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| -rw-r--r-- | Documentation/hwspinlock.txt | 527 |
1 files changed, 307 insertions, 220 deletions
diff --git a/Documentation/hwspinlock.txt b/Documentation/hwspinlock.txt index 61c1ee98e59f..ed640a278185 100644 --- a/Documentation/hwspinlock.txt +++ b/Documentation/hwspinlock.txt @@ -1,6 +1,9 @@ +=========================== Hardware Spinlock Framework +=========================== -1. Introduction +Introduction +============ Hardware spinlock modules provide hardware assistance for synchronization and mutual exclusion between heterogeneous processors and those not operating @@ -32,286 +35,370 @@ structure). 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. |