generic: bacport SPI bus locking API

SVN-Revision: 22862

1 files changed, 382 insertions, 0 deletions

diff --git a/target/linux/generic/patches-2.6.34/910-backport-spi-bus-locking-api.patch b/target/linux/generic/patches-2.6.34/910-backport-spi-bus-locking-api.patch
new file mode 100644
index 0000000000..dbf3e51b4d
--- /dev/null
+++ b/target/linux/generic/patches-2.6.34/910-backport-spi-bus-locking-api.patch
@@ -0,0 +1,382 @@
+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
+@@ -527,6 +527,10 @@ 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.
+ 	 */
+@@ -666,6 +670,35 @@ 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
+@@ -698,33 +731,68 @@ 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);
++
+ 
+ /*-------------------------------------------------------------------------*/
+ 
+@@ -738,6 +806,32 @@ 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
+@@ -761,21 +855,86 @@ 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
+@@ -262,6 +262,13 @@ 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
+@@ -542,6 +549,8 @@ 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);
+ 
+ /*---------------------------------------------------------------------------*/
+ 
+@@ -551,6 +560,9 @@ 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