/*
 * Driver for older Chrome OS EC accelerometer
 *
 * Copyright 2017 Google, Inc
 *
 * This software is licensed under the terms of the GNU General Public
 * License version 2, as published by the Free Software Foundation, and
 * may be copied, distributed, and modified under those terms.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * This driver uses the memory mapper cros-ec interface to communicate
 * with the Chrome OS EC about accelerometer data.
 * Accelerometer access is presented through iio sysfs.
 */

#include <linux/delay.h>
#include <linux/device.h>
#include <linux/iio/buffer.h>
#include <linux/iio/iio.h>
#include <linux/iio/kfifo_buf.h>
#include <linux/iio/trigger_consumer.h>
#include <linux/iio/triggered_buffer.h>
#include <linux/kernel.h>
#include <linux/mfd/cros_ec.h>
#include <linux/mfd/cros_ec_commands.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/sysfs.h>
#include <linux/platform_device.h>

#define DRV_NAME        "cros-ec-accel-legacy"

/*
 * Sensor scale hard coded at 10 bits per g, computed as:
 * g / (2^10 - 1) = 0.009586168; with g = 9.80665 m.s^-2
 */
#define ACCEL_LEGACY_NSCALE 9586168

/* Indices for EC sensor values. */
enum {
        X,
        Y,
        Z,
        MAX_AXIS,
};

/* State data for cros_ec_accel_legacy iio driver. */
struct cros_ec_accel_legacy_state {
        struct cros_ec_device *ec;

        /*
         * Array holding data from a single capture. 2 bytes per channel
         * for the 3 channels plus the timestamp which is always last and
         * 8-bytes aligned.
         */
        s16 capture_data[8];
        s8 sign[MAX_AXIS];
        u8 sensor_num;
};

static int ec_cmd_read_u8(struct cros_ec_device *ec, unsigned int offset,
                          u8 *dest)
{
        return ec->cmd_readmem(ec, offset, 1, dest);
}

static int ec_cmd_read_u16(struct cros_ec_device *ec, unsigned int offset,
                           u16 *dest)
{
        __le16 tmp;
        int ret = ec->cmd_readmem(ec, offset, 2, &tmp);

        *dest = le16_to_cpu(tmp);

        return ret;
}

/**
 * read_ec_until_not_busy() - Read from EC status byte until it reads not busy.
 * @st: Pointer to state information for device.
 *
 * This function reads EC status until its busy bit gets cleared. It does not
 * wait indefinitely and returns -EIO if the EC status is still busy after a
 * few hundreds milliseconds.
 *
 * Return: 8-bit status if ok, -EIO on error
 */
static int read_ec_until_not_busy(struct cros_ec_accel_legacy_state *st)
{
        struct cros_ec_device *ec = st->ec;
        u8 status;
        int attempts = 0;

        ec_cmd_read_u8(ec, EC_MEMMAP_ACC_STATUS, &status);
        while (status & EC_MEMMAP_ACC_STATUS_BUSY_BIT) {
                /* Give up after enough attempts, return error. */
                if (attempts++ >= 50)
                        return -EIO;

                /* Small delay every so often. */
                if (attempts % 5 == 0)
                        msleep(25);

                ec_cmd_read_u8(ec, EC_MEMMAP_ACC_STATUS, &status);
        }

        return status;
}

/**
 * read_ec_accel_data_unsafe() - Read acceleration data from EC shared memory.
 * @st:        Pointer to state information for device.
 * @scan_mask: Bitmap of the sensor indices to scan.
 * @data:      Location to store data.
 *
 * This is the unsafe function for reading the EC data. It does not guarantee
 * that the EC will not modify the data as it is being read in.
 */
static void read_ec_accel_data_unsafe(struct cros_ec_accel_legacy_state *st,
                                      unsigned long scan_mask, s16 *data)
{
        int i = 0;
        int num_enabled = bitmap_weight(&scan_mask, MAX_AXIS);

        /* Read all sensors enabled in scan_mask. Each value is 2 bytes. */
        while (num_enabled--) {
                i = find_next_bit(&scan_mask, MAX_AXIS, i);
                ec_cmd_read_u16(st->ec,
                                EC_MEMMAP_ACC_DATA +
                                sizeof(s16) *
                                (1 + i + st->sensor_num * MAX_AXIS),
                                data);
                *data *= st->sign[i];
                i++;
                data++;
        }
}

/**
 * read_ec_accel_data() - Read acceleration data from EC shared memory.
 * @st:        Pointer to state information for device.
 * @scan_mask: Bitmap of the sensor indices to scan.
 * @data:      Location to store data.
 *
 * This is the safe function for reading the EC data. It guarantees that
 * the data sampled was not modified by the EC while being read.
 *
 * Return: 0 if ok, -ve on error
 */
static int read_ec_accel_data(struct cros_ec_accel_legacy_state *st,
                              unsigned long scan_mask, s16 *data)
{
        u8 samp_id = 0xff;
        u8 status = 0;
        int ret;
        int attempts = 0;

        /*
         * Continually read all data from EC until the status byte after
         * all reads reflects that the EC is not busy and the sample id
         * matches the sample id from before all reads. This guarantees
         * that data read in was not modified by the EC while reading.
         */
        while ((status & (EC_MEMMAP_ACC_STATUS_BUSY_BIT |
                          EC_MEMMAP_ACC_STATUS_SAMPLE_ID_MASK)) != samp_id) {
                /* If we have tried to read too many times, return error. */
                if (attempts++ >= 5)
                        return -EIO;

                /* Read status byte until EC is not busy. */
                ret = read_ec_until_not_busy(st);
                if (ret < 0)
                        return ret;
                status = ret;

                /*
                 * Store the current sample id so that we can compare to the
                 * sample id after reading the data.
                 */
                samp_id = status & EC_MEMMAP_ACC_STATUS_SAMPLE_ID_MASK;

                /* Read all EC data, format it, and store it into data. */
                read_ec_accel_data_unsafe(st, scan_mask, data);

                /* Read status byte. */
                ec_cmd_read_u8(st->ec, EC_MEMMAP_ACC_STATUS, &status);
        }

        return 0;
}

static int cros_ec_accel_legacy_read(struct iio_dev *indio_dev,
                                     struct iio_chan_spec const *chan,
                                     int *val, int *val2, long mask)
{
        struct cros_ec_accel_legacy_state *st = iio_priv(indio_dev);
        s16 data = 0;
        int ret = IIO_VAL_INT;

        switch (mask) {
        case IIO_CHAN_INFO_RAW:
                ret = read_ec_accel_data(st, (1 << chan->scan_index), &data);
                if (ret)
                        return ret;
                *val = data;
                return IIO_VAL_INT;
        case IIO_CHAN_INFO_SCALE:
                *val = 0;
                *val2 = ACCEL_LEGACY_NSCALE;
                return IIO_VAL_INT_PLUS_NANO;
        case IIO_CHAN_INFO_CALIBBIAS:
                /* Calibration not supported. */
                *val = 0;
                return IIO_VAL_INT;
        default:
                return -EINVAL;
        }
}

static int cros_ec_accel_legacy_write(struct iio_dev *indio_dev,
                                      struct iio_chan_spec const *chan,
                                      int val, int val2, long mask)
{
        /*
         * Do nothing but don't return an error code to allow calibration
         * script to work.
         */
        if (mask == IIO_CHAN_INFO_CALIBBIAS)
                return 0;

        return -EINVAL;
}

static const struct iio_info cros_ec_accel_legacy_info = {
        .read_raw = &cros_ec_accel_legacy_read,
        .write_raw = &cros_ec_accel_legacy_write,
};

/**
 * cros_ec_accel_legacy_capture() - The trigger handler function
 * @irq: The interrupt number.
 * @p:   Private data - always a pointer to the poll func.
 *
 * On a trigger event occurring, if the pollfunc is attached then this
 * handler is called as a threaded interrupt (and hence may sleep). It
 * is responsible for grabbing data from the device and pushing it into
 * the associated buffer.
 *
 * Return: IRQ_HANDLED
 */
static irqreturn_t cros_ec_accel_legacy_capture(int irq, void *p)
{
        struct iio_poll_func *pf = p;
        struct iio_dev *indio_dev = pf->indio_dev;
        struct cros_ec_accel_legacy_state *st = iio_priv(indio_dev);

        /* Clear capture data. */
        memset(st->capture_data, 0, sizeof(st->capture_data));

        /*
         * Read data based on which channels are enabled in scan mask. Note
         * that on a capture we are always reading the calibrated data.
         */
        read_ec_accel_data(st, *indio_dev->active_scan_mask, st->capture_data);

        iio_push_to_buffers_with_timestamp(indio_dev, (void *)st->capture_data,
                                           iio_get_time_ns(indio_dev));

        /*
         * Tell the core we are done with this trigger and ready for the
         * next one.
         */
        iio_trigger_notify_done(indio_dev->trig);

        return IRQ_HANDLED;
}

static char *cros_ec_accel_legacy_loc_strings[] = {
        [MOTIONSENSE_LOC_BASE] = "base",
        [MOTIONSENSE_LOC_LID] = "lid",
        [MOTIONSENSE_LOC_MAX] = "unknown",
};

static ssize_t cros_ec_accel_legacy_loc(struct iio_dev *indio_dev,
                                        uintptr_t private,
                                        const struct iio_chan_spec *chan,
                                        char *buf)
{
        struct cros_ec_accel_legacy_state *st = iio_priv(indio_dev);

        return sprintf(buf, "%s\n",
                       cros_ec_accel_legacy_loc_strings[st->sensor_num +
                                                        MOTIONSENSE_LOC_BASE]);
}

static ssize_t cros_ec_accel_legacy_id(struct iio_dev *indio_dev,
                                       uintptr_t private,
                                       const struct iio_chan_spec *chan,
                                       char *buf)
{
        struct cros_ec_accel_legacy_state *st = iio_priv(indio_dev);

        return sprintf(buf, "%d\n", st->sensor_num);
}

static const struct iio_chan_spec_ext_info cros_ec_accel_legacy_ext_info[] = {
        {
                .name = "id",
                .shared = IIO_SHARED_BY_ALL,
                .read = cros_ec_accel_legacy_id,
        },
        {
                .name = "location",
                .shared = IIO_SHARED_BY_ALL,
                .read = cros_ec_accel_legacy_loc,
        },
        { }
};

#define CROS_EC_ACCEL_LEGACY_CHAN(_axis)                                \
        {                                                               \
                .type = IIO_ACCEL,                                      \
                .channel2 = IIO_MOD_X + (_axis),                        \
                .modified = 1,                                          \
                .info_mask_separate =                                   \
                        BIT(IIO_CHAN_INFO_RAW) |                        \
                        BIT(IIO_CHAN_INFO_SCALE) |                      \
                        BIT(IIO_CHAN_INFO_CALIBBIAS),                   \
                .info_mask_shared_by_all = BIT(IIO_CHAN_INFO_SCALE),    \
                .ext_info = cros_ec_accel_legacy_ext_info,              \
                .scan_type = {                                          \
                        .sign = 's',                                    \
                        .realbits = 16,                                 \
                        .storagebits = 16,                              \
                },                                                      \
        }                                                               \

static struct iio_chan_spec ec_accel_channels[] = {
        CROS_EC_ACCEL_LEGACY_CHAN(X),
        CROS_EC_ACCEL_LEGACY_CHAN(Y),
        CROS_EC_ACCEL_LEGACY_CHAN(Z),
        IIO_CHAN_SOFT_TIMESTAMP(MAX_AXIS)
};

static int cros_ec_accel_legacy_probe(struct platform_device *pdev)
{
        struct device *dev = &pdev->dev;
        struct cros_ec_dev *ec = dev_get_drvdata(dev->parent);
        struct cros_ec_sensor_platform *sensor_platform = dev_get_platdata(dev);
        struct iio_dev *indio_dev;
        struct cros_ec_accel_legacy_state *state;
        int ret, i;

        if (!ec || !ec->ec_dev) {
                dev_warn(&pdev->dev, "No EC device found.\n");
                return -EINVAL;
        }

        if (!ec->ec_dev->cmd_readmem) {
                dev_warn(&pdev->dev, "EC does not support direct reads.\n");
                return -EINVAL;
        }

        indio_dev = devm_iio_device_alloc(&pdev->dev, sizeof(*state));
        if (!indio_dev)
                return -ENOMEM;

        platform_set_drvdata(pdev, indio_dev);
        state = iio_priv(indio_dev);
        state->ec = ec->ec_dev;
        state->sensor_num = sensor_platform->sensor_num;

        indio_dev->dev.parent = dev;
        indio_dev->name = pdev->name;
        indio_dev->channels = ec_accel_channels;
        /*
         * Present the channel using HTML5 standard:
         * need to invert X and Y and invert some lid axis.
         */
        for (i = X ; i < MAX_AXIS; i++) {
                switch (i) {
                case X:
                        ec_accel_channels[X].scan_index = Y;
                case Y:
                        ec_accel_channels[Y].scan_index = X;
                case Z:
                        ec_accel_channels[Z].scan_index = Z;
                }
                if (state->sensor_num == MOTIONSENSE_LOC_LID && i != Y)
                        state->sign[i] = -1;
                else
                        state->sign[i] = 1;
        }
        indio_dev->num_channels = ARRAY_SIZE(ec_accel_channels);
        indio_dev->dev.parent = &pdev->dev;
        indio_dev->info = &cros_ec_accel_legacy_info;
        indio_dev->modes = INDIO_DIRECT_MODE;

        ret = devm_iio_triggered_buffer_setup(dev, indio_dev, NULL,
                                              cros_ec_accel_legacy_capture,
                                              NULL);
        if (ret)
                return ret;

        return devm_iio_device_register(dev, indio_dev);
}

static struct platform_driver cros_ec_accel_platform_driver = {
        .driver = {
                .name   = DRV_NAME,
        },
        .probe          = cros_ec_accel_legacy_probe,
};
module_platform_driver(cros_ec_accel_platform_driver);

MODULE_DESCRIPTION("ChromeOS EC legacy accelerometer driver");
MODULE_AUTHOR("Gwendal Grignou <gwendal@chromium.org>");
MODULE_LICENSE("GPL");
MODULE_ALIAS("platform:" DRV_NAME);