+===========================
Hardware Spinlock Framework
+===========================
-1. Introduction
+Introduction
+============
Hardware spinlock modules provide hardware assistance for synchronization
and mutual exclusion between heterogeneous processors and those not operating
A common hwspinlock interface makes it possible to have generic, platform-
independent, drivers.
-2. User API
+User API
+========
+
+::
struct hwspinlock *hwspin_lock_request(void);
- - dynamically assign an hwspinlock and return its address, or NULL
- in case an unused hwspinlock isn't available. Users of this
- API will usually want to communicate the lock's id to the remote core
- before it can be used to achieve synchronization.
- Should be called from a process context (might sleep).
+
+Dynamically assign an hwspinlock and return its address, or NULL
+in case an unused hwspinlock isn't available. Users of this
+API will usually want to communicate the lock's id to the remote core
+before it can be used to achieve synchronization.
+
+Should be called from a process context (might sleep).
+
+::
struct hwspinlock *hwspin_lock_request_specific(unsigned int id);
- - assign a specific hwspinlock id and return its address, or NULL
- if that hwspinlock is already in use. Usually board code will
- be calling this function in order to reserve specific hwspinlock
- ids for predefined purposes.
- Should be called from a process context (might sleep).
+
+Assign a specific hwspinlock id and return its address, or NULL
+if that hwspinlock is already in use. Usually board code will
+be calling this function in order to reserve specific hwspinlock
+ids for predefined purposes.
+
+Should be called from a process context (might sleep).
+
+::
int of_hwspin_lock_get_id(struct device_node *np, int index);
- - retrieve the global lock id for an OF phandle-based specific lock.
- This function provides a means for DT users of a hwspinlock module
- to get the global lock id of a specific hwspinlock, so that it can
- be requested using the normal hwspin_lock_request_specific() API.
- The function returns a lock id number on success, -EPROBE_DEFER if
- the hwspinlock device is not yet registered with the core, or other
- error values.
- Should be called from a process context (might sleep).
+
+Retrieve the global lock id for an OF phandle-based specific lock.
+This function provides a means for DT users of a hwspinlock module
+to get the global lock id of a specific hwspinlock, so that it can
+be requested using the normal hwspin_lock_request_specific() API.
+
+The function returns a lock id number on success, -EPROBE_DEFER if
+the hwspinlock device is not yet registered with the core, or other
+error values.
+
+Should be called from a process context (might sleep).
+
+::
int hwspin_lock_free(struct hwspinlock *hwlock);
- - free a previously-assigned hwspinlock; returns 0 on success, or an
- appropriate error code on failure (e.g. -EINVAL if the hwspinlock
- is already free).
- Should be called from a process context (might sleep).
+
+Free a previously-assigned hwspinlock; returns 0 on success, or an
+appropriate error code on failure (e.g. -EINVAL if the hwspinlock
+is already free).
+
+Should be called from a process context (might sleep).
+
+::
int hwspin_lock_timeout(struct hwspinlock *hwlock, unsigned int timeout);
- - lock a previously-assigned hwspinlock with a timeout limit (specified in
- msecs). If the hwspinlock is already taken, the function will busy loop
- waiting for it to be released, but give up when the timeout elapses.
- Upon a successful return from this function, preemption is disabled so
- the caller must not sleep, and is advised to release the hwspinlock as
- soon as possible, in order to minimize remote cores polling on the
- hardware interconnect.
- Returns 0 when successful and an appropriate error code otherwise (most
- notably -ETIMEDOUT if the hwspinlock is still busy after timeout msecs).
- The function will never sleep.
+
+Lock a previously-assigned hwspinlock with a timeout limit (specified in
+msecs). If the hwspinlock is already taken, the function will busy loop
+waiting for it to be released, but give up when the timeout elapses.
+Upon a successful return from this function, preemption is disabled so
+the caller must not sleep, and is advised to release the hwspinlock as
+soon as possible, in order to minimize remote cores polling on the
+hardware interconnect.
+
+Returns 0 when successful and an appropriate error code otherwise (most
+notably -ETIMEDOUT if the hwspinlock is still busy after timeout msecs).
+The function will never sleep.
+
+::
int hwspin_lock_timeout_irq(struct hwspinlock *hwlock, unsigned int timeout);
- - lock a previously-assigned hwspinlock with a timeout limit (specified in
- msecs). If the hwspinlock is already taken, the function will busy loop
- waiting for it to be released, but give up when the timeout elapses.
- Upon a successful return from this function, preemption and the local
- interrupts are disabled, so the caller must not sleep, and is advised to
- release the hwspinlock as soon as possible.
- Returns 0 when successful and an appropriate error code otherwise (most
- notably -ETIMEDOUT if the hwspinlock is still busy after timeout msecs).
- The function will never sleep.
+
+Lock a previously-assigned hwspinlock with a timeout limit (specified in
+msecs). If the hwspinlock is already taken, the function will busy loop
+waiting for it to be released, but give up when the timeout elapses.
+Upon a successful return from this function, preemption and the local
+interrupts are disabled, so the caller must not sleep, and is advised to
+release the hwspinlock as soon as possible.
+
+Returns 0 when successful and an appropriate error code otherwise (most
+notably -ETIMEDOUT if the hwspinlock is still busy after timeout msecs).
+The function will never sleep.
+
+::
int hwspin_lock_timeout_irqsave(struct hwspinlock *hwlock, unsigned int to,
- unsigned long *flags);
- - lock a previously-assigned hwspinlock with a timeout limit (specified in
- msecs). If the hwspinlock is already taken, the function will busy loop
- waiting for it to be released, but give up when the timeout elapses.
- Upon a successful return from this function, preemption is disabled,
- local interrupts are disabled and their previous state is saved at the
- given flags placeholder. The caller must not sleep, and is advised to
- release the hwspinlock as soon as possible.
- Returns 0 when successful and an appropriate error code otherwise (most
- notably -ETIMEDOUT if the hwspinlock is still busy after timeout msecs).
- The function will never sleep.
+ unsigned long *flags);
+
+Lock a previously-assigned hwspinlock with a timeout limit (specified in
+msecs). If the hwspinlock is already taken, the function will busy loop
+waiting for it to be released, but give up when the timeout elapses.
+Upon a successful return from this function, preemption is disabled,
+local interrupts are disabled and their previous state is saved at the
+given flags placeholder. The caller must not sleep, and is advised to
+release the hwspinlock as soon as possible.
+
+Returns 0 when successful and an appropriate error code otherwise (most
+notably -ETIMEDOUT if the hwspinlock is still busy after timeout msecs).
+
+The function will never sleep.
+
+::
int hwspin_trylock(struct hwspinlock *hwlock);
- - attempt to lock a previously-assigned hwspinlock, but immediately fail if
- it is already taken.
- Upon a successful return from this function, preemption is disabled so
- caller must not sleep, and is advised to release the hwspinlock as soon as
- possible, in order to minimize remote cores polling on the hardware
- interconnect.
- Returns 0 on success and an appropriate error code otherwise (most
- notably -EBUSY if the hwspinlock was already taken).
- The function will never sleep.
+
+
+Attempt to lock a previously-assigned hwspinlock, but immediately fail if
+it is already taken.
+
+Upon a successful return from this function, preemption is disabled so
+caller must not sleep, and is advised to release the hwspinlock as soon as
+possible, in order to minimize remote cores polling on the hardware
+interconnect.
+
+Returns 0 on success and an appropriate error code otherwise (most
+notably -EBUSY if the hwspinlock was already taken).
+The function will never sleep.
+
+::
int hwspin_trylock_irq(struct hwspinlock *hwlock);
- - attempt to lock a previously-assigned hwspinlock, but immediately fail if
- it is already taken.
- Upon a successful return from this function, preemption and the local
- interrupts are disabled so caller must not sleep, and is advised to
- release the hwspinlock as soon as possible.
- Returns 0 on success and an appropriate error code otherwise (most
- notably -EBUSY if the hwspinlock was already taken).
- The function will never sleep.
+
+
+Attempt to lock a previously-assigned hwspinlock, but immediately fail if
+it is already taken.
+
+Upon a successful return from this function, preemption and the local
+interrupts are disabled so caller must not sleep, and is advised to
+release the hwspinlock as soon as possible.
+
+Returns 0 on success and an appropriate error code otherwise (most
+notably -EBUSY if the hwspinlock was already taken).
+
+The function will never sleep.
+
+::
int hwspin_trylock_irqsave(struct hwspinlock *hwlock, unsigned long *flags);
- - attempt to lock a previously-assigned hwspinlock, but immediately fail if
- it is already taken.
- Upon a successful return from this function, preemption is disabled,
- the local interrupts are disabled and their previous state is saved
- at the given flags placeholder. The caller must not sleep, and is advised
- to release the hwspinlock as soon as possible.
- Returns 0 on success and an appropriate error code otherwise (most
- notably -EBUSY if the hwspinlock was already taken).
- The function will never sleep.
+
+Attempt to lock a previously-assigned hwspinlock, but immediately fail if
+it is already taken.
+
+Upon a successful return from this function, preemption is disabled,
+the local interrupts are disabled and their previous state is saved
+at the given flags placeholder. The caller must not sleep, and is advised
+to release the hwspinlock as soon as possible.
+
+Returns 0 on success and an appropriate error code otherwise (most
+notably -EBUSY if the hwspinlock was already taken).
+The function will never sleep.
+
+::
void hwspin_unlock(struct hwspinlock *hwlock);
- - unlock a previously-locked hwspinlock. Always succeed, and can be called
- from any context (the function never sleeps). Note: code should _never_
- unlock an hwspinlock which is already unlocked (there is no protection
- against this).
+
+Unlock a previously-locked hwspinlock. Always succeed, and can be called
+from any context (the function never sleeps).
+
+.. note::
+
+ code should **never** unlock an hwspinlock which is already unlocked
+ (there is no protection against this).
+
+::
void hwspin_unlock_irq(struct hwspinlock *hwlock);
- - unlock a previously-locked hwspinlock and enable local interrupts.
- The caller should _never_ unlock an hwspinlock which is already unlocked.
- Doing so is considered a bug (there is no protection against this).
- Upon a successful return from this function, preemption and local
- interrupts are enabled. This function will never sleep.
+
+Unlock a previously-locked hwspinlock and enable local interrupts.
+The caller should **never** unlock an hwspinlock which is already unlocked.
+
+Doing so is considered a bug (there is no protection against this).
+Upon a successful return from this function, preemption and local
+interrupts are enabled. This function will never sleep.
+
+::
void
hwspin_unlock_irqrestore(struct hwspinlock *hwlock, unsigned long *flags);
- - unlock a previously-locked hwspinlock.
- The caller should _never_ unlock an hwspinlock which is already unlocked.
- Doing so is considered a bug (there is no protection against this).
- Upon a successful return from this function, preemption is reenabled,
- and the state of the local interrupts is restored to the state saved at
- the given flags. This function will never sleep.
+
+Unlock a previously-locked hwspinlock.
+
+The caller should **never** unlock an hwspinlock which is already unlocked.
+Doing so is considered a bug (there is no protection against this).
+Upon a successful return from this function, preemption is reenabled,
+and the state of the local interrupts is restored to the state saved at
+the given flags. This function will never sleep.
+
+::
int hwspin_lock_get_id(struct hwspinlock *hwlock);
- - retrieve id number of a given hwspinlock. This is needed when an
- hwspinlock is dynamically assigned: before it can be used to achieve
- mutual exclusion with a remote cpu, the id number should be communicated
- to the remote task with which we want to synchronize.
- Returns the hwspinlock id number, or -EINVAL if hwlock is null.
-
-3. Typical usage
-
-#include <linux/hwspinlock.h>
-#include <linux/err.h>
-
-int hwspinlock_example1(void)
-{
- struct hwspinlock *hwlock;
- int ret;
-
- /* dynamically assign a hwspinlock */
- hwlock = hwspin_lock_request();
- if (!hwlock)
- ...
-
- id = hwspin_lock_get_id(hwlock);
- /* probably need to communicate id to a remote processor now */
-
- /* take the lock, spin for 1 sec if it's already taken */
- ret = hwspin_lock_timeout(hwlock, 1000);
- if (ret)
- ...
-
- /*
- * we took the lock, do our thing now, but do NOT sleep
- */
-
- /* release the lock */
- hwspin_unlock(hwlock);
-
- /* free the lock */
- ret = hwspin_lock_free(hwlock);
- if (ret)
- ...
-
- return ret;
-}
-
-int hwspinlock_example2(void)
-{
- struct hwspinlock *hwlock;
- int ret;
-
- /*
- * assign a specific hwspinlock id - this should be called early
- * by board init code.
- */
- hwlock = hwspin_lock_request_specific(PREDEFINED_LOCK_ID);
- if (!hwlock)
- ...
-
- /* try to take it, but don't spin on it */
- ret = hwspin_trylock(hwlock);
- if (!ret) {
- pr_info("lock is already taken\n");
- return -EBUSY;
- }
- /*
- * we took the lock, do our thing now, but do NOT sleep
- */
+Retrieve id number of a given hwspinlock. This is needed when an
+hwspinlock is dynamically assigned: before it can be used to achieve
+mutual exclusion with a remote cpu, the id number should be communicated
+to the remote task with which we want to synchronize.
+
+Returns the hwspinlock id number, or -EINVAL if hwlock is null.
+
+Typical usage
+=============
- /* release the lock */
- hwspin_unlock(hwlock);
+::
- /* free the lock */
- ret = hwspin_lock_free(hwlock);
- if (ret)
- ...
+ #include <linux/hwspinlock.h>
+ #include <linux/err.h>
- return ret;
-}
+ int hwspinlock_example1(void)
+ {
+ struct hwspinlock *hwlock;
+ int ret;
+ /* dynamically assign a hwspinlock */
+ hwlock = hwspin_lock_request();
+ if (!hwlock)
+ ...
-4. API for implementors
+ id = hwspin_lock_get_id(hwlock);
+ /* probably need to communicate id to a remote processor now */
+
+ /* take the lock, spin for 1 sec if it's already taken */
+ ret = hwspin_lock_timeout(hwlock, 1000);
+ if (ret)
+ ...
+
+ /*
+ * we took the lock, do our thing now, but do NOT sleep
+ */
+
+ /* release the lock */
+ hwspin_unlock(hwlock);
+
+ /* free the lock */
+ ret = hwspin_lock_free(hwlock);
+ if (ret)
+ ...
+
+ return ret;
+ }
+
+ int hwspinlock_example2(void)
+ {
+ struct hwspinlock *hwlock;
+ int ret;
+
+ /*
+ * assign a specific hwspinlock id - this should be called early
+ * by board init code.
+ */
+ hwlock = hwspin_lock_request_specific(PREDEFINED_LOCK_ID);
+ if (!hwlock)
+ ...
+
+ /* try to take it, but don't spin on it */
+ ret = hwspin_trylock(hwlock);
+ if (!ret) {
+ pr_info("lock is already taken\n");
+ return -EBUSY;
+ }
+
+ /*
+ * we took the lock, do our thing now, but do NOT sleep
+ */
+
+ /* release the lock */
+ hwspin_unlock(hwlock);
+
+ /* free the lock */
+ ret = hwspin_lock_free(hwlock);
+ if (ret)
+ ...
+
+ return ret;
+ }
+
+
+API for implementors
+====================
+
+::
int hwspin_lock_register(struct hwspinlock_device *bank, struct device *dev,
const struct hwspinlock_ops *ops, int base_id, int num_locks);
- - to be called from the underlying platform-specific implementation, in
- order to register a new hwspinlock device (which is usually a bank of
- numerous locks). Should be called from a process context (this function
- might sleep).
- Returns 0 on success, or appropriate error code on failure.
+
+To be called from the underlying platform-specific implementation, in
+order to register a new hwspinlock device (which is usually a bank of
+numerous locks). Should be called from a process context (this function
+might sleep).
+
+Returns 0 on success, or appropriate error code on failure.
+
+::
int hwspin_lock_unregister(struct hwspinlock_device *bank);
- - to be called from the underlying vendor-specific implementation, in order
- to unregister an hwspinlock device (which is usually a bank of numerous
- locks).
- Should be called from a process context (this function might sleep).
- Returns the address of hwspinlock on success, or NULL on error (e.g.
- if the hwspinlock is still in use).
-5. Important structs
+To be called from the underlying vendor-specific implementation, in order
+to unregister an hwspinlock device (which is usually a bank of numerous
+locks).
+
+Should be called from a process context (this function might sleep).
+
+Returns the address of hwspinlock on success, or NULL on error (e.g.
+if the hwspinlock is still in use).
+
+Important structs
+=================
struct hwspinlock_device is a device which usually contains a bank
of hardware locks. It is registered by the underlying hwspinlock
implementation using the hwspin_lock_register() API.
-/**
- * struct hwspinlock_device - a device which usually spans numerous hwspinlocks
- * @dev: underlying device, will be used to invoke runtime PM api
- * @ops: platform-specific hwspinlock handlers
- * @base_id: id index of the first lock in this device
- * @num_locks: number of locks in this device
- * @lock: dynamically allocated array of 'struct hwspinlock'
- */
-struct hwspinlock_device {
- struct device *dev;
- const struct hwspinlock_ops *ops;
- int base_id;
- int num_locks;
- struct hwspinlock lock[0];
-};
+::
+
+ /**
+ * struct hwspinlock_device - a device which usually spans numerous hwspinlocks
+ * @dev: underlying device, will be used to invoke runtime PM api
+ * @ops: platform-specific hwspinlock handlers
+ * @base_id: id index of the first lock in this device
+ * @num_locks: number of locks in this device
+ * @lock: dynamically allocated array of 'struct hwspinlock'
+ */
+ struct hwspinlock_device {
+ struct device *dev;
+ const struct hwspinlock_ops *ops;
+ int base_id;
+ int num_locks;
+ struct hwspinlock lock[0];
+ };
struct hwspinlock_device contains an array of hwspinlock structs, each
-of which represents a single hardware lock:
-
-/**
- * struct hwspinlock - this struct represents a single hwspinlock instance
- * @bank: the hwspinlock_device structure which owns this lock
- * @lock: initialized and used by hwspinlock core
- * @priv: private data, owned by the underlying platform-specific hwspinlock drv
- */
-struct hwspinlock {
- struct hwspinlock_device *bank;
- spinlock_t lock;
- void *priv;
-};
+of which represents a single hardware lock::
+
+ /**
+ * struct hwspinlock - this struct represents a single hwspinlock instance
+ * @bank: the hwspinlock_device structure which owns this lock
+ * @lock: initialized and used by hwspinlock core
+ * @priv: private data, owned by the underlying platform-specific hwspinlock drv
+ */
+ struct hwspinlock {
+ struct hwspinlock_device *bank;
+ spinlock_t lock;
+ void *priv;
+ };
When registering a bank of locks, the hwspinlock driver only needs to
set the priv members of the locks. The rest of the members are set and
initialized by the hwspinlock core itself.
-6. Implementation callbacks
+Implementation callbacks
+========================
-There are three possible callbacks defined in 'struct hwspinlock_ops':
+There are three possible callbacks defined in 'struct hwspinlock_ops'::
-struct hwspinlock_ops {
- int (*trylock)(struct hwspinlock *lock);
- void (*unlock)(struct hwspinlock *lock);
- void (*relax)(struct hwspinlock *lock);
-};
+ struct hwspinlock_ops {
+ int (*trylock)(struct hwspinlock *lock);
+ void (*unlock)(struct hwspinlock *lock);
+ void (*relax)(struct hwspinlock *lock);
+ };
The first two callbacks are mandatory:
The ->trylock() callback should make a single attempt to take the lock, and
-return 0 on failure and 1 on success. This callback may _not_ sleep.
+return 0 on failure and 1 on success. This callback may **not** sleep.
The ->unlock() callback releases the lock. It always succeed, and it, too,
-may _not_ sleep.
+may **not** sleep.
The ->relax() callback is optional. It is called by hwspinlock core while
spinning on a lock, and can be used by the underlying implementation to force
-a delay between two successive invocations of ->trylock(). It may _not_ sleep.
+a delay between two successive invocations of ->trylock(). It may **not** sleep.
projects / openwrt / staging / blogic.git / commitdiff