[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>

1 files changed, 542 insertions, 0 deletions

diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
new file mode 100644
index 000000000000..51a6769114df
--- /dev/null
+++ b/include/linux/spi/spi.h
@@ -0,0 +1,542 @@
+/*
+ * 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.
+ */
+
+#ifndef __LINUX_SPI_H
+#define __LINUX_SPI_H
+
+/*
+ * INTERFACES between SPI master drivers and infrastructure
+ * (There's no SPI slave support for Linux yet...)
+ *
+ * A "struct device_driver" for an spi_device uses "spi_bus_type" and
+ * needs no special API wrappers (much like platform_bus).  These drivers
+ * are bound to devices based on their names (much like platform_bus),
+ * and are available in dev->driver.
+ */
+extern struct bus_type spi_bus_type;
+
+/**
+ * struct spi_device - Master side proxy for an SPI slave device
+ * @dev: Driver model representation of the device.
+ * @master: SPI controller used with the device.
+ * @max_speed_hz: Maximum clock rate to be used with this chip
+ *      (on this board); may be changed by the device's driver.
+ * @chip-select: Chipselect, distinguishing chips handled by "master".
+ * @mode: The spi mode defines how data is clocked out and in.
+ *      This may be changed by the device's driver.
+ * @bits_per_word: Data transfers involve one or more words; word sizes
+ *      like eight or 12 bits are common.  In-memory wordsizes are
+ *      powers of two bytes (e.g. 20 bit samples use 32 bits).
+ *      This may be changed by the device's driver.
+ * @irq: Negative, or the number passed to request_irq() to receive
+ *      interrupts from this device.
+ * @controller_state: Controller's runtime state
+ * @controller_data: Static board-specific definitions for controller, such
+ *      as FIFO initialization parameters; from board_info.controller_data
+ *
+ * An spi_device is used to interchange data between an SPI slave
+ * (usually a discrete chip) and CPU memory.
+ *
+ * In "dev", the platform_data is used to hold information about this
+ * device that's meaningful to the device's protocol driver, but not
+ * to its controller.  One example might be an identifier for a chip
+ * variant with slightly different functionality.
+ */
+struct spi_device {
+        struct device           dev;
+        struct spi_master       *master;
+        u32                     max_speed_hz;
+        u8                      chip_select;
+        u8                      mode;
+#define SPI_CPHA        0x01            /* clock phase */
+#define SPI_CPOL        0x02            /* clock polarity */
+#define SPI_MODE_0      (0|0)
+#define SPI_MODE_1      (0|SPI_CPHA)
+#define SPI_MODE_2      (SPI_CPOL|0)
+#define SPI_MODE_3      (SPI_CPOL|SPI_CPHA)
+#define SPI_CS_HIGH     0x04            /* chipselect active high? */
+        u8                      bits_per_word;
+        int                     irq;
+        void                    *controller_state;
+        const void              *controller_data;
+        const char              *modalias;
+
+        // likely need more hooks for more protocol options affecting how
+        // the controller talks to its chips, like:
+        //  - bit order (default is wordwise msb-first)
+        //  - memory packing (12 bit samples into low bits, others zeroed)
+        //  - priority
+        //  - chipselect delays
+        //  - ...
+};
+
+static inline struct spi_device *to_spi_device(struct device *dev)
+{
+        return container_of(dev, struct spi_device, dev);
+}
+
+/* most drivers won't need to care about device refcounting */
+static inline struct spi_device *spi_dev_get(struct spi_device *spi)
+{
+        return (spi && get_device(&spi->dev)) ? spi : NULL;
+}
+
+static inline void spi_dev_put(struct spi_device *spi)
+{
+        if (spi)
+                put_device(&spi->dev);
+}
+
+/* ctldata is for the bus_master driver's runtime state */
+static inline void *spi_get_ctldata(struct spi_device *spi)
+{
+        return spi->controller_state;
+}
+
+static inline void spi_set_ctldata(struct spi_device *spi, void *state)
+{
+        spi->controller_state = state;
+}
+
+
+struct spi_message;
+
+
+/**
+ * struct spi_master - interface to SPI master controller
+ * @cdev: class interface to this driver
+ * @bus_num: board-specific (and often SOC-specific) identifier for a
+ *      given SPI controller.
+ * @num_chipselects: chipselects are used to distinguish individual
+ *      SPI slaves, and are numbered from zero to num_chipselects.
+ *      each slave has a chipselect signal, but it's common that not
+ *      every chipselect is connected to a slave.
+ * @setup: updates the device mode and clocking records used by a
+ *      device's SPI controller; protocol code may call this.
+ * @transfer: adds a message to the controller's transfer queue.
+ * @cleanup: frees controller-specific state
+ *
+ * Each SPI master controller can communicate with one or more spi_device
+ * children.  These make a small bus, sharing MOSI, MISO and SCK signals
+ * but not chip select signals.  Each device may be configured to use a
+ * different clock rate, since those shared signals are ignored unless
+ * the chip is selected.
+ *
+ * The driver for an SPI controller manages access to those devices through
+ * a queue of spi_message transactions, copyin data between CPU memory and
+ * an SPI slave device).  For each such message it queues, it calls the
+ * message's completion function when the transaction completes.
+ */
+struct spi_master {
+        struct class_device     cdev;
+
+        /* other than zero (== assign one dynamically), bus_num is fully
+         * board-specific.  usually that simplifies to being SOC-specific.
+         * example:  one SOC has three SPI controllers, numbered 1..3,
+         * and one board's schematics might show it using SPI-2.  software
+         * would normally use bus_num=2 for that controller.
+         */
+        u16                     bus_num;
+
+        /* chipselects will be integral to many controllers; some others
+         * might use board-specific GPIOs.
+         */
+        u16                     num_chipselect;
+
+        /* setup mode and clock, etc (spi driver may call many times) */
+        int                     (*setup)(struct spi_device *spi);
+
+        /* bidirectional bulk transfers
+         *
+         * + The transfer() method may not sleep; its main role is
+         *   just to add the message to the queue.
+         * + For now there's no remove-from-queue operation, or
+         *   any other request management
+         * + To a given spi_device, message queueing is pure fifo
+         *
+         * + The master's main job is to process its message queue,
+         *   selecting a chip then transferring data
+         * + If there are multiple spi_device children, the i/o queue
+         *   arbitration algorithm is unspecified (round robin, fifo,
+         *   priority, reservations, preemption, etc)
+         *
+         * + Chipselect stays active during the entire message
+         *   (unless modified by spi_transfer.cs_change != 0).
+         * + The message transfers use clock and SPI mode parameters
+         *   previously established by setup() for this device
+         */
+        int                     (*transfer)(struct spi_device *spi,
+                                                struct spi_message *mesg);
+
+        /* called on release() to free memory provided by spi_master */
+        void                    (*cleanup)(const struct spi_device *spi);
+};
+
+/* the spi driver core manages memory for the spi_master classdev */
+extern struct spi_master *
+spi_alloc_master(struct device *host, unsigned size);
+
+extern int spi_register_master(struct spi_master *master);
+extern void spi_unregister_master(struct spi_master *master);
+
+extern struct spi_master *spi_busnum_to_master(u16 busnum);
+
+/*---------------------------------------------------------------------------*/
+
+/*
+ * I/O INTERFACE between SPI controller and protocol drivers
+ *
+ * Protocol drivers use a queue of spi_messages, each transferring data
+ * between the controller and memory buffers.
+ *
+ * The spi_messages themselves consist of a series of read+write transfer
+ * segments.  Those segments always read the same number of bits as they
+ * write; but one or the other is easily ignored by passing a null buffer
+ * pointer.  (This is unlike most types of I/O API, because SPI hardware
+ * is full duplex.)
+ *
+ * NOTE:  Allocation of spi_transfer and spi_message memory is entirely
+ * up to the protocol driver, which guarantees the integrity of both (as
+ * well as the data buffers) for as long as the message is queued.
+ */
+
+/**
+ * struct spi_transfer - a read/write buffer pair
+ * @tx_buf: data to be written (dma-safe address), or NULL
+ * @rx_buf: data to be read (dma-safe address), or NULL
+ * @tx_dma: DMA address of buffer, if spi_message.is_dma_mapped
+ * @rx_dma: DMA address of buffer, if spi_message.is_dma_mapped
+ * @len: size of rx and tx buffers (in bytes)
+ * @cs_change: affects chipselect after this transfer completes
+ * @delay_usecs: microseconds to delay after this transfer before
+ *      (optionally) changing the chipselect status, then starting
+ *      the next transfer or completing this spi_message.
+ *
+ * SPI transfers always write the same number of bytes as they read.
+ * Protocol drivers should always provide rx_buf and/or tx_buf.
+ * In some cases, they may also want to provide DMA addresses for
+ * the data being transferred; that may reduce overhead, when the
+ * underlying driver uses dma.
+ *
+ * All SPI transfers start with the relevant chipselect active.  Drivers
+ * can change behavior of the chipselect after the transfer finishes
+ * (including any mandatory delay).  The normal behavior is to leave it
+ * selected, except for the last transfer in a message.  Setting cs_change
+ * allows two additional behavior options:
+ *
+ * (i) If the transfer isn't the last one in the message, this flag is
+ * used to make the chipselect briefly go inactive in the middle of the
+ * message.  Toggling chipselect in this way may be needed to terminate
+ * a chip command, letting a single spi_message perform all of group of
+ * chip transactions together.
+ *
+ * (ii) When the transfer is the last one in the message, the chip may
+ * stay selected until the next transfer.  This is purely a performance
+ * hint; the controller driver may need to select a different device
+ * for the next message.
+ */
+struct spi_transfer {
+        /* it's ok if tx_buf == rx_buf (right?)
+         * for MicroWire, one buffer must be null
+         * buffers must work with dma_*map_single() calls
+         */
+        const void      *tx_buf;
+        void            *rx_buf;
+        unsigned        len;
+
+        dma_addr_t      tx_dma;
+        dma_addr_t      rx_dma;
+
+        unsigned        cs_change:1;
+        u16             delay_usecs;
+};
+
+/**
+ * struct spi_message - one multi-segment SPI transaction
+ * @transfers: the segements of the transaction
+ * @n_transfer: how many segments
+ * @spi: SPI device to which the transaction is queued
+ * @is_dma_mapped: if true, the caller provided both dma and cpu virtual
+ *      addresses for each transfer buffer
+ * @complete: called to report transaction completions
+ * @context: the argument to complete() when it's called
+ * @actual_length: how many bytes were transferd
+ * @status: zero for success, else negative errno
+ * @queue: for use by whichever driver currently owns the message
+ * @state: for use by whichever driver currently owns the message
+ */
+struct spi_message {
+        struct spi_transfer     *transfers;
+        unsigned                n_transfer;
+
+        struct spi_device       *spi;
+
+        unsigned                is_dma_mapped:1;
+
+        /* REVISIT:  we might want a flag affecting the behavior of the
+         * last transfer ... allowing things like "read 16 bit length L"
+         * immediately followed by "read L bytes".  Basically imposing
+         * a specific message scheduling algorithm.
+         *
+         * Some controller drivers (message-at-a-time queue processing)
+         * could provide that as their default scheduling algorithm.  But
+         * others (with multi-message pipelines) would need a flag to
+         * tell them about such special cases.
+         */
+
+        /* completion is reported through a callback */
+        void                    FASTCALL((*complete)(void *context));
+        void                    *context;
+        unsigned                actual_length;
+        int                     status;
+
+        /* for optional use by whatever driver currently owns the
+         * spi_message ...  between calls to spi_async and then later
+         * complete(), that's the spi_master controller driver.
+         */
+        struct list_head        queue;
+        void                    *state;
+};
+
+/**
+ * spi_setup -- setup SPI mode and clock rate
+ * @spi: the device whose settings are being modified
+ *
+ * SPI protocol drivers may need to update the transfer mode if the
+ * device doesn't work with the mode 0 default.  They may likewise need
+ * to update clock rates or word sizes from initial values.  This function
+ * changes those settings, and must be called from a context that can sleep.
+ */
+static inline int
+spi_setup(struct spi_device *spi)
+{
+        return spi->master->setup(spi);
+}
+
+
+/**
+ * spi_async -- asynchronous SPI transfer
+ * @spi: device with which data will be exchanged
+ * @message: describes the data transfers, including completion callback
+ *
+ * This call may be used in_irq and other contexts which can't sleep,
+ * as well as from task contexts which can sleep.
+ *
+ * The completion callback is invoked in a context which can't sleep.
+ * Before that invocation, the value of message->status is undefined.
+ * When the callback is issued, message->status holds either zero (to
+ * indicate complete success) or a negative error code.
+ *
+ * Note that although all messages to a spi_device are handled in
+ * FIFO order, messages may go to different devices in other orders.
+ * Some device might be higher priority, or have various "hard" access
+ * time requirements, for example.
+ */
+static inline int
+spi_async(struct spi_device *spi, struct spi_message *message)
+{
+        message->spi = spi;
+        return spi->master->transfer(spi, message);
+}
+
+/*---------------------------------------------------------------------------*/
+
+/* All these synchronous SPI transfer routines are utilities layered
+ * over the core async transfer primitive.  Here, "synchronous" means
+ * they will sleep uninterruptibly until the async transfer completes.
+ */
+
+extern int spi_sync(struct spi_device *spi, struct spi_message *message);
+
+/**
+ * spi_write - SPI synchronous write
+ * @spi: device to which data will be written
+ * @buf: data buffer
+ * @len: data buffer size
+ *
+ * This writes the buffer and returns zero or a negative error code.
+ * Callable only from contexts that can sleep.
+ */
+static inline int
+spi_write(struct spi_device *spi, const u8 *buf, size_t len)
+{
+        struct spi_transfer     t = {
+                        .tx_buf         = buf,
+                        .rx_buf         = NULL,
+                        .len            = len,
+                        .cs_change      = 0,
+                };
+        struct spi_message      m = {
+                        .transfers      = &t,
+                        .n_transfer     = 1,
+                };
+
+        return spi_sync(spi, &m);
+}
+
+/**
+ * spi_read - SPI synchronous read
+ * @spi: device from which data will be read
+ * @buf: data buffer
+ * @len: data buffer size
+ *
+ * This writes the buffer and returns zero or a negative error code.
+ * Callable only from contexts that can sleep.
+ */
+static inline int
+spi_read(struct spi_device *spi, u8 *buf, size_t len)
+{
+        struct spi_transfer     t = {
+                        .tx_buf         = NULL,
+                        .rx_buf         = buf,
+                        .len            = len,
+                        .cs_change      = 0,
+                };
+        struct spi_message      m = {
+                        .transfers      = &t,
+                        .n_transfer     = 1,
+                };
+
+        return spi_sync(spi, &m);
+}
+
+extern int spi_write_then_read(struct spi_device *spi,
+                const u8 *txbuf, unsigned n_tx,
+                u8 *rxbuf, unsigned n_rx);
+
+/**
+ * spi_w8r8 - SPI synchronous 8 bit write followed by 8 bit read
+ * @spi: device with which data will be exchanged
+ * @cmd: command to be written before data is read back
+ *
+ * This returns the (unsigned) eight bit number returned by the
+ * device, or else a negative error code.  Callable only from
+ * contexts that can sleep.
+ */
+static inline ssize_t spi_w8r8(struct spi_device *spi, u8 cmd)
+{
+        ssize_t                 status;
+        u8                      result;
+
+        status = spi_write_then_read(spi, &cmd, 1, &result, 1);
+
+        /* return negative errno or unsigned value */
+        return (status < 0) ? status : result;
+}
+
+/**
+ * spi_w8r16 - SPI synchronous 8 bit write followed by 16 bit read
+ * @spi: device with which data will be exchanged
+ * @cmd: command to be written before data is read back
+ *
+ * This returns the (unsigned) sixteen bit number returned by the
+ * device, or else a negative error code.  Callable only from
+ * contexts that can sleep.
+ *
+ * The number is returned in wire-order, which is at least sometimes
+ * big-endian.
+ */
+static inline ssize_t spi_w8r16(struct spi_device *spi, u8 cmd)
+{
+        ssize_t                 status;
+        u16                     result;
+
+        status = spi_write_then_read(spi, &cmd, 1, (u8 *) &result, 2);
+
+        /* return negative errno or unsigned value */
+        return (status < 0) ? status : result;
+}
+
+/*---------------------------------------------------------------------------*/
+
+/*
+ * INTERFACE between board init code and SPI infrastructure.
+ *
+ * No SPI driver ever sees these SPI device table segments, but
+ * it's how the SPI core (or adapters that get hotplugged) grows
+ * the driver model tree.
+ *
+ * As a rule, SPI devices can't be probed.  Instead, board init code
+ * provides a table listing the devices which are present, with enough
+ * information to bind and set up the device's driver.  There's basic
+ * support for nonstatic configurations too; enough to handle adding
+ * parport adapters, or microcontrollers acting as USB-to-SPI bridges.
+ */
+
+/* board-specific information about each SPI device */
+struct spi_board_info {
+        /* the device name and module name are coupled, like platform_bus;
+         * "modalias" is normally the driver name.
+         *
+         * platform_data goes to spi_device.dev.platform_data,
+         * controller_data goes to spi_device.platform_data,
+         * irq is copied too
+         */
+        char            modalias[KOBJ_NAME_LEN];
+        const void      *platform_data;
+        const void      *controller_data;
+        int             irq;
+
+        /* slower signaling on noisy or low voltage boards */
+        u32             max_speed_hz;
+
+
+        /* bus_num is board specific and matches the bus_num of some
+         * spi_master that will probably be registered later.
+         *
+         * chip_select reflects how this chip is wired to that master;
+         * it's less than num_chipselect.
+         */
+        u16             bus_num;
+        u16             chip_select;
+
+        /* ... may need additional spi_device chip config data here.
+         * avoid stuff protocol drivers can set; but include stuff
+         * needed to behave without being bound to a driver:
+         *  - chipselect polarity
+         *  - quirks like clock rate mattering when not selected
+         */
+};
+
+#ifdef  CONFIG_SPI
+extern int
+spi_register_board_info(struct spi_board_info const *info, unsigned n);
+#else
+/* board init code may ignore whether SPI is configured or not */
+static inline int
+spi_register_board_info(struct spi_board_info const *info, unsigned n)
+        { return 0; }
+#endif
+
+
+/* If you're hotplugging an adapter with devices (parport, usb, etc)
+ * use spi_new_device() to describe each device.  You can also call
+ * spi_unregister_device() to get start making that device vanish,
+ * but normally that would be handled by spi_unregister_master().
+ */
+extern struct spi_device *
+spi_new_device(struct spi_master *, struct spi_board_info *);
+
+static inline void
+spi_unregister_device(struct spi_device *spi)
+{
+        if (spi)
+                device_unregister(&spi->dev);
+}
+
+#endif /* __LINUX_SPI_H */