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From cf32b71e981ca63e8f349d8585ca2a3583b556e0 Mon Sep 17 00:00:00 2001
From: Ernst Schwab <eschwab@online.de>
Date: Mon, 28 Jun 2010 17:49:29 -0700
Subject: [PATCH] spi/mmc_spi: SPI bus locking API, using mutex
SPI bus locking API to allow exclusive access to the SPI bus, especially, but
not limited to, for the mmc_spi driver.
Coded according to an outline from Grant Likely; here is his
specification (accidentally swapped function names corrected):
It requires 3 things to be added to struct spi_master.
- 1 Mutex
- 1 spin lock
- 1 flag.
The mutex protects spi_sync, and provides sleeping "for free"
The spinlock protects the atomic spi_async call.
The flag is set when the lock is obtained, and checked while holding
the spinlock in spi_async(). If the flag is checked, then spi_async()
must fail immediately.
The current runtime API looks like this:
spi_async(struct spi_device*, struct spi_message*);
spi_sync(struct spi_device*, struct spi_message*);
The API needs to be extended to this:
spi_async(struct spi_device*, struct spi_message*)
spi_sync(struct spi_device*, struct spi_message*)
spi_bus_lock(struct spi_master*) /* although struct spi_device* might
be easier */
spi_bus_unlock(struct spi_master*)
spi_async_locked(struct spi_device*, struct spi_message*)
spi_sync_locked(struct spi_device*, struct spi_message*)
Drivers can only call the last two if they already hold the spi_master_lock().
spi_bus_lock() obtains the mutex, obtains the spin lock, sets the
flag, and releases the spin lock before returning. It doesn't even
need to sleep while waiting for "in-flight" spi_transactions to
complete because its purpose is to guarantee no additional
transactions are added. It does not guarantee that the bus is idle.
spi_bus_unlock() clears the flag and releases the mutex, which will
wake up any waiters.
The difference between spi_async() and spi_async_locked() is that the
locked version bypasses the check of the lock flag. Both versions
need to obtain the spinlock.
The difference between spi_sync() and spi_sync_locked() is that
spi_sync() must hold the mutex while enqueuing a new transfer.
spi_sync_locked() doesn't because the mutex is already held. Note
however that spi_sync must *not* continue to hold the mutex while
waiting for the transfer to complete, otherwise only one transfer
could be queued up at a time!
Almost no code needs to be written. The current spi_async() and
spi_sync() can probably be renamed to __spi_async() and __spi_sync()
so that spi_async(), spi_sync(), spi_async_locked() and
spi_sync_locked() can just become wrappers around the common code.
spi_sync() is protected by a mutex because it can sleep
spi_async() needs to be protected with a flag and a spinlock because
it can be called atomically and must not sleep
Signed-off-by: Ernst Schwab <eschwab@online.de>
[grant.likely@secretlab.ca: use spin_lock_irqsave()]
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Tested-by: Matt Fleming <matt@console-pimps.org>
Tested-by: Antonio Ospite <ospite@studenti.unina.it>
---
drivers/spi/spi.c | 225 ++++++++++++++++++++++++++++++++++++++++-------
include/linux/spi/spi.h | 12 +++
2 files changed, 204 insertions(+), 33 deletions(-)
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -524,6 +524,10 @@ int spi_register_master(struct spi_maste
dynamic = 1;
}
+ spin_lock_init(&master->bus_lock_spinlock);
+ mutex_init(&master->bus_lock_mutex);
+ master->bus_lock_flag = 0;
+
/* register the device, then userspace will see it.
* registration fails if the bus ID is in use.
*/
@@ -663,6 +667,35 @@ int spi_setup(struct spi_device *spi)
}
EXPORT_SYMBOL_GPL(spi_setup);
+static int __spi_async(struct spi_device *spi, struct spi_message *message)
+{
+ struct spi_master *master = spi->master;
+
+ /* Half-duplex links include original MicroWire, and ones with
+ * only one data pin like SPI_3WIRE (switches direction) or where
+ * either MOSI or MISO is missing. They can also be caused by
+ * software limitations.
+ */
+ if ((master->flags & SPI_MASTER_HALF_DUPLEX)
+ || (spi->mode & SPI_3WIRE)) {
+ struct spi_transfer *xfer;
+ unsigned flags = master->flags;
+
+ list_for_each_entry(xfer, &message->transfers, transfer_list) {
+ if (xfer->rx_buf && xfer->tx_buf)
+ return -EINVAL;
+ if ((flags & SPI_MASTER_NO_TX) && xfer->tx_buf)
+ return -EINVAL;
+ if ((flags & SPI_MASTER_NO_RX) && xfer->rx_buf)
+ return -EINVAL;
+ }
+ }
+
+ message->spi = spi;
+ message->status = -EINPROGRESS;
+ return master->transfer(spi, message);
+}
+
/**
* spi_async - asynchronous SPI transfer
* @spi: device with which data will be exchanged
@@ -695,33 +728,68 @@ EXPORT_SYMBOL_GPL(spi_setup);
int spi_async(struct spi_device *spi, struct spi_message *message)
{
struct spi_master *master = spi->master;
+ int ret;
+ unsigned long flags;
- /* Half-duplex links include original MicroWire, and ones with
- * only one data pin like SPI_3WIRE (switches direction) or where
- * either MOSI or MISO is missing. They can also be caused by
- * software limitations.
- */
- if ((master->flags & SPI_MASTER_HALF_DUPLEX)
- || (spi->mode & SPI_3WIRE)) {
- struct spi_transfer *xfer;
- unsigned flags = master->flags;
+ spin_lock_irqsave(&master->bus_lock_spinlock, flags);
- list_for_each_entry(xfer, &message->transfers, transfer_list) {
- if (xfer->rx_buf && xfer->tx_buf)
- return -EINVAL;
- if ((flags & SPI_MASTER_NO_TX) && xfer->tx_buf)
- return -EINVAL;
- if ((flags & SPI_MASTER_NO_RX) && xfer->rx_buf)
- return -EINVAL;
- }
- }
+ if (master->bus_lock_flag)
+ ret = -EBUSY;
+ else
+ ret = __spi_async(spi, message);
- message->spi = spi;
- message->status = -EINPROGRESS;
- return master->transfer(spi, message);
+ spin_unlock_irqrestore(&master->bus_lock_spinlock, flags);
+
+ return ret;
}
EXPORT_SYMBOL_GPL(spi_async);
+/**
+ * spi_async_locked - version of spi_async with exclusive bus usage
+ * @spi: device with which data will be exchanged
+ * @message: describes the data transfers, including completion callback
+ * Context: any (irqs may be blocked, etc)
+ *
+ * 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. After that
+ * callback returns, the driver which issued the transfer request may
+ * deallocate the associated memory; it's no longer in use by any SPI
+ * core or controller driver 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.
+ *
+ * On detection of any fault during the transfer, processing of
+ * the entire message is aborted, and the device is deselected.
+ * Until returning from the associated message completion callback,
+ * no other spi_message queued to that device will be processed.
+ * (This rule applies equally to all the synchronous transfer calls,
+ * which are wrappers around this core asynchronous primitive.)
+ */
+int spi_async_locked(struct spi_device *spi, struct spi_message *message)
+{
+ struct spi_master *master = spi->master;
+ int ret;
+ unsigned long flags;
+
+ spin_lock_irqsave(&master->bus_lock_spinlock, flags);
+
+ ret = __spi_async(spi, message);
+
+ spin_unlock_irqrestore(&master->bus_lock_spinlock, flags);
+
+ return ret;
+
+}
+EXPORT_SYMBOL_GPL(spi_async_locked);
+
/*-------------------------------------------------------------------------*/
@@ -735,6 +803,32 @@ static void spi_complete(void *arg)
complete(arg);
}
+static int __spi_sync(struct spi_device *spi, struct spi_message *message,
+ int bus_locked)
+{
+ DECLARE_COMPLETION_ONSTACK(done);
+ int status;
+ struct spi_master *master = spi->master;
+
+ message->complete = spi_complete;
+ message->context = &done;
+
+ if (!bus_locked)
+ mutex_lock(&master->bus_lock_mutex);
+
+ status = spi_async_locked(spi, message);
+
+ if (!bus_locked)
+ mutex_unlock(&master->bus_lock_mutex);
+
+ if (status == 0) {
+ wait_for_completion(&done);
+ status = message->status;
+ }
+ message->context = NULL;
+ return status;
+}
+
/**
* spi_sync - blocking/synchronous SPI data transfers
* @spi: device with which data will be exchanged
@@ -758,21 +852,86 @@ static void spi_complete(void *arg)
*/
int spi_sync(struct spi_device *spi, struct spi_message *message)
{
- DECLARE_COMPLETION_ONSTACK(done);
- int status;
-
- message->complete = spi_complete;
- message->context = &done;
- status = spi_async(spi, message);
- if (status == 0) {
- wait_for_completion(&done);
- status = message->status;
- }
- message->context = NULL;
- return status;
+ return __spi_sync(spi, message, 0);
}
EXPORT_SYMBOL_GPL(spi_sync);
+/**
+ * spi_sync_locked - version of spi_sync with exclusive bus usage
+ * @spi: device with which data will be exchanged
+ * @message: describes the data transfers
+ * Context: can sleep
+ *
+ * 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.
+ *
+ * This call should be used by drivers that require exclusive access to the
+ * SPI bus. It has to be preceeded by a spi_bus_lock call. The SPI bus must
+ * be released by a spi_bus_unlock call when the exclusive access is over.
+ *
+ * It returns zero on success, else a negative error code.
+ */
+int spi_sync_locked(struct spi_device *spi, struct spi_message *message)
+{
+ return __spi_sync(spi, message, 1);
+}
+EXPORT_SYMBOL_GPL(spi_sync_locked);
+
+/**
+ * spi_bus_lock - obtain a lock for exclusive SPI bus usage
+ * @master: SPI bus master that should be locked for exclusive bus access
+ * Context: can sleep
+ *
+ * This call may only be used from a context that may sleep. The sleep
+ * is non-interruptible, and has no timeout.
+ *
+ * This call should be used by drivers that require exclusive access to the
+ * SPI bus. The SPI bus must be released by a spi_bus_unlock call when the
+ * exclusive access is over. Data transfer must be done by spi_sync_locked
+ * and spi_async_locked calls when the SPI bus lock is held.
+ *
+ * It returns zero on success, else a negative error code.
+ */
+int spi_bus_lock(struct spi_master *master)
+{
+ unsigned long flags;
+
+ mutex_lock(&master->bus_lock_mutex);
+
+ spin_lock_irqsave(&master->bus_lock_spinlock, flags);
+ master->bus_lock_flag = 1;
+ spin_unlock_irqrestore(&master->bus_lock_spinlock, flags);
+
+ /* mutex remains locked until spi_bus_unlock is called */
+
+ return 0;
+}
+EXPORT_SYMBOL_GPL(spi_bus_lock);
+
+/**
+ * spi_bus_unlock - release the lock for exclusive SPI bus usage
+ * @master: SPI bus master that was locked for exclusive bus access
+ * Context: can sleep
+ *
+ * This call may only be used from a context that may sleep. The sleep
+ * is non-interruptible, and has no timeout.
+ *
+ * This call releases an SPI bus lock previously obtained by an spi_bus_lock
+ * call.
+ *
+ * It returns zero on success, else a negative error code.
+ */
+int spi_bus_unlock(struct spi_master *master)
+{
+ master->bus_lock_flag = 0;
+
+ mutex_unlock(&master->bus_lock_mutex);
+
+ return 0;
+}
+EXPORT_SYMBOL_GPL(spi_bus_unlock);
+
/* portable code must never pass more than 32 bytes */
#define SPI_BUFSIZ max(32,SMP_CACHE_BYTES)
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -261,6 +261,13 @@ struct spi_master {
#define SPI_MASTER_NO_RX BIT(1) /* can't do buffer read */
#define SPI_MASTER_NO_TX BIT(2) /* can't do buffer write */
+ /* lock and mutex for SPI bus locking */
+ spinlock_t bus_lock_spinlock;
+ struct mutex bus_lock_mutex;
+
+ /* flag indicating that the SPI bus is locked for exclusive use */
+ bool bus_lock_flag;
+
/* Setup mode and clock, etc (spi driver may call many times).
*
* IMPORTANT: this may be called when transfers to another
@@ -541,6 +548,8 @@ static inline void spi_message_free(stru
extern int spi_setup(struct spi_device *spi);
extern int spi_async(struct spi_device *spi, struct spi_message *message);
+extern int spi_async_locked(struct spi_device *spi,
+ struct spi_message *message);
/*---------------------------------------------------------------------------*/
@@ -550,6 +559,9 @@ extern int spi_async(struct spi_device *
*/
extern int spi_sync(struct spi_device *spi, struct spi_message *message);
+extern int spi_sync_locked(struct spi_device *spi, struct spi_message *message);
+extern int spi_bus_lock(struct spi_master *master);
+extern int spi_bus_unlock(struct spi_master *master);
/**
* spi_write - SPI synchronous write
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