[PATCH] spi: simple SPI framework

This is the core of a small SPI framework, implementing the model of a
queue of messages which complete asynchronously (with thin synchronous
wrappers on top).

  - It's still less than 2KB of ".text" (ARM).  If there's got to be a
    mid-layer for something so simple, that's the right size budget.  :)

  - The guts use board-specific SPI device tables to build the driver
    model tree.  (Hardware probing is rarely an option.)

  - This version of Kconfig includes no drivers.  At this writing there
    are two known master controller drivers (PXA/SSP, OMAP MicroWire)
    and three protocol drivers (CS8415a, ADS7846, DataFlash) with LKML
    mentions of other drivers in development.

  - No userspace API.  There are several implementations to compare.
    Implement them like any other driver, and bind them with sysfs.

The changes from last version posted to LKML (on 11-Nov-2005) are minor,
and include:

  - One bugfix (removes a FIXME), with the visible effect of making device
    names be "spiB.C" where B is the bus number and C is the chipselect.

  - The "caller provides DMA mappings" mechanism now has kerneldoc, for
    DMA drivers that want to be fancy.

  - Hey, the framework init can be subsys_init.  Even though board init
    logic fires earlier, at arch_init ... since the framework init is
    for driver support, and the board init support uses static init.

  - Various additional spec/doc clarifications based on discussions
    with other folk.  It adds a brief "thank you" at the end, for folk
    who've helped nudge this framework into existence.

As I've said before, I think that "protocol tweaking" is the main support
that this driver framework will need to evolve.

From: Mark Underwood <basicmark@yahoo.com>

  Update the SPI framework to remove a potential priority inversion case by
  reverting to kmalloc if the pre-allocated DMA-safe buffer isn't available.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

5 files changed, 670 insertions, 0 deletions

diff --git a/drivers/Kconfig b/drivers/Kconfig
index 48f446d3c671..283c089537bc 100644
--- a/drivers/Kconfig
+++ b/drivers/Kconfig
@@ -44,6 +44,8 @@ source "drivers/char/Kconfig"
 
 source "drivers/i2c/Kconfig"
 
+source "drivers/spi/Kconfig"
+
 source "drivers/w1/Kconfig"
 
 source "drivers/hwmon/Kconfig"
diff --git a/drivers/Makefile b/drivers/Makefile
index 7fc3f0f08b29..7c45050ecd03 100644
--- a/drivers/Makefile
+++ b/drivers/Makefile
@@ -41,6 +41,7 @@ obj-$(CONFIG_FUSION)		+= message/
 obj-$(CONFIG_IEEE1394)          += ieee1394/
 obj-y                           += cdrom/
 obj-$(CONFIG_MTD)               += mtd/
+obj-$(CONFIG_SPI)               += spi/
 obj-$(CONFIG_PCCARD)            += pcmcia/
 obj-$(CONFIG_DIO)               += dio/
 obj-$(CONFIG_SBUS)              += sbus/
diff --git a/drivers/spi/Kconfig b/drivers/spi/Kconfig
new file mode 100644
index 000000000000..d3105104a297
--- /dev/null
+++ b/drivers/spi/Kconfig
@@ -0,0 +1,76 @@
+#
+# SPI driver configuration
+#
+# NOTE:  the reason this doesn't show SPI slave support is mostly that
+# nobody's needed a slave side API yet.  The master-role API is not
+# fully appropriate there, so it'd need some thought to do well.
+#
+menu "SPI support"
+
+config SPI
+        bool "SPI support"
+        help
+          The "Serial Peripheral Interface" is a low level synchronous
+          protocol.  Chips that support SPI can have data transfer rates
+          up to several tens of Mbit/sec.  Chips are addressed with a
+          controller and a chipselect.  Most SPI slaves don't support
+          dynamic device discovery; some are even write-only or read-only.
+
+          SPI is widely used by microcontollers to talk with sensors,
+          eeprom and flash memory, codecs and various other controller
+          chips, analog to digital (and d-to-a) converters, and more.
+          MMC and SD cards can be accessed using SPI protocol; and for
+          DataFlash cards used in MMC sockets, SPI must always be used.
+
+          SPI is one of a family of similar protocols using a four wire
+          interface (select, clock, data in, data out) including Microwire
+          (half duplex), SSP, SSI, and PSP.  This driver framework should
+          work with most such devices and controllers.
+
+config SPI_DEBUG
+        boolean "Debug support for SPI drivers"
+        depends on SPI && DEBUG_KERNEL
+        help
+          Say "yes" to enable debug messaging (like dev_dbg and pr_debug),
+          sysfs, and debugfs support in SPI controller and protocol drivers.
+
+#
+# MASTER side ... talking to discrete SPI slave chips including microcontrollers
+#
+
+config SPI_MASTER
+#       boolean "SPI Master Support"
+        boolean
+        default SPI
+        help
+          If your system has an master-capable SPI controller (which
+          provides the clock and chipselect), you can enable that
+          controller and the protocol drivers for the SPI slave chips
+          that are connected.
+
+comment "SPI Master Controller Drivers"
+        depends on SPI_MASTER
+
+
+#
+# Add new SPI master controllers in alphabetical order above this line
+#
+
+
+#
+# There are lots of SPI device types, with sensors and memory
+# being probably the most widely used ones.
+#
+comment "SPI Protocol Masters"
+        depends on SPI_MASTER
+
+
+#
+# Add new SPI protocol masters in alphabetical order above this line
+#
+
+
+# (slave support would go here)
+
+endmenu # "SPI support"
+
diff --git a/drivers/spi/Makefile b/drivers/spi/Makefile
new file mode 100644
index 000000000000..afd2321753b3
--- /dev/null
+++ b/drivers/spi/Makefile
@@ -0,0 +1,23 @@
+#
+# Makefile for kernel SPI drivers.
+#
+
+ifeq ($(CONFIG_SPI_DEBUG),y)
+EXTRA_CFLAGS += -DDEBUG
+endif
+
+# small core, mostly translating board-specific
+# config declarations into driver model code
+obj-$(CONFIG_SPI_MASTER)                += spi.o
+
+# SPI master controller drivers (bus)
+#       ... add above this line ...
+
+# SPI protocol drivers (device/link on bus)
+#       ... add above this line ...
+
+# SPI slave controller drivers (upstream link)
+#       ... add above this line ...
+
+# SPI slave drivers (protocol for that link)
+#       ... add above this line ...
diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
new file mode 100644
index 000000000000..7cd356b17644
--- /dev/null
+++ b/drivers/spi/spi.c
@@ -0,0 +1,568 @@
+/*
+ * spi.c - SPI init/core code
+ *
+ * Copyright (C) 2005 David Brownell
+ *
+ * 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.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#include <linux/autoconf.h>
+#include <linux/kernel.h>
+#include <linux/device.h>
+#include <linux/init.h>
+#include <linux/cache.h>
+#include <linux/spi/spi.h>
+
+
+/* SPI bustype and spi_master class are registered during early boot,
+ * usually before board init code provides the SPI device tables, and
+ * are available later when driver init code needs them.
+ *
+ * Drivers for SPI devices started out like those for platform bus
+ * devices.  But both have changed in 2.6.15; maybe this should get
+ * an "spi_driver" structure at some point (not currently needed)
+ */
+static void spidev_release(struct device *dev)
+{
+        const struct spi_device *spi = to_spi_device(dev);
+
+        /* spi masters may cleanup for released devices */
+        if (spi->master->cleanup)
+                spi->master->cleanup(spi);
+
+        class_device_put(&spi->master->cdev);
+        kfree(dev);
+}
+
+static ssize_t
+modalias_show(struct device *dev, struct device_attribute *a, char *buf)
+{
+        const struct spi_device *spi = to_spi_device(dev);
+
+        return snprintf(buf, BUS_ID_SIZE + 1, "%s\n", spi->modalias);
+}
+
+static struct device_attribute spi_dev_attrs[] = {
+        __ATTR_RO(modalias),
+        __ATTR_NULL,
+};
+
+/* modalias support makes "modprobe $MODALIAS" new-style hotplug work,
+ * and the sysfs version makes coldplug work too.
+ */
+
+static int spi_match_device(struct device *dev, struct device_driver *drv)
+{
+        const struct spi_device *spi = to_spi_device(dev);
+
+        return strncmp(spi->modalias, drv->name, BUS_ID_SIZE) == 0;
+}
+
+static int spi_uevent(struct device *dev, char **envp, int num_envp,
+                char *buffer, int buffer_size)
+{
+        const struct spi_device         *spi = to_spi_device(dev);
+
+        envp[0] = buffer;
+        snprintf(buffer, buffer_size, "MODALIAS=%s", spi->modalias);
+        envp[1] = NULL;
+        return 0;
+}
+
+#ifdef  CONFIG_PM
+
+/* Suspend/resume in "struct device_driver" don't really need that
+ * strange third parameter, so we just make it a constant and expect
+ * SPI drivers to ignore it just like most platform drivers do.
+ *
+ * NOTE:  the suspend() method for an spi_master controller driver
+ * should verify that all its child devices are marked as suspended;
+ * suspend requests delivered through sysfs power/state files don't
+ * enforce such constraints.
+ */
+static int spi_suspend(struct device *dev, pm_message_t message)
+{
+        int     value;
+
+        if (!dev->driver || !dev->driver->suspend)
+                return 0;
+
+        /* suspend will stop irqs and dma; no more i/o */
+        value = dev->driver->suspend(dev, message);
+        if (value == 0)
+                dev->power.power_state = message;
+        return value;
+}
+
+static int spi_resume(struct device *dev)
+{
+        int     value;
+
+        if (!dev->driver || !dev->driver->resume)
+                return 0;
+
+        /* resume may restart the i/o queue */
+        value = dev->driver->resume(dev);
+        if (value == 0)
+                dev->power.power_state = PMSG_ON;
+        return value;
+}
+
+#else
+#define spi_suspend     NULL
+#define spi_resume      NULL
+#endif
+
+struct bus_type spi_bus_type = {
+        .name           = "spi",
+        .dev_attrs      = spi_dev_attrs,
+        .match          = spi_match_device,
+        .uevent         = spi_uevent,
+        .suspend        = spi_suspend,
+        .resume         = spi_resume,
+};
+EXPORT_SYMBOL_GPL(spi_bus_type);
+
+/*-------------------------------------------------------------------------*/
+
+/* SPI devices should normally not be created by SPI device drivers; that
+ * would make them board-specific.  Similarly with SPI master drivers.
+ * Device registration normally goes into like arch/.../mach.../board-YYY.c
+ * with other readonly (flashable) information about mainboard devices.
+ */
+
+struct boardinfo {
+        struct list_head        list;
+        unsigned                n_board_info;
+        struct spi_board_info   board_info[0];
+};
+
+static LIST_HEAD(board_list);
+static DECLARE_MUTEX(board_lock);
+
+
+/* On typical mainboards, this is purely internal; and it's not needed
+ * after board init creates the hard-wired devices.  Some development
+ * platforms may not be able to use spi_register_board_info though, and
+ * this is exported so that for example a USB or parport based adapter
+ * driver could add devices (which it would learn about out-of-band).
+ */
+struct spi_device *__init_or_module
+spi_new_device(struct spi_master *master, struct spi_board_info *chip)
+{
+        struct spi_device       *proxy;
+        struct device           *dev = master->cdev.dev;
+        int                     status;
+
+        /* NOTE:  caller did any chip->bus_num checks necessary */
+
+        if (!class_device_get(&master->cdev))
+                return NULL;
+
+        proxy = kzalloc(sizeof *proxy, GFP_KERNEL);
+        if (!proxy) {
+                dev_err(dev, "can't alloc dev for cs%d\n",
+                        chip->chip_select);
+                goto fail;
+        }
+        proxy->master = master;
+        proxy->chip_select = chip->chip_select;
+        proxy->max_speed_hz = chip->max_speed_hz;
+        proxy->irq = chip->irq;
+        proxy->modalias = chip->modalias;
+
+        snprintf(proxy->dev.bus_id, sizeof proxy->dev.bus_id,
+                        "%s.%u", master->cdev.class_id,
+                        chip->chip_select);
+        proxy->dev.parent = dev;
+        proxy->dev.bus = &spi_bus_type;
+        proxy->dev.platform_data = (void *) chip->platform_data;
+        proxy->controller_data = chip->controller_data;
+        proxy->controller_state = NULL;
+        proxy->dev.release = spidev_release;
+
+        /* drivers may modify this default i/o setup */
+        status = master->setup(proxy);
+        if (status < 0) {
+                dev_dbg(dev, "can't %s %s, status %d\n",
+                                "setup", proxy->dev.bus_id, status);
+                goto fail;
+        }
+
+        /* driver core catches callers that misbehave by defining
+         * devices that already exist.
+         */
+        status = device_register(&proxy->dev);
+        if (status < 0) {
+                dev_dbg(dev, "can't %s %s, status %d\n",
+                                "add", proxy->dev.bus_id, status);
+fail:
+                class_device_put(&master->cdev);
+                kfree(proxy);
+                return NULL;
+        }
+        dev_dbg(dev, "registered child %s\n", proxy->dev.bus_id);
+        return proxy;
+}
+EXPORT_SYMBOL_GPL(spi_new_device);
+
+/*
+ * Board-specific early init code calls this (probably during arch_initcall)
+ * with segments of the SPI device table.  Any device nodes are created later,
+ * after the relevant parent SPI controller (bus_num) is defined.  We keep
+ * this table of devices forever, so that reloading a controller driver will
+ * not make Linux forget about these hard-wired devices.
+ *
+ * Other code can also call this, e.g. a particular add-on board might provide
+ * SPI devices through its expansion connector, so code initializing that board
+ * would naturally declare its SPI devices.
+ *
+ * The board info passed can safely be __initdata ... but be careful of
+ * any embedded pointers (platform_data, etc), they're copied as-is.
+ */
+int __init
+spi_register_board_info(struct spi_board_info const *info, unsigned n)
+{
+        struct boardinfo        *bi;
+
+        bi = kmalloc (sizeof (*bi) + n * sizeof (*info), GFP_KERNEL);
+        if (!bi)
+                return -ENOMEM;
+        bi->n_board_info = n;
+        memcpy(bi->board_info, info, n * sizeof (*info));
+
+        down(&board_lock);
+        list_add_tail(&bi->list, &board_list);
+        up(&board_lock);
+        return 0;
+}
+EXPORT_SYMBOL_GPL(spi_register_board_info);
+
+/* FIXME someone should add support for a __setup("spi", ...) that
+ * creates board info from kernel command lines
+ */
+
+static void __init_or_module
+scan_boardinfo(struct spi_master *master)
+{
+        struct boardinfo        *bi;
+        struct device           *dev = master->cdev.dev;
+
+        down(&board_lock);
+        list_for_each_entry(bi, &board_list, list) {
+                struct spi_board_info   *chip = bi->board_info;
+                unsigned                n;
+
+                for (n = bi->n_board_info; n > 0; n--, chip++) {
+                        if (chip->bus_num != master->bus_num)
+                                continue;
+                        /* some controllers only have one chip, so they
+                         * might not use chipselects.  otherwise, the
+                         * chipselects are numbered 0..max.
+                         */
+                        if (chip->chip_select >= master->num_chipselect
+                                        && master->num_chipselect) {
+                                dev_dbg(dev, "cs%d > max %d\n",
+                                        chip->chip_select,
+                                        master->num_chipselect);
+                                continue;
+                        }
+                        (void) spi_new_device(master, chip);
+                }
+        }
+        up(&board_lock);
+}
+
+/*-------------------------------------------------------------------------*/
+
+static void spi_master_release(struct class_device *cdev)
+{
+        struct spi_master *master;
+
+        master = container_of(cdev, struct spi_master, cdev);
+        put_device(master->cdev.dev);
+        master->cdev.dev = NULL;
+        kfree(master);
+}
+
+static struct class spi_master_class = {
+        .name           = "spi_master",
+        .owner          = THIS_MODULE,
+        .release        = spi_master_release,
+};
+
+
+/**
+ * spi_alloc_master - allocate SPI master controller
+ * @dev: the controller, possibly using the platform_bus
+ * @size: how much driver-private data to preallocate; a pointer to this
+ *      memory in the class_data field of the returned class_device
+ *
+ * This call is used only by SPI master controller drivers, which are the
+ * only ones directly touching chip registers.  It's how they allocate
+ * an spi_master structure, prior to calling spi_add_master().
+ *
+ * This must be called from context that can sleep.  It returns the SPI
+ * master structure on success, else NULL.
+ *
+ * The caller is responsible for assigning the bus number and initializing
+ * the master's methods before calling spi_add_master(), or else (on error)
+ * calling class_device_put() to prevent a memory leak.
+ */
+struct spi_master * __init_or_module
+spi_alloc_master(struct device *dev, unsigned size)
+{
+        struct spi_master       *master;
+
+        master = kzalloc(size + sizeof *master, SLAB_KERNEL);
+        if (!master)
+                return NULL;
+
+        master->cdev.class = &spi_master_class;
+        master->cdev.dev = get_device(dev);
+        class_set_devdata(&master->cdev, &master[1]);
+
+        return master;
+}
+EXPORT_SYMBOL_GPL(spi_alloc_master);
+
+/**
+ * spi_register_master - register SPI master controller
+ * @master: initialized master, originally from spi_alloc_master()
+ *
+ * SPI master controllers connect to their drivers using some non-SPI bus,
+ * such as the platform bus.  The final stage of probe() in that code
+ * includes calling spi_register_master() to hook up to this SPI bus glue.
+ *
+ * SPI controllers use board specific (often SOC specific) bus numbers,
+ * and board-specific addressing for SPI devices combines those numbers
+ * with chip select numbers.  Since SPI does not directly support dynamic
+ * device identification, boards need configuration tables telling which
+ * chip is at which address.
+ *
+ * This must be called from context that can sleep.  It returns zero on
+ * success, else a negative error code (dropping the master's refcount).
+ */
+int __init_or_module
+spi_register_master(struct spi_master *master)
+{
+        static atomic_t         dyn_bus_id = ATOMIC_INIT(0);
+        struct device           *dev = master->cdev.dev;
+        int                     status = -ENODEV;
+        int                     dynamic = 0;
+
+        /* convention:  dynamically assigned bus IDs count down from the max */
+        if (master->bus_num == 0) {
+                master->bus_num = atomic_dec_return(&dyn_bus_id);
+                dynamic = 0;
+        }
+
+        /* register the device, then userspace will see it.
+         * registration fails if the bus ID is in use.
+         */
+        snprintf(master->cdev.class_id, sizeof master->cdev.class_id,
+                "spi%u", master->bus_num);
+        status = class_device_register(&master->cdev);
+        if (status < 0) {
+                class_device_put(&master->cdev);
+                goto done;
+        }
+        dev_dbg(dev, "registered master %s%s\n", master->cdev.class_id,
+                        dynamic ? " (dynamic)" : "");
+
+        /* populate children from any spi device tables */
+        scan_boardinfo(master);
+        status = 0;
+done:
+        return status;
+}
+EXPORT_SYMBOL_GPL(spi_register_master);
+
+
+static int __unregister(struct device *dev, void *unused)
+{
+        /* note: before about 2.6.14-rc1 this would corrupt memory: */
+        device_unregister(dev);
+        return 0;
+}
+
+/**
+ * spi_unregister_master - unregister SPI master controller
+ * @master: the master being unregistered
+ *
+ * This call is used only by SPI master controller drivers, which are the
+ * only ones directly touching chip registers.
+ *
+ * This must be called from context that can sleep.
+ */
+void spi_unregister_master(struct spi_master *master)
+{
+        class_device_unregister(&master->cdev);
+        (void) device_for_each_child(master->cdev.dev, NULL, __unregister);
+}
+EXPORT_SYMBOL_GPL(spi_unregister_master);
+
+/**
+ * spi_busnum_to_master - look up master associated with bus_num
+ * @bus_num: the master's bus number
+ *
+ * This call may be used with devices that are registered after
+ * arch init time.  It returns a refcounted pointer to the relevant
+ * spi_master (which the caller must release), or NULL if there is
+ * no such master registered.
+ */
+struct spi_master *spi_busnum_to_master(u16 bus_num)
+{
+        if (bus_num) {
+                char                    name[8];
+                struct kobject          *bus;
+
+                snprintf(name, sizeof name, "spi%u", bus_num);
+                bus = kset_find_obj(&spi_master_class.subsys.kset, name);
+                if (bus)
+                        return container_of(bus, struct spi_master, cdev.kobj);
+        }
+        return NULL;
+}
+EXPORT_SYMBOL_GPL(spi_busnum_to_master);
+
+
+/*-------------------------------------------------------------------------*/
+
+/**
+ * spi_sync - blocking/synchronous SPI data transfers
+ * @spi: device with which data will be exchanged
+ * @message: describes the data transfers
+ *
+ * This call may only be used from a context that may sleep.  The sleep
+ * is non-interruptible, and has no timeout.  Low-overhead controller
+ * drivers may DMA directly into and out of the message buffers.
+ *
+ * Note that the SPI device's chip select is active during the message,
+ * and then is normally disabled between messages.  Drivers for some
+ * frequently-used devices may want to minimize costs of selecting a chip,
+ * by leaving it selected in anticipation that the next message will go
+ * to the same chip.  (That may increase power usage.)
+ *
+ * The return value is a negative error code if the message could not be
+ * submitted, else zero.  When the value is zero, then message->status is
+ * also defined:  it's the completion code for the transfer, either zero
+ * or a negative error code from the controller driver.
+ */
+int spi_sync(struct spi_device *spi, struct spi_message *message)
+{
+        DECLARE_COMPLETION(done);
+        int status;
+
+        message->complete = (void (*)(void *)) complete;
+        message->context = &done;
+        status = spi_async(spi, message);
+        if (status == 0)
+                wait_for_completion(&done);
+        message->context = NULL;
+        return status;
+}
+EXPORT_SYMBOL_GPL(spi_sync);
+
+#define SPI_BUFSIZ      (SMP_CACHE_BYTES)
+
+static u8       *buf;
+
+/**
+ * spi_write_then_read - SPI synchronous write followed by read
+ * @spi: device with which data will be exchanged
+ * @txbuf: data to be written (need not be dma-safe)
+ * @n_tx: size of txbuf, in bytes
+ * @rxbuf: buffer into which data will be read
+ * @n_rx: size of rxbuf, in bytes (need not be dma-safe)
+ *
+ * This performs a half duplex MicroWire style transaction with the
+ * device, sending txbuf and then reading rxbuf.  The return value
+ * is zero for success, else a negative errno status code.
+ *
+ * Parameters to this routine are always copied using a small buffer,
+ * large transfers should use use spi_{async,sync}() calls with
+ * dma-safe buffers.
+ */
+int spi_write_then_read(struct spi_device *spi,
+                const u8 *txbuf, unsigned n_tx,
+                u8 *rxbuf, unsigned n_rx)
+{
+        static DECLARE_MUTEX(lock);
+
+        int                     status;
+        struct spi_message      message;
+        struct spi_transfer     x[2];
+        u8                      *local_buf;
+
+        /* Use preallocated DMA-safe buffer.  We can't avoid copying here,
+         * (as a pure convenience thing), but we can keep heap costs
+         * out of the hot path ...
+         */
+        if ((n_tx + n_rx) > SPI_BUFSIZ)
+                return -EINVAL;
+
+        /* ... unless someone else is using the pre-allocated buffer */
+        if (down_trylock(&lock)) {
+                local_buf = kmalloc(SPI_BUFSIZ, GFP_KERNEL);
+                if (!local_buf)
+                        return -ENOMEM;
+        } else
+                local_buf = buf;
+
+        memset(x, 0, sizeof x);
+
+        memcpy(local_buf, txbuf, n_tx);
+        x[0].tx_buf = local_buf;
+        x[0].len = n_tx;
+
+        x[1].rx_buf = local_buf + n_tx;
+        x[1].len = n_rx;
+
+        /* do the i/o */
+        message.transfers = x;
+        message.n_transfer = ARRAY_SIZE(x);
+        status = spi_sync(spi, &message);
+        if (status == 0) {
+                memcpy(rxbuf, x[1].rx_buf, n_rx);
+                status = message.status;
+        }
+
+        if (x[0].tx_buf == buf)
+                up(&lock);
+        else
+                kfree(local_buf);
+
+        return status;
+}
+EXPORT_SYMBOL_GPL(spi_write_then_read);
+
+/*-------------------------------------------------------------------------*/
+
+static int __init spi_init(void)
+{
+        buf = kmalloc(SPI_BUFSIZ, SLAB_KERNEL);
+        if (!buf)
+                return -ENOMEM;
+
+        bus_register(&spi_bus_type);
+        class_register(&spi_master_class);
+        return 0;
+}
+/* board_info is normally registered in arch_initcall(),
+ * but even essential drivers wait till later
+ */
+subsys_initcall(spi_init);
+