// SPDX-License-Identifier: (GPL-2.0-only)
/*
 * Analog Devices Inc. AD7625 ADC driver
 *
 * Copyright 2024 Analog Devices Inc.
 * Copyright 2024 BayLibre, SAS
 *
 * Note that this driver requires the AXI ADC IP block configured for
 * LVDS to function. See Documentation/iio/ad7625.rst for more
 * information.
 */

#include <linux/clk.h>
#include <linux/device.h>
#include <linux/err.h>
#include <linux/gpio/consumer.h>
#include <linux/iio/backend.h>
#include <linux/iio/iio.h>
#include <linux/kernel.h>
#include <linux/mod_devicetable.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/pwm.h>
#include <linux/regulator/consumer.h>
#include <linux/units.h>

#define AD7625_INTERNAL_REF_MV 4096
#define AD7960_MAX_NBW_FREQ (2 * MEGA)

struct ad7625_timing_spec {
        /* Max conversion high time (t_{CNVH}). */
        unsigned int conv_high_ns;
        /* Max conversion to MSB delay (t_{MSB}). */
        unsigned int conv_msb_ns;
};

struct ad7625_chip_info {
        const char *name;
        const unsigned int max_sample_freq_hz;
        const struct ad7625_timing_spec *timing_spec;
        const struct iio_chan_spec chan_spec;
        const bool has_power_down_state;
        const bool has_bandwidth_control;
        const bool has_internal_vref;
};

/* AD7625_CHAN_SPEC - Define a chan spec structure for a specific chip */
#define AD7625_CHAN_SPEC(_bits) {                                       \
        .type = IIO_VOLTAGE,                                            \
        .indexed = 1,                                                   \
        .differential = 1,                                              \
        .channel = 0,                                                   \
        .channel2 = 1,                                                  \
        .info_mask_separate = BIT(IIO_CHAN_INFO_SCALE),                 \
        .info_mask_shared_by_all = BIT(IIO_CHAN_INFO_SAMP_FREQ),        \
        .scan_index = 0,                                                \
        .scan_type.sign = 's',                                          \
        .scan_type.storagebits = (_bits) > 16 ? 32 : 16,                \
        .scan_type.realbits = (_bits),                                  \
}

struct ad7625_state {
        const struct ad7625_chip_info *info;
        struct iio_backend *back;
        /* rate of the clock gated by the "clk_gate" PWM */
        u32 ref_clk_rate_hz;
        /* PWM burst signal for transferring acquired data to the host */
        struct pwm_device *clk_gate_pwm;
        /*
         * PWM control signal for initiating data conversion. Analog
         * inputs are sampled beginning on this signal's rising edge.
         */
        struct pwm_device *cnv_pwm;
        /*
         * Waveforms containing the last-requested and rounded
         * properties for the clk_gate and cnv PWMs
         */
        struct pwm_waveform clk_gate_wf;
        struct pwm_waveform cnv_wf;
        unsigned int vref_mv;
        u32 sampling_freq_hz;
        /*
         * Optional GPIOs for controlling device state. EN0 and EN1
         * determine voltage reference configuration and on/off state.
         * EN2 controls the device -3dB bandwidth (and by extension, max
         * sample rate). EN3 controls the VCM reference output. EN2 and
         * EN3 are only present for the AD796x devices.
         */
        struct gpio_desc *en_gpios[4];
        bool can_power_down;
        bool can_refin;
        bool can_ref_4v096;
        /*
         * Indicate whether the bandwidth can be narrow (9MHz).
         * When true, device sample rate must also be < 2MSPS.
         */
        bool can_narrow_bandwidth;
        /* Indicate whether the bandwidth can be wide (28MHz). */
        bool can_wide_bandwidth;
        bool can_ref_5v;
        bool can_snooze;
        bool can_test_pattern;
        /* Indicate whether there is a REFIN supply connected */
        bool have_refin;
};

static const struct ad7625_timing_spec ad7625_timing_spec = {
        .conv_high_ns = 40,
        .conv_msb_ns = 145,
};

static const struct ad7625_timing_spec ad7626_timing_spec = {
        .conv_high_ns = 40,
        .conv_msb_ns = 80,
};

/*
 * conv_msb_ns is set to 0 instead of the datasheet maximum of 200ns to
 * avoid exceeding the minimum conversion time, i.e. it is effectively
 * modulo 200 and offset by a full period. Values greater than or equal
 * to the period would be rejected by the PWM API.
 */
static const struct ad7625_timing_spec ad7960_timing_spec = {
        .conv_high_ns = 80,
        .conv_msb_ns = 0,
};

static const struct ad7625_chip_info ad7625_chip_info = {
        .name = "ad7625",
        .max_sample_freq_hz = 6 * MEGA,
        .timing_spec = &ad7625_timing_spec,
        .chan_spec = AD7625_CHAN_SPEC(16),
        .has_power_down_state = false,
        .has_bandwidth_control = false,
        .has_internal_vref = true,
};

static const struct ad7625_chip_info ad7626_chip_info = {
        .name = "ad7626",
        .max_sample_freq_hz = 10 * MEGA,
        .timing_spec = &ad7626_timing_spec,
        .chan_spec = AD7625_CHAN_SPEC(16),
        .has_power_down_state = true,
        .has_bandwidth_control = false,
        .has_internal_vref = true,
};

static const struct ad7625_chip_info ad7960_chip_info = {
        .name = "ad7960",
        .max_sample_freq_hz = 5 * MEGA,
        .timing_spec = &ad7960_timing_spec,
        .chan_spec = AD7625_CHAN_SPEC(18),
        .has_power_down_state = true,
        .has_bandwidth_control = true,
        .has_internal_vref = false,
};

static const struct ad7625_chip_info ad7961_chip_info = {
        .name = "ad7961",
        .max_sample_freq_hz = 5 * MEGA,
        .timing_spec = &ad7960_timing_spec,
        .chan_spec = AD7625_CHAN_SPEC(16),
        .has_power_down_state = true,
        .has_bandwidth_control = true,
        .has_internal_vref = false,
};

enum ad7960_mode {
        AD7960_MODE_POWER_DOWN,
        AD7960_MODE_SNOOZE,
        AD7960_MODE_NARROW_BANDWIDTH,
        AD7960_MODE_WIDE_BANDWIDTH,
        AD7960_MODE_TEST_PATTERN,
};

static int ad7625_set_sampling_freq(struct ad7625_state *st, u32 freq)
{
        u32 target;
        struct pwm_waveform clk_gate_wf = { }, cnv_wf = { };
        int ret;

        target = DIV_ROUND_UP(NSEC_PER_SEC, freq);
        cnv_wf.period_length_ns = clamp(target, 100, 10 * KILO);

        /*
         * Use the maximum conversion time t_CNVH from the datasheet as
         * the duty_cycle for ref_clk, cnv, and clk_gate
         */
        cnv_wf.duty_length_ns = st->info->timing_spec->conv_high_ns;

        ret = pwm_round_waveform_might_sleep(st->cnv_pwm, &cnv_wf);
        if (ret)
                return ret;

        /*
         * Set up the burst signal for transferring data. period and
         * offset should mirror the CNV signal
         */
        clk_gate_wf.period_length_ns = cnv_wf.period_length_ns;

        clk_gate_wf.duty_length_ns = DIV_ROUND_UP_ULL((u64)NSEC_PER_SEC *
                st->info->chan_spec.scan_type.realbits,
                st->ref_clk_rate_hz);

        /* max t_MSB from datasheet */
        clk_gate_wf.duty_offset_ns = st->info->timing_spec->conv_msb_ns;

        ret = pwm_round_waveform_might_sleep(st->clk_gate_pwm, &clk_gate_wf);
        if (ret)
                return ret;

        st->cnv_wf = cnv_wf;
        st->clk_gate_wf = clk_gate_wf;

        /* TODO: Add a rounding API for PWMs that can simplify this */
        target = DIV_ROUND_CLOSEST(st->ref_clk_rate_hz, freq);
        st->sampling_freq_hz = DIV_ROUND_CLOSEST(st->ref_clk_rate_hz,
                                                 target);

        return 0;
}

static int ad7625_read_raw(struct iio_dev *indio_dev,
                           const struct iio_chan_spec *chan,
                           int *val, int *val2, long info)
{
        struct ad7625_state *st = iio_priv(indio_dev);

        switch (info) {
        case IIO_CHAN_INFO_SAMP_FREQ:
                *val = st->sampling_freq_hz;

                return IIO_VAL_INT;

        case IIO_CHAN_INFO_SCALE:
                *val = st->vref_mv;
                *val2 = chan->scan_type.realbits - 1;

                return IIO_VAL_FRACTIONAL_LOG2;

        default:
                return -EINVAL;
        }
}

static int ad7625_write_raw(struct iio_dev *indio_dev,
                            struct iio_chan_spec const *chan,
                            int val, int val2, long info)
{
        struct ad7625_state *st = iio_priv(indio_dev);
        int ret;

        switch (info) {
        case IIO_CHAN_INFO_SAMP_FREQ:
                if (!iio_device_claim_direct(indio_dev))
                        return -EBUSY;
                ret = ad7625_set_sampling_freq(st, val);
                iio_device_release_direct(indio_dev);
                return ret;
        default:
                return -EINVAL;
        }
}

static int ad7625_parse_mode(struct device *dev, struct ad7625_state *st,
                             int num_gpios)
{
        bool en_always_on[4], en_always_off[4];
        bool en_may_be_on[4], en_may_be_off[4];
        char en_gpio_buf[4];
        char always_on_buf[18];
        int i;

        for (i = 0; i < num_gpios; i++) {
                snprintf(en_gpio_buf, sizeof(en_gpio_buf), "en%d", i);
                snprintf(always_on_buf, sizeof(always_on_buf),
                         "adi,en%d-always-on", i);
                /* Set the device to 0b0000 (power-down mode) by default */
                st->en_gpios[i] = devm_gpiod_get_optional(dev, en_gpio_buf,
                                                          GPIOD_OUT_LOW);
                if (IS_ERR(st->en_gpios[i]))
                        return dev_err_probe(dev, PTR_ERR(st->en_gpios[i]),
                                             "failed to get EN%d GPIO\n", i);

                en_always_on[i] = device_property_read_bool(dev, always_on_buf);
                if (st->en_gpios[i] && en_always_on[i])
                        return dev_err_probe(dev, -EINVAL,
                                "cannot have adi,en%d-always-on and en%d-gpios\n", i, i);

                en_may_be_off[i] = !en_always_on[i];
                en_may_be_on[i] = en_always_on[i] || st->en_gpios[i];
                en_always_off[i] = !en_always_on[i] && !st->en_gpios[i];
        }

        /*
         * Power down is mode 0bXX00, but not all devices have a valid
         * power down state.
         */
        st->can_power_down = en_may_be_off[1] && en_may_be_off[0] &&
                             st->info->has_power_down_state;
        /*
         * The REFIN pin can take a 1.2V (AD762x) or 2.048V (AD796x)
         * external reference when the mode is 0bXX01.
         */
        st->can_refin = en_may_be_off[1] && en_may_be_on[0];
        /* 4.096V can be applied to REF when the EN mode is 0bXX10. */
        st->can_ref_4v096 = en_may_be_on[1] && en_may_be_off[0];

        /* Avoid AD796x-specific setup if the part is an AD762x */
        if (num_gpios == 2)
                return 0;

        /* mode 0b1100 (AD796x) is invalid */
        if (en_always_on[3] && en_always_on[2] &&
            en_always_off[1] && en_always_off[0])
                return dev_err_probe(dev, -EINVAL,
                                     "EN GPIOs set to invalid mode 0b1100\n");
        /*
         * 5V can be applied to the AD796x REF pin when the EN mode is
         * the same (0bX001 or 0bX101) as for can_refin, and REFIN is
         * 0V.
         */
        st->can_ref_5v = st->can_refin;
        /*
         * Bandwidth (AD796x) is controlled solely by EN2. If it's
         * specified and not hard-wired, then we can configure it to
         * change the bandwidth between 28MHz and 9MHz.
         */
        st->can_narrow_bandwidth = en_may_be_on[2];
        /* Wide bandwidth mode is possible if EN2 can be 0. */
        st->can_wide_bandwidth = en_may_be_off[2];
        /* Snooze mode (AD796x) is 0bXX11 when REFIN = 0V. */
        st->can_snooze = en_may_be_on[1] && en_may_be_on[0];
        /* Test pattern mode (AD796x) is 0b0100. */
        st->can_test_pattern = en_may_be_off[3] && en_may_be_on[2] &&
                               en_may_be_off[1] && en_may_be_off[0];

        return 0;
}

/* Set EN1 and EN0 based on reference voltage source */
static void ad7625_set_en_gpios_for_vref(struct ad7625_state *st,
                                         bool have_refin, int ref_mv)
{
        if (have_refin || ref_mv == 5000) {
                gpiod_set_value_cansleep(st->en_gpios[1], 0);
                gpiod_set_value_cansleep(st->en_gpios[0], 1);
        } else if (ref_mv == 4096) {
                gpiod_set_value_cansleep(st->en_gpios[1], 1);
                gpiod_set_value_cansleep(st->en_gpios[0], 0);
        } else {
                /*
                 * Unreachable by AD796x, since the driver will error if
                 * neither REF nor REFIN is provided
                 */
                gpiod_set_value_cansleep(st->en_gpios[1], 1);
                gpiod_set_value_cansleep(st->en_gpios[0], 1);
        }
}

static int ad7960_set_mode(struct ad7625_state *st, enum ad7960_mode mode,
                           bool have_refin, int ref_mv)
{
        switch (mode) {
        case AD7960_MODE_POWER_DOWN:
                if (!st->can_power_down)
                        return -EINVAL;

                gpiod_set_value_cansleep(st->en_gpios[2], 0);
                gpiod_set_value_cansleep(st->en_gpios[1], 0);
                gpiod_set_value_cansleep(st->en_gpios[0], 0);

                return 0;

        case AD7960_MODE_SNOOZE:
                if (!st->can_snooze)
                        return -EINVAL;

                gpiod_set_value_cansleep(st->en_gpios[1], 1);
                gpiod_set_value_cansleep(st->en_gpios[0], 1);

                return 0;

        case AD7960_MODE_NARROW_BANDWIDTH:
                if (!st->can_narrow_bandwidth)
                        return -EINVAL;

                gpiod_set_value_cansleep(st->en_gpios[2], 1);
                ad7625_set_en_gpios_for_vref(st, have_refin, ref_mv);

                return 0;

        case AD7960_MODE_WIDE_BANDWIDTH:
                if (!st->can_wide_bandwidth)
                        return -EINVAL;

                gpiod_set_value_cansleep(st->en_gpios[2], 0);
                ad7625_set_en_gpios_for_vref(st, have_refin, ref_mv);

                return 0;

        case AD7960_MODE_TEST_PATTERN:
                if (!st->can_test_pattern)
                        return -EINVAL;

                gpiod_set_value_cansleep(st->en_gpios[3], 0);
                gpiod_set_value_cansleep(st->en_gpios[2], 1);
                gpiod_set_value_cansleep(st->en_gpios[1], 0);
                gpiod_set_value_cansleep(st->en_gpios[0], 0);

                return 0;

        default:
                return -EINVAL;
        }
}

static int ad7625_buffer_preenable(struct iio_dev *indio_dev)
{
        struct ad7625_state *st = iio_priv(indio_dev);
        int ret;

        ret = pwm_set_waveform_might_sleep(st->cnv_pwm, &st->cnv_wf, false);
        if (ret)
                return ret;

        ret = pwm_set_waveform_might_sleep(st->clk_gate_pwm,
                                           &st->clk_gate_wf, false);
        if (ret) {
                /* Disable cnv PWM if clk_gate setup failed */
                pwm_disable(st->cnv_pwm);
                return ret;
        }

        return 0;
}

static int ad7625_buffer_postdisable(struct iio_dev *indio_dev)
{
        struct ad7625_state *st = iio_priv(indio_dev);

        pwm_disable(st->clk_gate_pwm);
        pwm_disable(st->cnv_pwm);

        return 0;
}

static const struct iio_info ad7625_info = {
        .read_raw = ad7625_read_raw,
        .write_raw = ad7625_write_raw,
};

static const struct iio_buffer_setup_ops ad7625_buffer_setup_ops = {
        .preenable = &ad7625_buffer_preenable,
        .postdisable = &ad7625_buffer_postdisable,
};

static int devm_ad7625_pwm_get(struct device *dev,
                               struct ad7625_state *st)
{
        struct clk *ref_clk;
        u32 ref_clk_rate_hz;

        st->cnv_pwm = devm_pwm_get(dev, "cnv");
        if (IS_ERR(st->cnv_pwm))
                return dev_err_probe(dev, PTR_ERR(st->cnv_pwm),
                                     "failed to get cnv pwm\n");

        /* Preemptively disable the PWM in case it was enabled at boot */
        pwm_disable(st->cnv_pwm);

        st->clk_gate_pwm = devm_pwm_get(dev, "clk_gate");
        if (IS_ERR(st->clk_gate_pwm))
                return dev_err_probe(dev, PTR_ERR(st->clk_gate_pwm),
                                     "failed to get clk_gate pwm\n");

        /* Preemptively disable the PWM in case it was enabled at boot */
        pwm_disable(st->clk_gate_pwm);

        ref_clk = devm_clk_get_enabled(dev, NULL);
        if (IS_ERR(ref_clk))
                return dev_err_probe(dev, PTR_ERR(ref_clk),
                                     "failed to get ref_clk\n");

        ref_clk_rate_hz = clk_get_rate(ref_clk);
        if (!ref_clk_rate_hz)
                return dev_err_probe(dev, -EINVAL,
                                     "failed to get ref_clk rate\n");

        st->ref_clk_rate_hz = ref_clk_rate_hz;

        return 0;
}

/*
 * There are three required input voltages for each device, plus two
 * conditionally-optional (depending on part) REF and REFIN voltages
 * where their validity depends upon the EN pin configuration.
 *
 * Power-up info for the device says to bring up vio, then vdd2, then
 * vdd1, so list them in that order in the regulator_names array.
 *
 * The reference voltage source is determined like so:
 * - internal reference: neither REF or REFIN is connected (invalid for
 *   AD796x)
 * - internal buffer, external reference: REF not connected, REFIN
 *   connected
 * - external reference: REF connected, REFIN not connected
 */
static int devm_ad7625_regulator_setup(struct device *dev,
                                       struct ad7625_state *st)
{
        static const char * const regulator_names[] = { "vio", "vdd2", "vdd1" };
        int ret, ref_mv;

        ret = devm_regulator_bulk_get_enable(dev, ARRAY_SIZE(regulator_names),
                                             regulator_names);
        if (ret)
                return ret;

        ret = devm_regulator_get_enable_read_voltage(dev, "ref");
        if (ret < 0 && ret != -ENODEV)
                return dev_err_probe(dev, ret, "failed to get REF voltage\n");

        ref_mv = ret == -ENODEV ? 0 : ret / 1000;

        ret = devm_regulator_get_enable_optional(dev, "refin");
        if (ret < 0 && ret != -ENODEV)
                return dev_err_probe(dev, ret, "failed to get REFIN voltage\n");

        st->have_refin = ret != -ENODEV;

        if (st->have_refin && !st->can_refin)
                return dev_err_probe(dev, -EINVAL,
                                     "REFIN provided in unsupported mode\n");

        if (!st->info->has_internal_vref && !st->have_refin && !ref_mv)
                return dev_err_probe(dev, -EINVAL,
                                     "Need either REFIN or REF\n");

        if (st->have_refin && ref_mv)
                return dev_err_probe(dev, -EINVAL,
                                     "cannot have both REFIN and REF supplies\n");

        if (ref_mv == 4096 && !st->can_ref_4v096)
                return dev_err_probe(dev, -EINVAL,
                                     "REF is 4.096V in unsupported mode\n");

        if (ref_mv == 5000 && !st->can_ref_5v)
                return dev_err_probe(dev, -EINVAL,
                                     "REF is 5V in unsupported mode\n");

        st->vref_mv = ref_mv ?: AD7625_INTERNAL_REF_MV;

        return 0;
}

static int ad7625_probe(struct platform_device *pdev)
{
        struct device *dev = &pdev->dev;
        struct iio_dev *indio_dev;
        struct ad7625_state *st;
        int ret;
        u32 default_sample_freq;

        indio_dev = devm_iio_device_alloc(dev, sizeof(*st));
        if (!indio_dev)
                return -ENOMEM;

        st = iio_priv(indio_dev);

        st->info = device_get_match_data(dev);
        if (!st->info)
                return dev_err_probe(dev, -EINVAL, "no chip info\n");

        if (device_property_read_bool(dev, "adi,no-dco"))
                return dev_err_probe(dev, -EINVAL,
                                     "self-clocked mode not supported\n");

        if (st->info->has_bandwidth_control)
                ret = ad7625_parse_mode(dev, st, 4);
        else
                ret = ad7625_parse_mode(dev, st, 2);

        if (ret)
                return ret;

        ret = devm_ad7625_regulator_setup(dev, st);
        if (ret)
                return ret;

        /* Set the device mode based on detected EN configuration. */
        if (!st->info->has_bandwidth_control) {
                ad7625_set_en_gpios_for_vref(st, st->have_refin, st->vref_mv);
        } else {
                /*
                 * If neither sampling mode is available, then report an error,
                 * since the other modes are not useful defaults.
                 */
                if (st->can_wide_bandwidth) {
                        ret = ad7960_set_mode(st, AD7960_MODE_WIDE_BANDWIDTH,
                                              st->have_refin, st->vref_mv);
                } else if (st->can_narrow_bandwidth) {
                        ret = ad7960_set_mode(st, AD7960_MODE_NARROW_BANDWIDTH,
                                              st->have_refin, st->vref_mv);
                } else {
                        return dev_err_probe(dev, -EINVAL,
                                "couldn't set device to wide or narrow bandwidth modes\n");
                }

                if (ret)
                        return dev_err_probe(dev, -EINVAL,
                                             "failed to set EN pins\n");
        }

        ret = devm_ad7625_pwm_get(dev, st);
        if (ret)
                return ret;

        indio_dev->channels = &st->info->chan_spec;
        indio_dev->num_channels = 1;
        indio_dev->name = st->info->name;
        indio_dev->info = &ad7625_info;
        indio_dev->setup_ops = &ad7625_buffer_setup_ops;

        st->back = devm_iio_backend_get(dev, NULL);
        if (IS_ERR(st->back))
                return dev_err_probe(dev, PTR_ERR(st->back),
                                     "failed to get IIO backend\n");

        ret = devm_iio_backend_request_buffer(dev, st->back, indio_dev);
        if (ret)
                return ret;

        ret = devm_iio_backend_enable(dev, st->back);
        if (ret)
                return ret;

        /*
         * Set the initial sampling frequency to the maximum, unless the
         * AD796x device is limited to narrow bandwidth by EN2 == 1, in
         * which case the sampling frequency should be limited to 2MSPS
         */
        default_sample_freq = st->info->max_sample_freq_hz;
        if (st->info->has_bandwidth_control && !st->can_wide_bandwidth)
                default_sample_freq = AD7960_MAX_NBW_FREQ;

        ret = ad7625_set_sampling_freq(st, default_sample_freq);
        if (ret)
                dev_err_probe(dev, ret,
                              "failed to set valid sampling frequency\n");

        return devm_iio_device_register(dev, indio_dev);
}

static const struct of_device_id ad7625_of_match[] = {
        { .compatible = "adi,ad7625", .data = &ad7625_chip_info },
        { .compatible = "adi,ad7626", .data = &ad7626_chip_info },
        { .compatible = "adi,ad7960", .data = &ad7960_chip_info },
        { .compatible = "adi,ad7961", .data = &ad7961_chip_info },
        { }
};
MODULE_DEVICE_TABLE(of, ad7625_of_match);

static const struct platform_device_id ad7625_device_ids[] = {
        { .name = "ad7625", .driver_data = (kernel_ulong_t)&ad7625_chip_info },
        { .name = "ad7626", .driver_data = (kernel_ulong_t)&ad7626_chip_info },
        { .name = "ad7960", .driver_data = (kernel_ulong_t)&ad7960_chip_info },
        { .name = "ad7961", .driver_data = (kernel_ulong_t)&ad7961_chip_info },
        { }
};
MODULE_DEVICE_TABLE(platform, ad7625_device_ids);

static struct platform_driver ad7625_driver = {
        .probe = ad7625_probe,
        .driver = {
                .name = "ad7625",
                .of_match_table = ad7625_of_match,
        },
        .id_table = ad7625_device_ids,
};
module_platform_driver(ad7625_driver);

MODULE_AUTHOR("Trevor Gamblin <tgamblin@baylibre.com>");
MODULE_DESCRIPTION("Analog Devices AD7625 ADC");
MODULE_LICENSE("GPL");
MODULE_IMPORT_NS("IIO_BACKEND");