hwspinlock.txt: standardize document format
Each text file under Documentation follows a different format. Some doesn't even have titles! Change its representation to follow the adopted standard, using ReST markups for it to be parseable by Sphinx: - Adjust title markups; - remove explicit numeration from titles; - mark literal blocks as such; - replace _foo_ by **foo** for emphasis; - adjust whitespaces and add blank lines where needed. Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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Mauro Carvalho Chehab
Jonathan Corbet
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Коммит
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@ -1,6 +1,9 @@
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===========================
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Hardware Spinlock Framework
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===========================
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1. Introduction
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Introduction
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============
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Hardware spinlock modules provide hardware assistance for synchronization
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and mutual exclusion between heterogeneous processors and those not operating
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@ -32,286 +35,370 @@ structure).
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A common hwspinlock interface makes it possible to have generic, platform-
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independent, drivers.
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2. User API
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User API
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========
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::
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struct hwspinlock *hwspin_lock_request(void);
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- dynamically assign an hwspinlock and return its address, or NULL
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in case an unused hwspinlock isn't available. Users of this
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API will usually want to communicate the lock's id to the remote core
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before it can be used to achieve synchronization.
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Should be called from a process context (might sleep).
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Dynamically assign an hwspinlock and return its address, or NULL
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in case an unused hwspinlock isn't available. Users of this
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API will usually want to communicate the lock's id to the remote core
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before it can be used to achieve synchronization.
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Should be called from a process context (might sleep).
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::
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struct hwspinlock *hwspin_lock_request_specific(unsigned int id);
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- assign a specific hwspinlock id and return its address, or NULL
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if that hwspinlock is already in use. Usually board code will
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be calling this function in order to reserve specific hwspinlock
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ids for predefined purposes.
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Should be called from a process context (might sleep).
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Assign a specific hwspinlock id and return its address, or NULL
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if that hwspinlock is already in use. Usually board code will
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be calling this function in order to reserve specific hwspinlock
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ids for predefined purposes.
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Should be called from a process context (might sleep).
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::
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int of_hwspin_lock_get_id(struct device_node *np, int index);
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- retrieve the global lock id for an OF phandle-based specific lock.
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This function provides a means for DT users of a hwspinlock module
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to get the global lock id of a specific hwspinlock, so that it can
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be requested using the normal hwspin_lock_request_specific() API.
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The function returns a lock id number on success, -EPROBE_DEFER if
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the hwspinlock device is not yet registered with the core, or other
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error values.
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Should be called from a process context (might sleep).
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Retrieve the global lock id for an OF phandle-based specific lock.
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This function provides a means for DT users of a hwspinlock module
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to get the global lock id of a specific hwspinlock, so that it can
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be requested using the normal hwspin_lock_request_specific() API.
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The function returns a lock id number on success, -EPROBE_DEFER if
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the hwspinlock device is not yet registered with the core, or other
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error values.
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Should be called from a process context (might sleep).
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::
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int hwspin_lock_free(struct hwspinlock *hwlock);
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- free a previously-assigned hwspinlock; returns 0 on success, or an
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appropriate error code on failure (e.g. -EINVAL if the hwspinlock
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is already free).
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Should be called from a process context (might sleep).
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Free a previously-assigned hwspinlock; returns 0 on success, or an
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appropriate error code on failure (e.g. -EINVAL if the hwspinlock
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is already free).
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Should be called from a process context (might sleep).
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::
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int hwspin_lock_timeout(struct hwspinlock *hwlock, unsigned int timeout);
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- lock a previously-assigned hwspinlock with a timeout limit (specified in
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msecs). If the hwspinlock is already taken, the function will busy loop
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waiting for it to be released, but give up when the timeout elapses.
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Upon a successful return from this function, preemption is disabled so
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the caller must not sleep, and is advised to release the hwspinlock as
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soon as possible, in order to minimize remote cores polling on the
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hardware interconnect.
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Returns 0 when successful and an appropriate error code otherwise (most
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notably -ETIMEDOUT if the hwspinlock is still busy after timeout msecs).
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The function will never sleep.
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Lock a previously-assigned hwspinlock with a timeout limit (specified in
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msecs). If the hwspinlock is already taken, the function will busy loop
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waiting for it to be released, but give up when the timeout elapses.
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Upon a successful return from this function, preemption is disabled so
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the caller must not sleep, and is advised to release the hwspinlock as
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soon as possible, in order to minimize remote cores polling on the
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hardware interconnect.
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Returns 0 when successful and an appropriate error code otherwise (most
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notably -ETIMEDOUT if the hwspinlock is still busy after timeout msecs).
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The function will never sleep.
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::
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int hwspin_lock_timeout_irq(struct hwspinlock *hwlock, unsigned int timeout);
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- lock a previously-assigned hwspinlock with a timeout limit (specified in
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msecs). If the hwspinlock is already taken, the function will busy loop
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waiting for it to be released, but give up when the timeout elapses.
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Upon a successful return from this function, preemption and the local
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interrupts are disabled, so the caller must not sleep, and is advised to
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release the hwspinlock as soon as possible.
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Returns 0 when successful and an appropriate error code otherwise (most
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notably -ETIMEDOUT if the hwspinlock is still busy after timeout msecs).
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The function will never sleep.
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Lock a previously-assigned hwspinlock with a timeout limit (specified in
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msecs). If the hwspinlock is already taken, the function will busy loop
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waiting for it to be released, but give up when the timeout elapses.
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Upon a successful return from this function, preemption and the local
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interrupts are disabled, so the caller must not sleep, and is advised to
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release the hwspinlock as soon as possible.
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Returns 0 when successful and an appropriate error code otherwise (most
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notably -ETIMEDOUT if the hwspinlock is still busy after timeout msecs).
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The function will never sleep.
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::
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int hwspin_lock_timeout_irqsave(struct hwspinlock *hwlock, unsigned int to,
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unsigned long *flags);
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- lock a previously-assigned hwspinlock with a timeout limit (specified in
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msecs). If the hwspinlock is already taken, the function will busy loop
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waiting for it to be released, but give up when the timeout elapses.
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Upon a successful return from this function, preemption is disabled,
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local interrupts are disabled and their previous state is saved at the
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given flags placeholder. The caller must not sleep, and is advised to
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release the hwspinlock as soon as possible.
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Returns 0 when successful and an appropriate error code otherwise (most
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notably -ETIMEDOUT if the hwspinlock is still busy after timeout msecs).
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The function will never sleep.
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unsigned long *flags);
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Lock a previously-assigned hwspinlock with a timeout limit (specified in
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msecs). If the hwspinlock is already taken, the function will busy loop
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waiting for it to be released, but give up when the timeout elapses.
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Upon a successful return from this function, preemption is disabled,
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local interrupts are disabled and their previous state is saved at the
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given flags placeholder. The caller must not sleep, and is advised to
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release the hwspinlock as soon as possible.
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Returns 0 when successful and an appropriate error code otherwise (most
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notably -ETIMEDOUT if the hwspinlock is still busy after timeout msecs).
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The function will never sleep.
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::
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int hwspin_trylock(struct hwspinlock *hwlock);
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- attempt to lock a previously-assigned hwspinlock, but immediately fail if
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it is already taken.
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Upon a successful return from this function, preemption is disabled so
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caller must not sleep, and is advised to release the hwspinlock as soon as
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possible, in order to minimize remote cores polling on the hardware
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interconnect.
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Returns 0 on success and an appropriate error code otherwise (most
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notably -EBUSY if the hwspinlock was already taken).
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The function will never sleep.
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Attempt to lock a previously-assigned hwspinlock, but immediately fail if
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it is already taken.
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Upon a successful return from this function, preemption is disabled so
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caller must not sleep, and is advised to release the hwspinlock as soon as
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possible, in order to minimize remote cores polling on the hardware
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interconnect.
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Returns 0 on success and an appropriate error code otherwise (most
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notably -EBUSY if the hwspinlock was already taken).
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The function will never sleep.
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::
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int hwspin_trylock_irq(struct hwspinlock *hwlock);
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- attempt to lock a previously-assigned hwspinlock, but immediately fail if
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it is already taken.
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Upon a successful return from this function, preemption and the local
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interrupts are disabled so caller must not sleep, and is advised to
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release the hwspinlock as soon as possible.
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Returns 0 on success and an appropriate error code otherwise (most
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notably -EBUSY if the hwspinlock was already taken).
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The function will never sleep.
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Attempt to lock a previously-assigned hwspinlock, but immediately fail if
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it is already taken.
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Upon a successful return from this function, preemption and the local
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interrupts are disabled so caller must not sleep, and is advised to
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release the hwspinlock as soon as possible.
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Returns 0 on success and an appropriate error code otherwise (most
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notably -EBUSY if the hwspinlock was already taken).
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The function will never sleep.
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::
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int hwspin_trylock_irqsave(struct hwspinlock *hwlock, unsigned long *flags);
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- attempt to lock a previously-assigned hwspinlock, but immediately fail if
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it is already taken.
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Upon a successful return from this function, preemption is disabled,
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the local interrupts are disabled and their previous state is saved
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at the given flags placeholder. The caller must not sleep, and is advised
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to release the hwspinlock as soon as possible.
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Returns 0 on success and an appropriate error code otherwise (most
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notably -EBUSY if the hwspinlock was already taken).
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The function will never sleep.
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Attempt to lock a previously-assigned hwspinlock, but immediately fail if
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it is already taken.
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Upon a successful return from this function, preemption is disabled,
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the local interrupts are disabled and their previous state is saved
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at the given flags placeholder. The caller must not sleep, and is advised
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to release the hwspinlock as soon as possible.
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Returns 0 on success and an appropriate error code otherwise (most
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notably -EBUSY if the hwspinlock was already taken).
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The function will never sleep.
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::
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void hwspin_unlock(struct hwspinlock *hwlock);
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- unlock a previously-locked hwspinlock. Always succeed, and can be called
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from any context (the function never sleeps). Note: code should _never_
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unlock an hwspinlock which is already unlocked (there is no protection
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against this).
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Unlock a previously-locked hwspinlock. Always succeed, and can be called
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from any context (the function never sleeps).
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.. note::
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code should **never** unlock an hwspinlock which is already unlocked
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(there is no protection against this).
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::
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void hwspin_unlock_irq(struct hwspinlock *hwlock);
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- unlock a previously-locked hwspinlock and enable local interrupts.
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The caller should _never_ unlock an hwspinlock which is already unlocked.
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Doing so is considered a bug (there is no protection against this).
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Upon a successful return from this function, preemption and local
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interrupts are enabled. This function will never sleep.
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Unlock a previously-locked hwspinlock and enable local interrupts.
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The caller should **never** unlock an hwspinlock which is already unlocked.
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Doing so is considered a bug (there is no protection against this).
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Upon a successful return from this function, preemption and local
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interrupts are enabled. This function will never sleep.
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::
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void
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hwspin_unlock_irqrestore(struct hwspinlock *hwlock, unsigned long *flags);
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- unlock a previously-locked hwspinlock.
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The caller should _never_ unlock an hwspinlock which is already unlocked.
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Doing so is considered a bug (there is no protection against this).
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Upon a successful return from this function, preemption is reenabled,
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and the state of the local interrupts is restored to the state saved at
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the given flags. This function will never sleep.
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Unlock a previously-locked hwspinlock.
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The caller should **never** unlock an hwspinlock which is already unlocked.
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Doing so is considered a bug (there is no protection against this).
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Upon a successful return from this function, preemption is reenabled,
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and the state of the local interrupts is restored to the state saved at
|
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the given flags. This function will never sleep.
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::
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int hwspin_lock_get_id(struct hwspinlock *hwlock);
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- retrieve id number of a given hwspinlock. This is needed when an
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hwspinlock is dynamically assigned: before it can be used to achieve
|
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mutual exclusion with a remote cpu, the id number should be communicated
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to the remote task with which we want to synchronize.
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Returns the hwspinlock id number, or -EINVAL if hwlock is null.
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3. Typical usage
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Retrieve id number of a given hwspinlock. This is needed when an
|
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hwspinlock is dynamically assigned: before it can be used to achieve
|
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mutual exclusion with a remote cpu, the id number should be communicated
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to the remote task with which we want to synchronize.
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#include <linux/hwspinlock.h>
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#include <linux/err.h>
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Returns the hwspinlock id number, or -EINVAL if hwlock is null.
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int hwspinlock_example1(void)
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{
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struct hwspinlock *hwlock;
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int ret;
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Typical usage
|
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=============
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/* dynamically assign a hwspinlock */
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hwlock = hwspin_lock_request();
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if (!hwlock)
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...
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::
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id = hwspin_lock_get_id(hwlock);
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/* probably need to communicate id to a remote processor now */
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#include <linux/hwspinlock.h>
|
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#include <linux/err.h>
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|
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/* take the lock, spin for 1 sec if it's already taken */
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||||
ret = hwspin_lock_timeout(hwlock, 1000);
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if (ret)
|
||||
...
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int hwspinlock_example1(void)
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{
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struct hwspinlock *hwlock;
|
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int ret;
|
||||
|
||||
/*
|
||||
* we took the lock, do our thing now, but do NOT sleep
|
||||
*/
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/* dynamically assign a hwspinlock */
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hwlock = hwspin_lock_request();
|
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if (!hwlock)
|
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...
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/* release the lock */
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hwspin_unlock(hwlock);
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id = hwspin_lock_get_id(hwlock);
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||||
/* probably need to communicate id to a remote processor now */
|
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|
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/* free the lock */
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ret = hwspin_lock_free(hwlock);
|
||||
if (ret)
|
||||
...
|
||||
/* take the lock, spin for 1 sec if it's already taken */
|
||||
ret = hwspin_lock_timeout(hwlock, 1000);
|
||||
if (ret)
|
||||
...
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||||
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||||
return ret;
|
||||
}
|
||||
/*
|
||||
* we took the lock, do our thing now, but do NOT sleep
|
||||
*/
|
||||
|
||||
int hwspinlock_example2(void)
|
||||
{
|
||||
struct hwspinlock *hwlock;
|
||||
int ret;
|
||||
/* release the lock */
|
||||
hwspin_unlock(hwlock);
|
||||
|
||||
/*
|
||||
* assign a specific hwspinlock id - this should be called early
|
||||
* by board init code.
|
||||
*/
|
||||
hwlock = hwspin_lock_request_specific(PREDEFINED_LOCK_ID);
|
||||
if (!hwlock)
|
||||
...
|
||||
/* free the lock */
|
||||
ret = hwspin_lock_free(hwlock);
|
||||
if (ret)
|
||||
...
|
||||
|
||||
/* 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;
|
||||
return ret;
|
||||
}
|
||||
|
||||
/*
|
||||
* we took the lock, do our thing now, but do NOT sleep
|
||||
*/
|
||||
int hwspinlock_example2(void)
|
||||
{
|
||||
struct hwspinlock *hwlock;
|
||||
int ret;
|
||||
|
||||
/* release the lock */
|
||||
hwspin_unlock(hwlock);
|
||||
/*
|
||||
* assign a specific hwspinlock id - this should be called early
|
||||
* by board init code.
|
||||
*/
|
||||
hwlock = hwspin_lock_request_specific(PREDEFINED_LOCK_ID);
|
||||
if (!hwlock)
|
||||
...
|
||||
|
||||
/* free the lock */
|
||||
ret = hwspin_lock_free(hwlock);
|
||||
if (ret)
|
||||
...
|
||||
/* 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;
|
||||
}
|
||||
|
||||
return 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;
|
||||
}
|
||||
|
||||
|
||||
4. API for implementors
|
||||
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:
|
||||
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;
|
||||
};
|
||||
/**
|
||||
* 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.
|
||||
|
|
|
|||
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