Initial import

1 files changed, 856 insertions, 0 deletions

diff --git a/drivers/spi/spidev.c b/drivers/spi/spidev.c
new file mode 100644
index 000000000..92c909eed
--- /dev/null
+++ b/drivers/spi/spidev.c
@@ -0,0 +1,856 @@
+/*
+ * Simple synchronous userspace interface to SPI devices
+ *
+ * Copyright (C) 2006 SWAPP
+ *	Andrea Paterniani <a.paterniani@swapp-eng.it>
+ * Copyright (C) 2007 David Brownell (simplification, cleanup)
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * 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.
+ */
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/ioctl.h>
+#include <linux/fs.h>
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/list.h>
+#include <linux/errno.h>
+#include <linux/mutex.h>
+#include <linux/slab.h>
+#include <linux/compat.h>
+#include <linux/of.h>
+#include <linux/of_device.h>
+
+#include <linux/spi/spi.h>
+#include <linux/spi/spidev.h>
+
+#include <linux/uaccess.h>
+
+
+/*
+ * This supports access to SPI devices using normal userspace I/O calls.
+ * Note that while traditional UNIX/POSIX I/O semantics are half duplex,
+ * and often mask message boundaries, full SPI support requires full duplex
+ * transfers.  There are several kinds of internal message boundaries to
+ * handle chipselect management and other protocol options.
+ *
+ * SPI has a character major number assigned.  We allocate minor numbers
+ * dynamically using a bitmask.  You must use hotplug tools, such as udev
+ * (or mdev with busybox) to create and destroy the /dev/spidevB.C device
+ * nodes, since there is no fixed association of minor numbers with any
+ * particular SPI bus or device.
+ */
+#define SPIDEV_MAJOR			153	/* assigned */
+#define N_SPI_MINORS			32	/* ... up to 256 */
+
+static DECLARE_BITMAP(minors, N_SPI_MINORS);
+
+
+/* Bit masks for spi_device.mode management.  Note that incorrect
+ * settings for some settings can cause *lots* of trouble for other
+ * devices on a shared bus:
+ *
+ *  - CS_HIGH ... this device will be active when it shouldn't be
+ *  - 3WIRE ... when active, it won't behave as it should
+ *  - NO_CS ... there will be no explicit message boundaries; this
+ *	is completely incompatible with the shared bus model
+ *  - READY ... transfers may proceed when they shouldn't.
+ *
+ * REVISIT should changing those flags be privileged?
+ */
+#define SPI_MODE_MASK		(SPI_CPHA | SPI_CPOL | SPI_CS_HIGH \
+				| SPI_LSB_FIRST | SPI_3WIRE | SPI_LOOP \
+				| SPI_NO_CS | SPI_READY | SPI_TX_DUAL \
+				| SPI_TX_QUAD | SPI_RX_DUAL | SPI_RX_QUAD)
+
+struct spidev_data {
+	dev_t			devt;
+	spinlock_t		spi_lock;
+	struct spi_device	*spi;
+	struct list_head	device_entry;
+
+	/* TX/RX buffers are NULL unless this device is open (users > 0) */
+	struct mutex		buf_lock;
+	unsigned		users;
+	u8			*tx_buffer;
+	u8			*rx_buffer;
+	u32			speed_hz;
+};
+
+static LIST_HEAD(device_list);
+static DEFINE_MUTEX(device_list_lock);
+
+static unsigned bufsiz = 4096;
+module_param(bufsiz, uint, S_IRUGO);
+MODULE_PARM_DESC(bufsiz, "data bytes in biggest supported SPI message");
+
+/*-------------------------------------------------------------------------*/
+
+/*
+ * We can't use the standard synchronous wrappers for file I/O; we
+ * need to protect against async removal of the underlying spi_device.
+ */
+static void spidev_complete(void *arg)
+{
+	complete(arg);
+}
+
+static ssize_t
+spidev_sync(struct spidev_data *spidev, struct spi_message *message)
+{
+	DECLARE_COMPLETION_ONSTACK(done);
+	int status;
+
+	message->complete = spidev_complete;
+	message->context = &done;
+
+	spin_lock_irq(&spidev->spi_lock);
+	if (spidev->spi == NULL)
+		status = -ESHUTDOWN;
+	else
+		status = spi_async(spidev->spi, message);
+	spin_unlock_irq(&spidev->spi_lock);
+
+	if (status == 0) {
+		wait_for_completion(&done);
+		status = message->status;
+		if (status == 0)
+			status = message->actual_length;
+	}
+	return status;
+}
+
+static inline ssize_t
+spidev_sync_write(struct spidev_data *spidev, size_t len)
+{
+	struct spi_transfer	t = {
+			.tx_buf		= spidev->tx_buffer,
+			.len		= len,
+			.speed_hz	= spidev->speed_hz,
+		};
+	struct spi_message	m;
+
+	spi_message_init(&m);
+	spi_message_add_tail(&t, &m);
+	return spidev_sync(spidev, &m);
+}
+
+static inline ssize_t
+spidev_sync_read(struct spidev_data *spidev, size_t len)
+{
+	struct spi_transfer	t = {
+			.rx_buf		= spidev->rx_buffer,
+			.len		= len,
+			.speed_hz	= spidev->speed_hz,
+		};
+	struct spi_message	m;
+
+	spi_message_init(&m);
+	spi_message_add_tail(&t, &m);
+	return spidev_sync(spidev, &m);
+}
+
+/*-------------------------------------------------------------------------*/
+
+/* Read-only message with current device setup */
+static ssize_t
+spidev_read(struct file *filp, char __user *buf, size_t count, loff_t *f_pos)
+{
+	struct spidev_data	*spidev;
+	ssize_t			status = 0;
+
+	/* chipselect only toggles at start or end of operation */
+	if (count > bufsiz)
+		return -EMSGSIZE;
+
+	spidev = filp->private_data;
+
+	mutex_lock(&spidev->buf_lock);
+	status = spidev_sync_read(spidev, count);
+	if (status > 0) {
+		unsigned long	missing;
+
+		missing = copy_to_user(buf, spidev->rx_buffer, status);
+		if (missing == status)
+			status = -EFAULT;
+		else
+			status = status - missing;
+	}
+	mutex_unlock(&spidev->buf_lock);
+
+	return status;
+}
+
+/* Write-only message with current device setup */
+static ssize_t
+spidev_write(struct file *filp, const char __user *buf,
+		size_t count, loff_t *f_pos)
+{
+	struct spidev_data	*spidev;
+	ssize_t			status = 0;
+	unsigned long		missing;
+
+	/* chipselect only toggles at start or end of operation */
+	if (count > bufsiz)
+		return -EMSGSIZE;
+
+	spidev = filp->private_data;
+
+	mutex_lock(&spidev->buf_lock);
+	missing = copy_from_user(spidev->tx_buffer, buf, count);
+	if (missing == 0)
+		status = spidev_sync_write(spidev, count);
+	else
+		status = -EFAULT;
+	mutex_unlock(&spidev->buf_lock);
+
+	return status;
+}
+
+static int spidev_message(struct spidev_data *spidev,
+		struct spi_ioc_transfer *u_xfers, unsigned n_xfers)
+{
+	struct spi_message	msg;
+	struct spi_transfer	*k_xfers;
+	struct spi_transfer	*k_tmp;
+	struct spi_ioc_transfer *u_tmp;
+	unsigned		n, total, tx_total, rx_total;
+	u8			*tx_buf, *rx_buf;
+	int			status = -EFAULT;
+
+	spi_message_init(&msg);
+	k_xfers = kcalloc(n_xfers, sizeof(*k_tmp), GFP_KERNEL);
+	if (k_xfers == NULL)
+		return -ENOMEM;
+
+	/* Construct spi_message, copying any tx data to bounce buffer.
+	 * We walk the array of user-provided transfers, using each one
+	 * to initialize a kernel version of the same transfer.
+	 */
+	tx_buf = spidev->tx_buffer;
+	rx_buf = spidev->rx_buffer;
+	total = 0;
+	tx_total = 0;
+	rx_total = 0;
+	for (n = n_xfers, k_tmp = k_xfers, u_tmp = u_xfers;
+			n;
+			n--, k_tmp++, u_tmp++) {
+		k_tmp->len = u_tmp->len;
+
+		total += k_tmp->len;
+		/* Since the function returns the total length of transfers
+		 * on success, restrict the total to positive int values to
+		 * avoid the return value looking like an error.  Also check
+		 * each transfer length to avoid arithmetic overflow.
+		 */
+		if (total > INT_MAX || k_tmp->len > INT_MAX) {
+			status = -EMSGSIZE;
+			goto done;
+		}
+
+		if (u_tmp->rx_buf) {
+			/* this transfer needs space in RX bounce buffer */
+			rx_total += k_tmp->len;
+			if (rx_total > bufsiz) {
+				status = -EMSGSIZE;
+				goto done;
+			}
+			k_tmp->rx_buf = rx_buf;
+			if (!access_ok(VERIFY_WRITE, (u8 __user *)
+						(uintptr_t) u_tmp->rx_buf,
+						u_tmp->len))
+				goto done;
+			rx_buf += k_tmp->len;
+		}
+		if (u_tmp->tx_buf) {
+			/* this transfer needs space in TX bounce buffer */
+			tx_total += k_tmp->len;
+			if (tx_total > bufsiz) {
+				status = -EMSGSIZE;
+				goto done;
+			}
+			k_tmp->tx_buf = tx_buf;
+			if (copy_from_user(tx_buf, (const u8 __user *)
+						(uintptr_t) u_tmp->tx_buf,
+					u_tmp->len))
+				goto done;
+			tx_buf += k_tmp->len;
+		}
+
+		k_tmp->cs_change = !!u_tmp->cs_change;
+		k_tmp->tx_nbits = u_tmp->tx_nbits;
+		k_tmp->rx_nbits = u_tmp->rx_nbits;
+		k_tmp->bits_per_word = u_tmp->bits_per_word;
+		k_tmp->delay_usecs = u_tmp->delay_usecs;
+		k_tmp->speed_hz = u_tmp->speed_hz;
+		if (!k_tmp->speed_hz)
+			k_tmp->speed_hz = spidev->speed_hz;
+#ifdef VERBOSE
+		dev_dbg(&spidev->spi->dev,
+			"  xfer len %zd %s%s%s%dbits %u usec %uHz\n",
+			u_tmp->len,
+			u_tmp->rx_buf ? "rx " : "",
+			u_tmp->tx_buf ? "tx " : "",
+			u_tmp->cs_change ? "cs " : "",
+			u_tmp->bits_per_word ? : spidev->spi->bits_per_word,
+			u_tmp->delay_usecs,
+			u_tmp->speed_hz ? : spidev->spi->max_speed_hz);
+#endif
+		spi_message_add_tail(k_tmp, &msg);
+	}
+
+	status = spidev_sync(spidev, &msg);
+	if (status < 0)
+		goto done;
+
+	/* copy any rx data out of bounce buffer */
+	rx_buf = spidev->rx_buffer;
+	for (n = n_xfers, u_tmp = u_xfers; n; n--, u_tmp++) {
+		if (u_tmp->rx_buf) {
+			if (__copy_to_user((u8 __user *)
+					(uintptr_t) u_tmp->rx_buf, rx_buf,
+					u_tmp->len)) {
+				status = -EFAULT;
+				goto done;
+			}
+			rx_buf += u_tmp->len;
+		}
+	}
+	status = total;
+
+done:
+	kfree(k_xfers);
+	return status;
+}
+
+static struct spi_ioc_transfer *
+spidev_get_ioc_message(unsigned int cmd, struct spi_ioc_transfer __user *u_ioc,
+		unsigned *n_ioc)
+{
+	struct spi_ioc_transfer	*ioc;
+	u32	tmp;
+
+	/* Check type, command number and direction */
+	if (_IOC_TYPE(cmd) != SPI_IOC_MAGIC
+			|| _IOC_NR(cmd) != _IOC_NR(SPI_IOC_MESSAGE(0))
+			|| _IOC_DIR(cmd) != _IOC_WRITE)
+		return ERR_PTR(-ENOTTY);
+
+	tmp = _IOC_SIZE(cmd);
+	if ((tmp % sizeof(struct spi_ioc_transfer)) != 0)
+		return ERR_PTR(-EINVAL);
+	*n_ioc = tmp / sizeof(struct spi_ioc_transfer);
+	if (*n_ioc == 0)
+		return NULL;
+
+	/* copy into scratch area */
+	ioc = kmalloc(tmp, GFP_KERNEL);
+	if (!ioc)
+		return ERR_PTR(-ENOMEM);
+	if (__copy_from_user(ioc, u_ioc, tmp)) {
+		kfree(ioc);
+		return ERR_PTR(-EFAULT);
+	}
+	return ioc;
+}
+
+static long
+spidev_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
+{
+	int			err = 0;
+	int			retval = 0;
+	struct spidev_data	*spidev;
+	struct spi_device	*spi;
+	u32			tmp;
+	unsigned		n_ioc;
+	struct spi_ioc_transfer	*ioc;
+
+	/* Check type and command number */
+	if (_IOC_TYPE(cmd) != SPI_IOC_MAGIC)
+		return -ENOTTY;
+
+	/* Check access direction once here; don't repeat below.
+	 * IOC_DIR is from the user perspective, while access_ok is
+	 * from the kernel perspective; so they look reversed.
+	 */
+	if (_IOC_DIR(cmd) & _IOC_READ)
+		err = !access_ok(VERIFY_WRITE,
+				(void __user *)arg, _IOC_SIZE(cmd));
+	if (err == 0 && _IOC_DIR(cmd) & _IOC_WRITE)
+		err = !access_ok(VERIFY_READ,
+				(void __user *)arg, _IOC_SIZE(cmd));
+	if (err)
+		return -EFAULT;
+
+	/* guard against device removal before, or while,
+	 * we issue this ioctl.
+	 */
+	spidev = filp->private_data;
+	spin_lock_irq(&spidev->spi_lock);
+	spi = spi_dev_get(spidev->spi);
+	spin_unlock_irq(&spidev->spi_lock);
+
+	if (spi == NULL)
+		return -ESHUTDOWN;
+
+	/* use the buffer lock here for triple duty:
+	 *  - prevent I/O (from us) so calling spi_setup() is safe;
+	 *  - prevent concurrent SPI_IOC_WR_* from morphing
+	 *    data fields while SPI_IOC_RD_* reads them;
+	 *  - SPI_IOC_MESSAGE needs the buffer locked "normally".
+	 */
+	mutex_lock(&spidev->buf_lock);
+
+	switch (cmd) {
+	/* read requests */
+	case SPI_IOC_RD_MODE:
+		retval = __put_user(spi->mode & SPI_MODE_MASK,
+					(__u8 __user *)arg);
+		break;
+	case SPI_IOC_RD_MODE32:
+		retval = __put_user(spi->mode & SPI_MODE_MASK,
+					(__u32 __user *)arg);
+		break;
+	case SPI_IOC_RD_LSB_FIRST:
+		retval = __put_user((spi->mode & SPI_LSB_FIRST) ?  1 : 0,
+					(__u8 __user *)arg);
+		break;
+	case SPI_IOC_RD_BITS_PER_WORD:
+		retval = __put_user(spi->bits_per_word, (__u8 __user *)arg);
+		break;
+	case SPI_IOC_RD_MAX_SPEED_HZ:
+		retval = __put_user(spidev->speed_hz, (__u32 __user *)arg);
+		break;
+
+	/* write requests */
+	case SPI_IOC_WR_MODE:
+	case SPI_IOC_WR_MODE32:
+		if (cmd == SPI_IOC_WR_MODE)
+			retval = __get_user(tmp, (u8 __user *)arg);
+		else
+			retval = __get_user(tmp, (u32 __user *)arg);
+		if (retval == 0) {
+			u32	save = spi->mode;
+
+			if (tmp & ~SPI_MODE_MASK) {
+				retval = -EINVAL;
+				break;
+			}
+
+			tmp |= spi->mode & ~SPI_MODE_MASK;
+			spi->mode = (u16)tmp;
+			retval = spi_setup(spi);
+			if (retval < 0)
+				spi->mode = save;
+			else
+				dev_dbg(&spi->dev, "spi mode %x\n", tmp);
+		}
+		break;
+	case SPI_IOC_WR_LSB_FIRST:
+		retval = __get_user(tmp, (__u8 __user *)arg);
+		if (retval == 0) {
+			u32	save = spi->mode;
+
+			if (tmp)
+				spi->mode |= SPI_LSB_FIRST;
+			else
+				spi->mode &= ~SPI_LSB_FIRST;
+			retval = spi_setup(spi);
+			if (retval < 0)
+				spi->mode = save;
+			else
+				dev_dbg(&spi->dev, "%csb first\n",
+						tmp ? 'l' : 'm');
+		}
+		break;
+	case SPI_IOC_WR_BITS_PER_WORD:
+		retval = __get_user(tmp, (__u8 __user *)arg);
+		if (retval == 0) {
+			u8	save = spi->bits_per_word;
+
+			spi->bits_per_word = tmp;
+			retval = spi_setup(spi);
+			if (retval < 0)
+				spi->bits_per_word = save;
+			else
+				dev_dbg(&spi->dev, "%d bits per word\n", tmp);
+		}
+		break;
+	case SPI_IOC_WR_MAX_SPEED_HZ:
+		retval = __get_user(tmp, (__u32 __user *)arg);
+		if (retval == 0) {
+			u32	save = spi->max_speed_hz;
+
+			spi->max_speed_hz = tmp;
+			retval = spi_setup(spi);
+			if (retval >= 0)
+				spidev->speed_hz = tmp;
+			else
+				dev_dbg(&spi->dev, "%d Hz (max)\n", tmp);
+			spi->max_speed_hz = save;
+		}
+		break;
+
+	default:
+		/* segmented and/or full-duplex I/O request */
+		/* Check message and copy into scratch area */
+		ioc = spidev_get_ioc_message(cmd,
+				(struct spi_ioc_transfer __user *)arg, &n_ioc);
+		if (IS_ERR(ioc)) {
+			retval = PTR_ERR(ioc);
+			break;
+		}
+		if (!ioc)
+			break;	/* n_ioc is also 0 */
+
+		/* translate to spi_message, execute */
+		retval = spidev_message(spidev, ioc, n_ioc);
+		kfree(ioc);
+		break;
+	}
+
+	mutex_unlock(&spidev->buf_lock);
+	spi_dev_put(spi);
+	return retval;
+}
+
+#ifdef CONFIG_COMPAT
+static long
+spidev_compat_ioc_message(struct file *filp, unsigned int cmd,
+		unsigned long arg)
+{
+	struct spi_ioc_transfer __user	*u_ioc;
+	int				retval = 0;
+	struct spidev_data		*spidev;
+	struct spi_device		*spi;
+	unsigned			n_ioc, n;
+	struct spi_ioc_transfer		*ioc;
+
+	u_ioc = (struct spi_ioc_transfer __user *) compat_ptr(arg);
+	if (!access_ok(VERIFY_READ, u_ioc, _IOC_SIZE(cmd)))
+		return -EFAULT;
+
+	/* guard against device removal before, or while,
+	 * we issue this ioctl.
+	 */
+	spidev = filp->private_data;
+	spin_lock_irq(&spidev->spi_lock);
+	spi = spi_dev_get(spidev->spi);
+	spin_unlock_irq(&spidev->spi_lock);
+
+	if (spi == NULL)
+		return -ESHUTDOWN;
+
+	/* SPI_IOC_MESSAGE needs the buffer locked "normally" */
+	mutex_lock(&spidev->buf_lock);
+
+	/* Check message and copy into scratch area */
+	ioc = spidev_get_ioc_message(cmd, u_ioc, &n_ioc);
+	if (IS_ERR(ioc)) {
+		retval = PTR_ERR(ioc);
+		goto done;
+	}
+	if (!ioc)
+		goto done;	/* n_ioc is also 0 */
+
+	/* Convert buffer pointers */
+	for (n = 0; n < n_ioc; n++) {
+		ioc[n].rx_buf = (uintptr_t) compat_ptr(ioc[n].rx_buf);
+		ioc[n].tx_buf = (uintptr_t) compat_ptr(ioc[n].tx_buf);
+	}
+
+	/* translate to spi_message, execute */
+	retval = spidev_message(spidev, ioc, n_ioc);
+	kfree(ioc);
+
+done:
+	mutex_unlock(&spidev->buf_lock);
+	spi_dev_put(spi);
+	return retval;
+}
+
+static long
+spidev_compat_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
+{
+	if (_IOC_TYPE(cmd) == SPI_IOC_MAGIC
+			&& _IOC_NR(cmd) == _IOC_NR(SPI_IOC_MESSAGE(0))
+			&& _IOC_DIR(cmd) == _IOC_WRITE)
+		return spidev_compat_ioc_message(filp, cmd, arg);
+
+	return spidev_ioctl(filp, cmd, (unsigned long)compat_ptr(arg));
+}
+#else
+#define spidev_compat_ioctl NULL
+#endif /* CONFIG_COMPAT */
+
+static int spidev_open(struct inode *inode, struct file *filp)
+{
+	struct spidev_data	*spidev;
+	int			status = -ENXIO;
+
+	mutex_lock(&device_list_lock);
+
+	list_for_each_entry(spidev, &device_list, device_entry) {
+		if (spidev->devt == inode->i_rdev) {
+			status = 0;
+			break;
+		}
+	}
+
+	if (status) {
+		pr_debug("spidev: nothing for minor %d\n", iminor(inode));
+		goto err_find_dev;
+	}
+
+	if (!spidev->tx_buffer) {
+		spidev->tx_buffer = kmalloc(bufsiz, GFP_KERNEL);
+		if (!spidev->tx_buffer) {
+				dev_dbg(&spidev->spi->dev, "open/ENOMEM\n");
+				status = -ENOMEM;
+			goto err_find_dev;
+			}
+		}
+
+	if (!spidev->rx_buffer) {
+		spidev->rx_buffer = kmalloc(bufsiz, GFP_KERNEL);
+		if (!spidev->rx_buffer) {
+			dev_dbg(&spidev->spi->dev, "open/ENOMEM\n");
+			status = -ENOMEM;
+			goto err_alloc_rx_buf;
+		}
+	}
+
+	spidev->users++;
+	filp->private_data = spidev;
+	nonseekable_open(inode, filp);
+
+	mutex_unlock(&device_list_lock);
+	return 0;
+
+err_alloc_rx_buf:
+	kfree(spidev->tx_buffer);
+	spidev->tx_buffer = NULL;
+err_find_dev:
+	mutex_unlock(&device_list_lock);
+	return status;
+}
+
+static int spidev_release(struct inode *inode, struct file *filp)
+{
+	struct spidev_data	*spidev;
+	int			status = 0;
+
+	mutex_lock(&device_list_lock);
+	spidev = filp->private_data;
+	filp->private_data = NULL;
+
+	/* last close? */
+	spidev->users--;
+	if (!spidev->users) {
+		int		dofree;
+
+		kfree(spidev->tx_buffer);
+		spidev->tx_buffer = NULL;
+
+		kfree(spidev->rx_buffer);
+		spidev->rx_buffer = NULL;
+
+		spidev->speed_hz = spidev->spi->max_speed_hz;
+
+		/* ... after we unbound from the underlying device? */
+		spin_lock_irq(&spidev->spi_lock);
+		dofree = (spidev->spi == NULL);
+		spin_unlock_irq(&spidev->spi_lock);
+
+		if (dofree)
+			kfree(spidev);
+	}
+	mutex_unlock(&device_list_lock);
+
+	return status;
+}
+
+static const struct file_operations spidev_fops = {
+	.owner =	THIS_MODULE,
+	/* REVISIT switch to aio primitives, so that userspace
+	 * gets more complete API coverage.  It'll simplify things
+	 * too, except for the locking.
+	 */
+	.write =	spidev_write,
+	.read =		spidev_read,
+	.unlocked_ioctl = spidev_ioctl,
+	.compat_ioctl = spidev_compat_ioctl,
+	.open =		spidev_open,
+	.release =	spidev_release,
+	.llseek =	no_llseek,
+};
+
+/*-------------------------------------------------------------------------*/
+
+/* The main reason to have this class is to make mdev/udev create the
+ * /dev/spidevB.C character device nodes exposing our userspace API.
+ * It also simplifies memory management.
+ */
+
+static struct class *spidev_class;
+
+#ifdef CONFIG_OF
+static const struct of_device_id spidev_dt_ids[] = {
+	{ .compatible = "rohm,dh2228fv" },
+	{},
+};
+MODULE_DEVICE_TABLE(of, spidev_dt_ids);
+#endif
+
+/*-------------------------------------------------------------------------*/
+
+static int spidev_probe(struct spi_device *spi)
+{
+	struct spidev_data	*spidev;
+	int			status;
+	unsigned long		minor;
+
+	/*
+	 * spidev should never be referenced in DT without a specific
+	 * compatbile string, it is a Linux implementation thing
+	 * rather than a description of the hardware.
+	 */
+	if (spi->dev.of_node && !of_match_device(spidev_dt_ids, &spi->dev)) {
+		dev_err(&spi->dev, "buggy DT: spidev listed directly in DT\n");
+		WARN_ON(spi->dev.of_node &&
+			!of_match_device(spidev_dt_ids, &spi->dev));
+	}
+
+	/* Allocate driver data */
+	spidev = kzalloc(sizeof(*spidev), GFP_KERNEL);
+	if (!spidev)
+		return -ENOMEM;
+
+	/* Initialize the driver data */
+	spidev->spi = spi;
+	spin_lock_init(&spidev->spi_lock);
+	mutex_init(&spidev->buf_lock);
+
+	INIT_LIST_HEAD(&spidev->device_entry);
+
+	/* If we can allocate a minor number, hook up this device.
+	 * Reusing minors is fine so long as udev or mdev is working.
+	 */
+	mutex_lock(&device_list_lock);
+	minor = find_first_zero_bit(minors, N_SPI_MINORS);
+	if (minor < N_SPI_MINORS) {
+		struct device *dev;
+
+		spidev->devt = MKDEV(SPIDEV_MAJOR, minor);
+		dev = device_create(spidev_class, &spi->dev, spidev->devt,
+				    spidev, "spidev%d.%d",
+				    spi->master->bus_num, spi->chip_select);
+		status = PTR_ERR_OR_ZERO(dev);
+	} else {
+		dev_dbg(&spi->dev, "no minor number available!\n");
+		status = -ENODEV;
+	}
+	if (status == 0) {
+		set_bit(minor, minors);
+		list_add(&spidev->device_entry, &device_list);
+	}
+	mutex_unlock(&device_list_lock);
+
+	spidev->speed_hz = spi->max_speed_hz;
+
+	if (status == 0)
+		spi_set_drvdata(spi, spidev);
+	else
+		kfree(spidev);
+
+	return status;
+}
+
+static int spidev_remove(struct spi_device *spi)
+{
+	struct spidev_data	*spidev = spi_get_drvdata(spi);
+
+	/* make sure ops on existing fds can abort cleanly */
+	spin_lock_irq(&spidev->spi_lock);
+	spidev->spi = NULL;
+	spin_unlock_irq(&spidev->spi_lock);
+
+	/* prevent new opens */
+	mutex_lock(&device_list_lock);
+	list_del(&spidev->device_entry);
+	device_destroy(spidev_class, spidev->devt);
+	clear_bit(MINOR(spidev->devt), minors);
+	if (spidev->users == 0)
+		kfree(spidev);
+	mutex_unlock(&device_list_lock);
+
+	return 0;
+}
+
+static struct spi_driver spidev_spi_driver = {
+	.driver = {
+		.name =		"spidev",
+		.owner =	THIS_MODULE,
+		.of_match_table = of_match_ptr(spidev_dt_ids),
+	},
+	.probe =	spidev_probe,
+	.remove =	spidev_remove,
+
+	/* NOTE:  suspend/resume methods are not necessary here.
+	 * We don't do anything except pass the requests to/from
+	 * the underlying controller.  The refrigerator handles
+	 * most issues; the controller driver handles the rest.
+	 */
+};
+
+/*-------------------------------------------------------------------------*/
+
+static int __init spidev_init(void)
+{
+	int status;
+
+	/* Claim our 256 reserved device numbers.  Then register a class
+	 * that will key udev/mdev to add/remove /dev nodes.  Last, register
+	 * the driver which manages those device numbers.
+	 */
+	BUILD_BUG_ON(N_SPI_MINORS > 256);
+	status = register_chrdev(SPIDEV_MAJOR, "spi", &spidev_fops);
+	if (status < 0)
+		return status;
+
+	spidev_class = class_create(THIS_MODULE, "spidev");
+	if (IS_ERR(spidev_class)) {
+		unregister_chrdev(SPIDEV_MAJOR, spidev_spi_driver.driver.name);
+		return PTR_ERR(spidev_class);
+	}
+
+	status = spi_register_driver(&spidev_spi_driver);
+	if (status < 0) {
+		class_destroy(spidev_class);
+		unregister_chrdev(SPIDEV_MAJOR, spidev_spi_driver.driver.name);
+	}
+	return status;
+}
+module_init(spidev_init);
+
+static void __exit spidev_exit(void)
+{
+	spi_unregister_driver(&spidev_spi_driver);
+	class_destroy(spidev_class);
+	unregister_chrdev(SPIDEV_MAJOR, spidev_spi_driver.driver.name);
+}
+module_exit(spidev_exit);
+
+MODULE_AUTHOR("Andrea Paterniani, <a.paterniani@swapp-eng.it>");
+MODULE_DESCRIPTION("User mode SPI device interface");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("spi:spidev");