// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2015-2017 Pengutronix, Uwe Kleine-König <kernel@pengutronix.de>
 */
#include <linux/kernel.h>
#include <linux/device.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/sysfs.h>

#include "siox.h"

/*
 * The lowest bit in the SIOX status word signals if the in-device watchdog is
 * ok. If the bit is set, the device is functional.
 *
 * On writing the watchdog timer is reset when this bit toggles.
 */
#define SIOX_STATUS_WDG                 0x01

/*
 * Bits 1 to 3 of the status word read as the bitwise negation of what was
 * clocked in before. The value clocked in is changed in each cycle and so
 * allows to detect transmit/receive problems.
 */
#define SIOX_STATUS_COUNTER             0x0e

/*
 * Each Siox-Device has a 4 bit type number that is neither 0 nor 15. This is
 * available in the upper nibble of the read status.
 *
 * On write these bits are DC.
 */
#define SIOX_STATUS_TYPE                0xf0

#define CREATE_TRACE_POINTS
#include <trace/events/siox.h>

static bool siox_is_registered;

static void siox_master_lock(struct siox_master *smaster)
{
        mutex_lock(&smaster->lock);
}

static void siox_master_unlock(struct siox_master *smaster)
{
        mutex_unlock(&smaster->lock);
}

static inline u8 siox_status_clean(u8 status_read, u8 status_written)
{
        /*
         * bits 3:1 of status sample the respective bit in the status
         * byte written in the previous cycle but inverted. So if you wrote the
         * status word as 0xa before (counter = 0b101), it is expected to get
         * back the counter bits as 0b010.
         *
         * So given the last status written this function toggles the there
         * unset counter bits in the read value such that the counter bits in
         * the return value are all zero iff the bits were read as expected to
         * simplify error detection.
         */

        return status_read ^ (~status_written & 0xe);
}

static bool siox_device_counter_error(struct siox_device *sdevice,
                                      u8 status_clean)
{
        return (status_clean & SIOX_STATUS_COUNTER) != 0;
}

static bool siox_device_type_error(struct siox_device *sdevice, u8 status_clean)
{
        u8 statustype = (status_clean & SIOX_STATUS_TYPE) >> 4;

        /*
         * If the device knows which value the type bits should have, check
         * against this value otherwise just rule out the invalid values 0b0000
         * and 0b1111.
         */
        if (sdevice->statustype) {
                if (statustype != sdevice->statustype)
                        return true;
        } else {
                switch (statustype) {
                case 0:
                case 0xf:
                        return true;
                }
        }

        return false;
}

static bool siox_device_wdg_error(struct siox_device *sdevice, u8 status_clean)
{
        return (status_clean & SIOX_STATUS_WDG) == 0;
}

/*
 * If there is a type or counter error the device is called "unsynced".
 */
bool siox_device_synced(struct siox_device *sdevice)
{
        if (siox_device_type_error(sdevice, sdevice->status_read_clean))
                return false;

        return !siox_device_counter_error(sdevice, sdevice->status_read_clean);

}
EXPORT_SYMBOL_GPL(siox_device_synced);

/*
 * A device is called "connected" if it is synced and the watchdog is not
 * asserted.
 */
bool siox_device_connected(struct siox_device *sdevice)
{
        if (!siox_device_synced(sdevice))
                return false;

        return !siox_device_wdg_error(sdevice, sdevice->status_read_clean);
}
EXPORT_SYMBOL_GPL(siox_device_connected);

static void siox_poll(struct siox_master *smaster)
{
        struct siox_device *sdevice;
        size_t i = smaster->setbuf_len;
        unsigned int devno = 0;
        int unsync_error = 0;

        smaster->last_poll = jiffies;

        /*
         * The counter bits change in each second cycle, the watchdog bit
         * toggles each time.
         * The counter bits hold values from [0, 6]. 7 would be possible
         * theoretically but the protocol designer considered that a bad idea
         * for reasons unknown today. (Maybe that's because then the status read
         * back has only zeros in the counter bits then which might be confused
         * with a stuck-at-0 error. But for the same reason (with s/0/1/) 0
         * could be skipped.)
         */
        if (++smaster->status > 0x0d)
                smaster->status = 0;

        memset(smaster->buf, 0, smaster->setbuf_len);

        /* prepare data pushed out to devices in buf[0..setbuf_len) */
        list_for_each_entry(sdevice, &smaster->devices, node) {
                struct siox_driver *sdriver =
                        to_siox_driver(sdevice->dev.driver);
                sdevice->status_written = smaster->status;

                i -= sdevice->inbytes;

                /*
                 * If the device or a previous one is unsynced, don't pet the
                 * watchdog. This is done to ensure that the device is kept in
                 * reset when something is wrong.
                 */
                if (!siox_device_synced(sdevice))
                        unsync_error = 1;

                if (sdriver && !unsync_error)
                        sdriver->set_data(sdevice, sdevice->status_written,
                                          &smaster->buf[i + 1]);
                else
                        /*
                         * Don't trigger watchdog if there is no driver or a
                         * sync problem
                         */
                        sdevice->status_written &= ~SIOX_STATUS_WDG;

                smaster->buf[i] = sdevice->status_written;

                trace_siox_set_data(smaster, sdevice, devno, i);

                devno++;
        }

        smaster->pushpull(smaster, smaster->setbuf_len, smaster->buf,
                          smaster->getbuf_len,
                          smaster->buf + smaster->setbuf_len);

        unsync_error = 0;

        /* interpret data pulled in from devices in buf[setbuf_len..] */
        devno = 0;
        i = smaster->setbuf_len;
        list_for_each_entry(sdevice, &smaster->devices, node) {
                struct siox_driver *sdriver =
                        to_siox_driver(sdevice->dev.driver);
                u8 status = smaster->buf[i + sdevice->outbytes - 1];
                u8 status_clean;
                u8 prev_status_clean = sdevice->status_read_clean;
                bool synced = true;
                bool connected = true;

                if (!siox_device_synced(sdevice))
                        unsync_error = 1;

                /*
                 * If the watchdog bit wasn't toggled in this cycle, report the
                 * watchdog as active to give a consistent view for drivers and
                 * sysfs consumers.
                 */
                if (!sdriver || unsync_error)
                        status &= ~SIOX_STATUS_WDG;

                status_clean =
                        siox_status_clean(status,
                                          sdevice->status_written_lastcycle);

                /* Check counter and type bits */
                if (siox_device_counter_error(sdevice, status_clean) ||
                    siox_device_type_error(sdevice, status_clean)) {
                        bool prev_error;

                        synced = false;

                        /* only report a new error if the last cycle was ok */
                        prev_error =
                                siox_device_counter_error(sdevice,
                                                          prev_status_clean) ||
                                siox_device_type_error(sdevice,
                                                       prev_status_clean);

                        if (!prev_error) {
                                sdevice->status_errors++;
                                sysfs_notify_dirent(sdevice->status_errors_kn);
                        }
                }

                /* If the device is unsynced report the watchdog as active */
                if (!synced) {
                        status &= ~SIOX_STATUS_WDG;
                        status_clean &= ~SIOX_STATUS_WDG;
                }

                if (siox_device_wdg_error(sdevice, status_clean))
                        connected = false;

                /* The watchdog state changed just now */
                if ((status_clean ^ prev_status_clean) & SIOX_STATUS_WDG) {
                        sysfs_notify_dirent(sdevice->watchdog_kn);

                        if (siox_device_wdg_error(sdevice, status_clean)) {
                                struct kernfs_node *wd_errs =
                                        sdevice->watchdog_errors_kn;

                                sdevice->watchdog_errors++;
                                sysfs_notify_dirent(wd_errs);
                        }
                }

                if (connected != sdevice->connected)
                        sysfs_notify_dirent(sdevice->connected_kn);

                sdevice->status_read_clean = status_clean;
                sdevice->status_written_lastcycle = sdevice->status_written;
                sdevice->connected = connected;

                trace_siox_get_data(smaster, sdevice, devno, status_clean, i);

                /* only give data read to driver if the device is connected */
                if (sdriver && connected)
                        sdriver->get_data(sdevice, &smaster->buf[i]);

                devno++;
                i += sdevice->outbytes;
        }
}

static int siox_poll_thread(void *data)
{
        struct siox_master *smaster = data;
        signed long timeout = 0;

        get_device(&smaster->dev);

        for (;;) {
                if (kthread_should_stop()) {
                        put_device(&smaster->dev);
                        return 0;
                }

                siox_master_lock(smaster);

                if (smaster->active) {
                        unsigned long next_poll =
                                smaster->last_poll + smaster->poll_interval;
                        if (time_is_before_eq_jiffies(next_poll))
                                siox_poll(smaster);

                        timeout = smaster->poll_interval -
                                (jiffies - smaster->last_poll);
                } else {
                        timeout = MAX_SCHEDULE_TIMEOUT;
                }

                /*
                 * Set the task to idle while holding the lock. This makes sure
                 * that we don't sleep too long when the bus is reenabled before
                 * schedule_timeout is reached.
                 */
                if (timeout > 0)
                        set_current_state(TASK_IDLE);

                siox_master_unlock(smaster);

                if (timeout > 0)
                        schedule_timeout(timeout);

                /*
                 * I'm not clear if/why it is important to set the state to
                 * RUNNING again, but it fixes a "do not call blocking ops when
                 * !TASK_RUNNING;"-warning.
                 */
                set_current_state(TASK_RUNNING);
        }
}

static int __siox_start(struct siox_master *smaster)
{
        if (!(smaster->setbuf_len + smaster->getbuf_len))
                return -ENODEV;

        if (!smaster->buf)
                return -ENOMEM;

        if (smaster->active)
                return 0;

        smaster->active = 1;
        wake_up_process(smaster->poll_thread);

        return 1;
}

static int siox_start(struct siox_master *smaster)
{
        int ret;

        siox_master_lock(smaster);
        ret = __siox_start(smaster);
        siox_master_unlock(smaster);

        return ret;
}

static int __siox_stop(struct siox_master *smaster)
{
        if (smaster->active) {
                struct siox_device *sdevice;

                smaster->active = 0;

                list_for_each_entry(sdevice, &smaster->devices, node) {
                        if (sdevice->connected)
                                sysfs_notify_dirent(sdevice->connected_kn);
                        sdevice->connected = false;
                }

                return 1;
        }
        return 0;
}

static int siox_stop(struct siox_master *smaster)
{
        int ret;

        siox_master_lock(smaster);
        ret = __siox_stop(smaster);
        siox_master_unlock(smaster);

        return ret;
}

static ssize_t type_show(struct device *dev,
                         struct device_attribute *attr, char *buf)
{
        struct siox_device *sdev = to_siox_device(dev);

        return sprintf(buf, "%s\n", sdev->type);
}

static DEVICE_ATTR_RO(type);

static ssize_t inbytes_show(struct device *dev,
                            struct device_attribute *attr, char *buf)
{
        struct siox_device *sdev = to_siox_device(dev);

        return sprintf(buf, "%zu\n", sdev->inbytes);
}

static DEVICE_ATTR_RO(inbytes);

static ssize_t outbytes_show(struct device *dev,
                             struct device_attribute *attr, char *buf)
{
        struct siox_device *sdev = to_siox_device(dev);

        return sprintf(buf, "%zu\n", sdev->outbytes);
}

static DEVICE_ATTR_RO(outbytes);

static ssize_t status_errors_show(struct device *dev,
                                  struct device_attribute *attr, char *buf)
{
        struct siox_device *sdev = to_siox_device(dev);
        unsigned int status_errors;

        siox_master_lock(sdev->smaster);

        status_errors = sdev->status_errors;

        siox_master_unlock(sdev->smaster);

        return sprintf(buf, "%u\n", status_errors);
}

static DEVICE_ATTR_RO(status_errors);

static ssize_t connected_show(struct device *dev,
                              struct device_attribute *attr, char *buf)
{
        struct siox_device *sdev = to_siox_device(dev);
        bool connected;

        siox_master_lock(sdev->smaster);

        connected = sdev->connected;

        siox_master_unlock(sdev->smaster);

        return sprintf(buf, "%u\n", connected);
}

static DEVICE_ATTR_RO(connected);

static ssize_t watchdog_show(struct device *dev,
                             struct device_attribute *attr, char *buf)
{
        struct siox_device *sdev = to_siox_device(dev);
        u8 status;

        siox_master_lock(sdev->smaster);

        status = sdev->status_read_clean;

        siox_master_unlock(sdev->smaster);

        return sprintf(buf, "%d\n", status & SIOX_STATUS_WDG);
}

static DEVICE_ATTR_RO(watchdog);

static ssize_t watchdog_errors_show(struct device *dev,
                                    struct device_attribute *attr, char *buf)
{
        struct siox_device *sdev = to_siox_device(dev);
        unsigned int watchdog_errors;

        siox_master_lock(sdev->smaster);

        watchdog_errors = sdev->watchdog_errors;

        siox_master_unlock(sdev->smaster);

        return sprintf(buf, "%u\n", watchdog_errors);
}

static DEVICE_ATTR_RO(watchdog_errors);

static struct attribute *siox_device_attrs[] = {
        &dev_attr_type.attr,
        &dev_attr_inbytes.attr,
        &dev_attr_outbytes.attr,
        &dev_attr_status_errors.attr,
        &dev_attr_connected.attr,
        &dev_attr_watchdog.attr,
        &dev_attr_watchdog_errors.attr,
        NULL
};
ATTRIBUTE_GROUPS(siox_device);

static void siox_device_release(struct device *dev)
{
        struct siox_device *sdevice = to_siox_device(dev);

        kfree(sdevice);
}

static const struct device_type siox_device_type = {
        .groups = siox_device_groups,
        .release = siox_device_release,
};

static int siox_match(struct device *dev, const struct device_driver *drv)
{
        if (dev->type != &siox_device_type)
                return 0;

        /* up to now there is only a single driver so keeping this simple */
        return 1;
}

static int siox_probe(struct device *dev)
{
        struct siox_driver *sdriver = to_siox_driver(dev->driver);
        struct siox_device *sdevice = to_siox_device(dev);

        return sdriver->probe(sdevice);
}

static void siox_remove(struct device *dev)
{
        struct siox_driver *sdriver =
                container_of(dev->driver, struct siox_driver, driver);
        struct siox_device *sdevice = to_siox_device(dev);

        if (sdriver->remove)
                sdriver->remove(sdevice);
}

static void siox_shutdown(struct device *dev)
{
        struct siox_device *sdevice = to_siox_device(dev);
        struct siox_driver *sdriver;

        if (!dev->driver)
                return;

        sdriver = container_of(dev->driver, struct siox_driver, driver);
        if (sdriver->shutdown)
                sdriver->shutdown(sdevice);
}

static const struct bus_type siox_bus_type = {
        .name = "siox",
        .match = siox_match,
        .probe = siox_probe,
        .remove = siox_remove,
        .shutdown = siox_shutdown,
};

static ssize_t active_show(struct device *dev,
                           struct device_attribute *attr, char *buf)
{
        struct siox_master *smaster = to_siox_master(dev);

        return sprintf(buf, "%d\n", smaster->active);
}

static ssize_t active_store(struct device *dev,
                            struct device_attribute *attr,
                            const char *buf, size_t count)
{
        struct siox_master *smaster = to_siox_master(dev);
        int ret;
        int active;

        ret = kstrtoint(buf, 0, &active);
        if (ret < 0)
                return ret;

        if (active)
                ret = siox_start(smaster);
        else
                ret = siox_stop(smaster);

        if (ret < 0)
                return ret;

        return count;
}

static DEVICE_ATTR_RW(active);

static struct siox_device *siox_device_add(struct siox_master *smaster,
                                           const char *type, size_t inbytes,
                                           size_t outbytes, u8 statustype);

static ssize_t device_add_store(struct device *dev,
                                struct device_attribute *attr,
                                const char *buf, size_t count)
{
        struct siox_master *smaster = to_siox_master(dev);
        int ret;
        char type[20] = "";
        size_t inbytes = 0, outbytes = 0;
        u8 statustype = 0;

        ret = sscanf(buf, "%19s %zu %zu %hhu", type, &inbytes,
                     &outbytes, &statustype);
        if (ret != 3 && ret != 4)
                return -EINVAL;

        if (strcmp(type, "siox-12x8") || inbytes != 2 || outbytes != 4)
                return -EINVAL;

        siox_device_add(smaster, "siox-12x8", inbytes, outbytes, statustype);

        return count;
}

static DEVICE_ATTR_WO(device_add);

static void siox_device_remove(struct siox_master *smaster);

static ssize_t device_remove_store(struct device *dev,
                                   struct device_attribute *attr,
                                   const char *buf, size_t count)
{
        struct siox_master *smaster = to_siox_master(dev);

        /* XXX? require to write <type> <inbytes> <outbytes> */
        siox_device_remove(smaster);

        return count;
}

static DEVICE_ATTR_WO(device_remove);

static ssize_t poll_interval_ns_show(struct device *dev,
                                     struct device_attribute *attr, char *buf)
{
        struct siox_master *smaster = to_siox_master(dev);

        return sprintf(buf, "%lld\n", jiffies_to_nsecs(smaster->poll_interval));
}

static ssize_t poll_interval_ns_store(struct device *dev,
                                      struct device_attribute *attr,
                                      const char *buf, size_t count)
{
        struct siox_master *smaster = to_siox_master(dev);
        int ret;
        u64 val;

        ret = kstrtou64(buf, 0, &val);
        if (ret < 0)
                return ret;

        siox_master_lock(smaster);

        smaster->poll_interval = nsecs_to_jiffies(val);

        siox_master_unlock(smaster);

        return count;
}

static DEVICE_ATTR_RW(poll_interval_ns);

static struct attribute *siox_master_attrs[] = {
        &dev_attr_active.attr,
        &dev_attr_device_add.attr,
        &dev_attr_device_remove.attr,
        &dev_attr_poll_interval_ns.attr,
        NULL
};
ATTRIBUTE_GROUPS(siox_master);

static void siox_master_release(struct device *dev)
{
        struct siox_master *smaster = to_siox_master(dev);

        kfree(smaster);
}

static const struct device_type siox_master_type = {
        .groups = siox_master_groups,
        .release = siox_master_release,
};

struct siox_master *siox_master_alloc(struct device *dev,
                                      size_t size)
{
        struct siox_master *smaster;

        if (!dev)
                return NULL;

        smaster = kzalloc(sizeof(*smaster) + size, GFP_KERNEL);
        if (!smaster)
                return NULL;

        device_initialize(&smaster->dev);

        smaster->busno = -1;
        smaster->dev.bus = &siox_bus_type;
        smaster->dev.type = &siox_master_type;
        smaster->dev.parent = dev;
        smaster->poll_interval = DIV_ROUND_UP(HZ, 40);

        dev_set_drvdata(&smaster->dev, &smaster[1]);

        return smaster;
}
EXPORT_SYMBOL_GPL(siox_master_alloc);

static void devm_siox_master_put(void *data)
{
        struct siox_master *smaster = data;

        siox_master_put(smaster);
}

struct siox_master *devm_siox_master_alloc(struct device *dev,
                                           size_t size)
{
        struct siox_master *smaster;
        int ret;

        smaster = siox_master_alloc(dev, size);
        if (!smaster)
                return NULL;

        ret = devm_add_action_or_reset(dev, devm_siox_master_put, smaster);
        if (ret)
                return NULL;

        return smaster;
}
EXPORT_SYMBOL_GPL(devm_siox_master_alloc);

int siox_master_register(struct siox_master *smaster)
{
        int ret;

        if (!siox_is_registered)
                return -EPROBE_DEFER;

        if (!smaster->pushpull)
                return -EINVAL;

        get_device(&smaster->dev);

        dev_set_name(&smaster->dev, "siox-%d", smaster->busno);

        mutex_init(&smaster->lock);
        INIT_LIST_HEAD(&smaster->devices);

        smaster->last_poll = jiffies;
        smaster->poll_thread = kthread_run(siox_poll_thread, smaster,
                                           "siox-%d", smaster->busno);
        if (IS_ERR(smaster->poll_thread)) {
                smaster->active = 0;
                return PTR_ERR(smaster->poll_thread);
        }

        ret = device_add(&smaster->dev);
        if (ret)
                kthread_stop(smaster->poll_thread);

        return ret;
}
EXPORT_SYMBOL_GPL(siox_master_register);

void siox_master_unregister(struct siox_master *smaster)
{
        /* remove device */
        device_del(&smaster->dev);

        siox_master_lock(smaster);

        __siox_stop(smaster);

        while (smaster->num_devices) {
                struct siox_device *sdevice;

                sdevice = container_of(smaster->devices.prev,
                                       struct siox_device, node);
                list_del(&sdevice->node);
                smaster->num_devices--;

                siox_master_unlock(smaster);

                device_unregister(&sdevice->dev);

                siox_master_lock(smaster);
        }

        siox_master_unlock(smaster);

        put_device(&smaster->dev);
}
EXPORT_SYMBOL_GPL(siox_master_unregister);

static void devm_siox_master_unregister(void *data)
{
        struct siox_master *smaster = data;

        siox_master_unregister(smaster);
}

int devm_siox_master_register(struct device *dev, struct siox_master *smaster)
{
        int ret;

        ret = siox_master_register(smaster);
        if (ret)
                return ret;

        return devm_add_action_or_reset(dev, devm_siox_master_unregister, smaster);
}
EXPORT_SYMBOL_GPL(devm_siox_master_register);

static struct siox_device *siox_device_add(struct siox_master *smaster,
                                           const char *type, size_t inbytes,
                                           size_t outbytes, u8 statustype)
{
        struct siox_device *sdevice;
        int ret;
        size_t buf_len;

        sdevice = kzalloc_obj(*sdevice);
        if (!sdevice)
                return ERR_PTR(-ENOMEM);

        sdevice->type = type;
        sdevice->inbytes = inbytes;
        sdevice->outbytes = outbytes;
        sdevice->statustype = statustype;

        sdevice->smaster = smaster;
        sdevice->dev.parent = &smaster->dev;
        sdevice->dev.bus = &siox_bus_type;
        sdevice->dev.type = &siox_device_type;

        siox_master_lock(smaster);

        dev_set_name(&sdevice->dev, "siox-%d-%d",
                     smaster->busno, smaster->num_devices);

        buf_len = smaster->setbuf_len + inbytes +
                smaster->getbuf_len + outbytes;
        if (smaster->buf_len < buf_len) {
                u8 *buf = krealloc(smaster->buf, buf_len, GFP_KERNEL);

                if (!buf) {
                        dev_err(&smaster->dev,
                                "failed to realloc buffer to %zu\n", buf_len);
                        ret = -ENOMEM;
                        goto err_buf_alloc;
                }

                smaster->buf_len = buf_len;
                smaster->buf = buf;
        }

        ret = device_register(&sdevice->dev);
        if (ret) {
                dev_err(&smaster->dev, "failed to register device: %d\n", ret);

                goto err_device_register;
        }

        smaster->num_devices++;
        list_add_tail(&sdevice->node, &smaster->devices);

        smaster->setbuf_len += sdevice->inbytes;
        smaster->getbuf_len += sdevice->outbytes;

        sdevice->status_errors_kn = sysfs_get_dirent(sdevice->dev.kobj.sd,
                                                     "status_errors");
        sdevice->watchdog_kn = sysfs_get_dirent(sdevice->dev.kobj.sd,
                                                "watchdog");
        sdevice->watchdog_errors_kn = sysfs_get_dirent(sdevice->dev.kobj.sd,
                                                       "watchdog_errors");
        sdevice->connected_kn = sysfs_get_dirent(sdevice->dev.kobj.sd,
                                                 "connected");

        siox_master_unlock(smaster);

        return sdevice;

err_device_register:
        /* don't care to make the buffer smaller again */
        put_device(&sdevice->dev);
        sdevice = NULL;

err_buf_alloc:
        siox_master_unlock(smaster);

        kfree(sdevice);

        return ERR_PTR(ret);
}

static void siox_device_remove(struct siox_master *smaster)
{
        struct siox_device *sdevice;

        siox_master_lock(smaster);

        if (!smaster->num_devices) {
                siox_master_unlock(smaster);
                return;
        }

        sdevice = container_of(smaster->devices.prev, struct siox_device, node);
        list_del(&sdevice->node);
        smaster->num_devices--;

        smaster->setbuf_len -= sdevice->inbytes;
        smaster->getbuf_len -= sdevice->outbytes;

        if (!smaster->num_devices)
                __siox_stop(smaster);

        siox_master_unlock(smaster);

        /*
         * This must be done without holding the master lock because we're
         * called from device_remove_store which also holds a sysfs mutex.
         * device_unregister tries to aquire the same lock.
         */
        device_unregister(&sdevice->dev);
}

int __siox_driver_register(struct siox_driver *sdriver, struct module *owner)
{
        int ret;

        if (unlikely(!siox_is_registered))
                return -EPROBE_DEFER;

        if (!sdriver->probe ||
            (!sdriver->set_data && !sdriver->get_data)) {
                pr_err("Driver %s doesn't provide needed callbacks\n",
                       sdriver->driver.name);
                return -EINVAL;
        }

        sdriver->driver.owner = owner;
        sdriver->driver.bus = &siox_bus_type;

        ret = driver_register(&sdriver->driver);
        if (ret)
                pr_err("Failed to register siox driver %s (%d)\n",
                       sdriver->driver.name, ret);

        return ret;
}
EXPORT_SYMBOL_GPL(__siox_driver_register);

static int __init siox_init(void)
{
        int ret;

        ret = bus_register(&siox_bus_type);
        if (ret) {
                pr_err("Registration of SIOX bus type failed: %d\n", ret);
                return ret;
        }

        siox_is_registered = true;

        return 0;
}
subsys_initcall(siox_init);

static void __exit siox_exit(void)
{
        bus_unregister(&siox_bus_type);
}
module_exit(siox_exit);

MODULE_AUTHOR("Uwe Kleine-Koenig <u.kleine-koenig@pengutronix.de>");
MODULE_DESCRIPTION("Eckelmann SIOX driver core");
MODULE_LICENSE("GPL v2");