_STORE_IV 0x02 #define MAX40080_ADC_RES_BITS 12 #define MAX40080_INTER_VREF_mV 1250 #define MAX40080_V_BUFF_GAIN 30 #define MAX40080_CSA_50mV_GAIN 25 #define MAX40080_CSA_10mV_GAIN 125 /* * The RANGE field (CFG bit 6) selects one of two current-sense full-scale * ranges (the MAX40080 supports exactly two: +/-50 mV and +/-10 mV). Indexed * by the CFG.range field value. */ static const int max40080_csa_gain[] = { [MAX40080_CFG_RANGE_50mV] = MAX40080_CSA_50mV_GAIN, [MAX40080_CFG_RANGE_10mV] = MAX40080_CSA_10mV_GAIN, }; struct max40080_state { struct i2c_client *client; /* Serializes read-modify-write access to the CFG register. */ struct mutex lock; u32 shunt_resistor_uOhm; /* Cached configuration: the selected RANGE index and oversampling ratio. */ unsigned int range; int oversampling_ratio; /* * Precomputed current scale (mA per code) for each RANGE setting, as * {integer, nano} pairs for IIO_VAL_INT_PLUS_NANO. The range is * selected by writing the corresponding scale. */ int current_scale[2][2]; }; static const int max40080_oversampling_avail[] = { 1, 8, 16, 32, 64, 128 }; static int max40080_update_bits(struct max40080_state *st, u8 reg, u16 mask, u16 val) { int tmp; tmp = i2c_smbus_read_word_data(st->client, reg); if (tmp < 0) return tmp; tmp = (tmp & ~mask) | (val & mask); return i2c_smbus_write_word_data(st->client, reg, tmp); } /* * In single-measurement mode the device sits idle until it receives an SMBus * Quick Command, then performs exactly one current and one voltage conversion * and returns to idle. Triggering on demand this way (rather than running the * FIFO continuously in active mode) means each read returns a fresh, coherent * current/voltage pair instead of the oldest queued FIFO entry. */ static int max40080_trigger_measurement(struct max40080_state *st) { return i2c_smbus_xfer(st->client->adapter, st->client->addr, st->client->flags, I2C_SMBUS_WRITE, 0, I2C_SMBUS_QUICK, NULL); } /* * A single measurement holds the matched current/voltage pair in one 32-bit * word (MAX40080_REG_IV). Reading all four bytes in one transaction returns * both from the same conversion; reading the separate current (0x0C) and * voltage (0x0E) registers would decorrelate the two channels. * * Unlike the word accesses used elsewhere, this is a plain I2C block read: the * SMBus layer does not append or verify a PEC byte for it even when PEC is * otherwise enabled for the device, so this transfer is not PEC protected. */ static int max40080_read_iv_once(struct max40080_state *st, u32 *iv) { __le32 buf = 0; int ret; ret = i2c_smbus_read_i2c_block_data(st->client, MAX40080_REG_IV, sizeof(buf), (u8 *)&buf); if (ret < 0) return ret; *iv = le32_to_cpu(buf); return 0; } static int max40080_read_iv(struct max40080_state *st, u32 *iv) { u32 tmp = 0; int ret, io_ret; guard(mutex)(&st->lock); ret = max40080_trigger_measurement(st); if (ret < 0) return ret; /* * Wait for the conversion to complete by polling the FIFO valid bit * (or bail out on an I2C error). Polling the device's own status makes * this independent of the actual conversion time, which varies with the * oversampling ratio and the bus speed. The timeout is only a safety * ceiling: the worst case is the maximum 128x averaging on both the * current and voltage channels at the slowest 15 ksps base rate plus * the inter-channel switching time, i.e. roughly 20 ms; 50 ms leaves * ample margin. */ ret = read_poll_timeout(max40080_read_iv_once, io_ret, io_ret || (tmp & MAX40080_IV_VALID_MSK), 500, 50 * USEC_PER_MSEC, false, st, &tmp); if (io_ret) return io_ret; /* * Propagate the last-read value even on timeout so the caller can * inspect it for debugging. */ *iv = tmp; return ret; } static int max40080_get_current(struct max40080_state *st, int *val) { u32 iv; int ret; ret = max40080_read_iv(st, &iv); if (ret) return ret; *val = sign_extend32(FIELD_GET(MAX40080_IV_I_MSK, iv), MAX40080_IV_I_SIGN_BIT); return 0; } static int max40080_get_voltage(struct max40080_state *st, int *val) { u32 iv; int ret; ret = max40080_read_iv(st, &iv); if (ret) return ret; *val = FIELD_GET(MAX40080_IV_V_MAG_MSK, iv); return 0; } static int max40080_set_range(struct max40080_state *st, unsigned int range) { int ret; ret = max40080_update_bits(st, MAX40080_REG_CFG, MAX40080_CFG_RANGE_MSK, FIELD_PREP(MAX40080_CFG_RANGE_MSK, range)); if (ret) return ret; WRITE_ONCE(st->range, range); return 0; } /* * Precompute the current scale (mA per code) for each RANGE setting as * {integer, nano} pairs. The shunt drop for a full-scale code is * Vref[mV] / (BIT(ADC_RES_BITS) * gain) * and current = Vshunt / Rshunt, so with Rshunt in micro-ohms the scale in * mA/code is * Vref[mV] * NANO * MICRO / (BIT(ADC_RES_BITS) * gain * Rshunt[uOhm]) * expressed as an integer part plus a nano fractional part. */ static void max40080_calc_current_scale(struct max40080_state *st) { u64 numerator, denominator; u32 rem; for (unsigned int i = 0; i < ARRAY_SIZE(max40080_csa_gain); i++) { numerator = (u64)MAX40080_INTER_VREF_mV * NANO * MICRO; denominator = BIT_ULL(MAX40080_ADC_RES_BITS) * max40080_csa_gain[i] * st->shunt_resistor_uOhm; numerator = div64_u64(numerator, denominator); st->current_scale[i][0] = div_u64_rem(numerator, NANO, &rem); st->current_scale[i][1] = rem; } } /* * max40080_oversampling_avail[] is ordered so that its index is the FILTER * field value (index 0 = no averaging, index 1 = 8x, ...). Return that index * for an exact match, or -EINVAL for a value that is not on the list. */ static int max40080_oversampling_to_filter(int val) { for (unsigned int i = 0; i < ARRAY_SIZE(max40080_oversampling_avail); i++) { if (max40080_oversampling_avail[i] == val) return i; } return -EINVAL; } static int max40080_set_oversampling_ratio(struct max40080_state *st, int val) { int filter; int ret; filter = max40080_oversampling_to_filter(val); if (filter < 0) return filter; ret = max40080_update_bits(st, MAX40080_REG_CFG, MAX40080_CFG_FILTER_MSK, FIELD_PREP(MAX40080_CFG_FILTER_MSK, filter)); if (ret) return ret; WRITE_ONCE(st->oversampling_ratio, val); return 0; } static int max40080_read_raw(struct iio_dev *indio_dev, struct iio_chan_spec const *chan, int *val, int *val2, long mask) { struct max40080_state *st = iio_priv(indio_dev); unsigned int range; int ret; switch (mask) { case IIO_CHAN_INFO_RAW: if (chan->type == IIO_CURRENT) { ret = max40080_get_current(st, val); if (ret) return ret; } else if (chan->type == IIO_VOLTAGE) { ret = max40080_get_voltage(st, val); if (ret) return ret; } return IIO_VAL_INT; case IIO_CHAN_INFO_SCALE: if (chan->type == IIO_CURRENT) { /* * The selectable current-sense range is exposed through * scale: each RANGE setting has its own precomputed * mA-per-code value. Userspace picks the range by * writing the matching scale. * * Use READ_ONCE to ensure the compiler reads st->range * exactly once, so val and val2 come from the same * setting even if a concurrent write changes st->range. */ range = READ_ONCE(st->range); *val = st->current_scale[range][0]; *val2 = st->current_scale[range][1]; return IIO_VAL_INT_PLUS_NANO; } /* voltage[mV] = raw * Vref[mV] * buffer_gain / BIT(ADC_RES_BITS) */ *val = MAX40080_INTER_VREF_mV * MAX40080_V_BUFF_GAIN; *val2 = MAX40080_ADC_RES_BITS; return IIO_VAL_FRACTIONAL_LOG2; case IIO_CHAN_INFO_OVERSAMPLING_RATIO: *val = READ_ONCE(st->oversampling_ratio); return IIO_VAL_INT; default: return -EINVAL; } } static int max40080_write_raw(struct iio_dev *indio_dev, struct iio_chan_spec const *chan, int val, int val2, long mask) { struct max40080_state *st = iio_priv(indio_dev); guard(mutex)(&st->lock); switch (mask) { case IIO_CHAN_INFO_SCALE: /* Only the current channel has a selectable range/scale. */ if (chan->type != IIO_CURRENT) return -EINVAL; for (unsigned int i = 0; i < ARRAY_SIZE(max40080_csa_gain); i++) { if (val == st->current_scale[i][0] && val2 == st->current_scale[i][1]) return max40080_set_range(st, i); } return -EINVAL; case IIO_CHAN_INFO_OVERSAMPLING_RATIO: return max40080_set_oversampling_ratio(st, val); default: return -EINVAL; } } static int max40080_write_raw_get_fmt(struct iio_dev *indio_dev, struct iio_chan_spec const *chan, long mask) { switch (mask) { case IIO_CHAN_INFO_SCALE: return IIO_VAL_INT_PLUS_NANO; default: return IIO_VAL_INT; } } static int max40080_read_avail(struct iio_dev *indio_dev, struct iio_chan_spec const *chan, const int **vals, int *type, int *length, long info) { struct max40080_state *st = iio_priv(indio_dev); switch (info) { case IIO_CHAN_INFO_SCALE: if (chan->type != IIO_CURRENT) return -EINVAL; *vals = (int *)st->current_scale; *length = ARRAY_SIZE(max40080_csa_gain) * 2; *type = IIO_VAL_INT_PLUS_NANO; return IIO_AVAIL_LIST; case IIO_CHAN_INFO_OVERSAMPLING_RATIO: *vals = max40080_oversampling_avail; *length = ARRAY_SIZE(max40080_oversampling_avail); *type = IIO_VAL_INT; return IIO_AVAIL_LIST; default: return -EINVAL; } } static int max40080_reg_access(struct iio_dev *indio_dev, unsigned int reg, unsigned int write_val, unsigned int *read_val) { struct max40080_state *st = iio_priv(indio_dev); int val; if (read_val) { val = i2c_smbus_read_word_data(st->client, reg); if (val < 0) return val; *read_val = val; return 0; } return i2c_smbus_write_word_data(st->client, reg, write_val); } static const struct iio_info max40080_info = { .read_raw = max40080_read_raw, .write_raw = max40080_write_raw, .write_raw_get_fmt = max40080_write_raw_get_fmt, .read_avail = max40080_read_avail, .debugfs_reg_access = &max40080_reg_access, }; static const struct iio_chan_spec max40080_channels[] = { { .type = IIO_CURRENT, .indexed = 1, .channel = 0, .info_mask_separate = BIT(IIO_CHAN_INFO_RAW) | BIT(IIO_CHAN_INFO_SCALE), .info_mask_separate_available = BIT(IIO_CHAN_INFO_SCALE), .info_mask_shared_by_all = BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO), .info_mask_shared_by_all_available = BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO), }, { .type = IIO_VOLTAGE, .indexed = 1, .channel = 0, .info_mask_separate = BIT(IIO_CHAN_INFO_RAW) | BIT(IIO_CHAN_INFO_SCALE), .info_mask_shared_by_all = BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO), .info_mask_shared_by_all_available = BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO), }, }; /* * Configure the device from the cached state. The device powers up in standby * with PEC enabled (CFG POR = 0x0060), so PEC is kept enabled throughout. */ static int max40080_init(struct max40080_state *st) { u16 fifo_cfg, cfg; int ret, filter; filter = max40080_oversampling_to_filter(st->oversampling_ratio); if (filter < 0) return filter; /* * Put the device in standby before (re)configuring the FIFO: the FIFO * configuration register can only be written while the device is not * converting. */ cfg = FIELD_PREP(MAX40080_CFG_MODE_MSK, MAX40080_CFG_MODE_STDBY) | FIELD_PREP(MAX40080_CFG_PEC_EN_MSK, 1); ret = i2c_smbus_write_word_data(st->client, MAX40080_REG_CFG, cfg); if (ret) return ret; /* Store a matched current+voltage pair per conversion. */ fifo_cfg = FIELD_PREP(MAX40080_FIFO_CFG_STORE_IV_MSK, MAX40080_FIFO_CFG_STORE_IV); ret = i2c_smbus_write_word_data(st->client, MAX40080_REG_FIFO_CFG, fifo_cfg); if (ret) return ret; /* * Use single-measurement mode: the device stays idle and converts once * per SMBus Quick Command (see max40080_trigger_measurement()), so each * read returns a fresh sample rather than a queued FIFO entry. */ cfg = FIELD_PREP(MAX40080_CFG_MODE_MSK, MAX40080_CFG_MODE_SINGLE) | FIELD_PREP(MAX40080_CFG_PEC_EN_MSK, 1) | FIELD_PREP(MAX40080_CFG_RANGE_MSK, st->range) | FIELD_PREP(MAX40080_CFG_FILTER_MSK, filter); return i2c_smbus_write_word_data(st->client, MAX40080_REG_CFG, cfg); } static int max40080_probe(struct i2c_client *client) { struct device *dev = &client->dev; const char *propname; struct iio_dev *indio_dev; struct max40080_state *st; int ret; /* * The device powers up with PEC enabled (CFG POR = 0x0060) and rejects * unprotected transactions, so PEC support is mandatory, along with * word access, the I2C block read used for the current/voltage pair, * and the Quick Command used to trigger a conversion. */ if (!i2c_check_functionality(client->adapter, I2C_FUNC_SMBUS_WORD_DATA | I2C_FUNC_SMBUS_I2C_BLOCK | I2C_FUNC_SMBUS_QUICK | I2C_FUNC_SMBUS_PEC)) return -EOPNOTSUPP; client->flags |= I2C_CLIENT_PEC; indio_dev = devm_iio_device_alloc(dev, sizeof(*st)); if (!indio_dev) return -ENOMEM; st = iio_priv(indio_dev); st->client = client; ret = devm_mutex_init(dev, &st->lock); if (ret) return ret; propname = "shunt-resistor-micro-ohms"; ret = device_property_read_u32(dev, propname, &st->shunt_resistor_uOhm); if (ret) return dev_err_probe(dev, ret, "can't read %s\n", propname); if (!st->shunt_resistor_uOhm) return dev_err_probe(dev, -EINVAL, "%s must be non-zero\n", propname); max40080_calc_current_scale(st); /* Defaults: 50 mV range, no averaging. */ st->range = MAX40080_CFG_RANGE_50mV; st->oversampling_ratio = 1; indio_dev->name = "max40080"; indio_dev->info = &max40080_info; indio_dev->modes = INDIO_DIRECT_MODE; indio_dev->channels = max40080_channels; indio_dev->num_channels = ARRAY_SIZE(max40080_channels); ret = max40080_init(st); if (ret) return ret; return devm_iio_device_register(dev, indio_dev); } static const struct i2c_device_id max40080_i2c_ids[] = { { .name = "max40080" }, { } }; MODULE_DEVICE_TABLE(i2c, max40080_i2c_ids); static const struct of_device_id max40080_of_match[] = { { .compatible = "adi,max40080" }, { } }; MODULE_DEVICE_TABLE(of, max40080_of_match); static struct i2c_driver max40080_driver = { .driver = { .name = "max40080", .of_match_table = max40080_of_match, }, .probe = max40080_probe, .id_table = max40080_i2c_ids, }; module_i2c_driver(max40080_driver); MODULE_AUTHOR("Ciprian Hegbeli "); MODULE_AUTHOR("Stefan Popa "); MODULE_DESCRIPTION("Analog Devices MAX40080 current-sense amplifier driver"); MODULE_LICENSE("GPL");