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hwspinlock.txt: standardize document format

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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>
This commit is contained in:
Mauro Carvalho Chehab 2017-05-14 14:23:08 -03:00 committed by Jonathan Corbet
parent 440e4f6d29
commit e2862b25dc
1 changed files with 292 additions and 205 deletions
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Documentation/hwspinlock.txt
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@ -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
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.
#include <linux/hwspinlock.h>
#include <linux/err.h>
Returns the hwspinlock id number, or -EINVAL if hwlock is null.
int hwspinlock_example1(void)
{
struct hwspinlock *hwlock;
int ret;
Typical usage
=============
/* 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 */
#include <linux/hwspinlock.h>
#include <linux/err.h>
/* take the lock, spin for 1 sec if it's already taken */
ret = hwspin_lock_timeout(hwlock, 1000);
if (ret)
...
int hwspinlock_example1(void)
{
struct hwspinlock *hwlock;
int ret;
/*
* we took the lock, do our thing now, but do NOT sleep
*/
/* dynamically assign a hwspinlock */
hwlock = hwspin_lock_request();
if (!hwlock)
...
/* release the lock */
hwspin_unlock(hwlock);
id = hwspin_lock_get_id(hwlock);
/* probably need to communicate id to a remote processor now */
/* free the lock */
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)
...
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.