Commit e2862b25 authored by Mauro Carvalho Chehab's avatar Mauro Carvalho Chehab Committed by Jonathan Corbet
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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;
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Signed-off-by: default avatarMauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: default avatarJonathan Corbet <corbet@lwn.net>
parent 440e4f6d
===========================
Hardware Spinlock Framework Hardware Spinlock Framework
===========================
1. Introduction Introduction
============
Hardware spinlock modules provide hardware assistance for synchronization Hardware spinlock modules provide hardware assistance for synchronization
and mutual exclusion between heterogeneous processors and those not operating and mutual exclusion between heterogeneous processors and those not operating
...@@ -32,142 +35,212 @@ structure). ...@@ -32,142 +35,212 @@ structure).
A common hwspinlock interface makes it possible to have generic, platform- A common hwspinlock interface makes it possible to have generic, platform-
independent, drivers. independent, drivers.
2. User API User API
========
::
struct hwspinlock *hwspin_lock_request(void); 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 Dynamically assign an hwspinlock and return its address, or NULL
API will usually want to communicate the lock's id to the remote core in case an unused hwspinlock isn't available. Users of this
before it can be used to achieve synchronization. API will usually want to communicate the lock's id to the remote core
Should be called from a process context (might sleep). 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); 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 Assign a specific hwspinlock id and return its address, or NULL
be calling this function in order to reserve specific hwspinlock if that hwspinlock is already in use. Usually board code will
ids for predefined purposes. be calling this function in order to reserve specific hwspinlock
Should be called from a process context (might sleep). 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); 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 Retrieve the global lock id for an OF phandle-based specific lock.
to get the global lock id of a specific hwspinlock, so that it can This function provides a means for DT users of a hwspinlock module
be requested using the normal hwspin_lock_request_specific() API. to get the global lock id of a specific hwspinlock, so that it can
The function returns a lock id number on success, -EPROBE_DEFER if be requested using the normal hwspin_lock_request_specific() API.
the hwspinlock device is not yet registered with the core, or other
error values. The function returns a lock id number on success, -EPROBE_DEFER if
Should be called from a process context (might sleep). 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); 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 Free a previously-assigned hwspinlock; returns 0 on success, or an
is already free). appropriate error code on failure (e.g. -EINVAL if the hwspinlock
Should be called from a process context (might sleep). is already free).
Should be called from a process context (might sleep).
::
int hwspin_lock_timeout(struct hwspinlock *hwlock, unsigned int timeout); 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 Lock a previously-assigned hwspinlock with a timeout limit (specified in
waiting for it to be released, but give up when the timeout elapses. msecs). If the hwspinlock is already taken, the function will busy loop
Upon a successful return from this function, preemption is disabled so waiting for it to be released, but give up when the timeout elapses.
the caller must not sleep, and is advised to release the hwspinlock as Upon a successful return from this function, preemption is disabled so
soon as possible, in order to minimize remote cores polling on the the caller must not sleep, and is advised to release the hwspinlock as
hardware interconnect. soon as possible, in order to minimize remote cores polling on the
Returns 0 when successful and an appropriate error code otherwise (most hardware interconnect.
notably -ETIMEDOUT if the hwspinlock is still busy after timeout msecs).
The function will never sleep. 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); 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 Lock a previously-assigned hwspinlock with a timeout limit (specified in
waiting for it to be released, but give up when the timeout elapses. msecs). If the hwspinlock is already taken, the function will busy loop
Upon a successful return from this function, preemption and the local waiting for it to be released, but give up when the timeout elapses.
interrupts are disabled, so the caller must not sleep, and is advised to Upon a successful return from this function, preemption and the local
release the hwspinlock as soon as possible. interrupts are disabled, so the caller must not sleep, and is advised to
Returns 0 when successful and an appropriate error code otherwise (most release the hwspinlock as soon as possible.
notably -ETIMEDOUT if the hwspinlock is still busy after timeout msecs).
The function will never sleep. 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, int hwspin_lock_timeout_irqsave(struct hwspinlock *hwlock, unsigned int to,
unsigned long *flags); 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 Lock a previously-assigned hwspinlock with a timeout limit (specified in
waiting for it to be released, but give up when the timeout elapses. msecs). If the hwspinlock is already taken, the function will busy loop
Upon a successful return from this function, preemption is disabled, waiting for it to be released, but give up when the timeout elapses.
local interrupts are disabled and their previous state is saved at the Upon a successful return from this function, preemption is disabled,
given flags placeholder. The caller must not sleep, and is advised to local interrupts are disabled and their previous state is saved at the
release the hwspinlock as soon as possible. given flags placeholder. The caller must not sleep, and is advised to
Returns 0 when successful and an appropriate error code otherwise (most release the hwspinlock as soon as possible.
notably -ETIMEDOUT if the hwspinlock is still busy after timeout msecs).
The function will never sleep. 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); 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 Attempt to lock a previously-assigned hwspinlock, but immediately fail if
caller must not sleep, and is advised to release the hwspinlock as soon as it is already taken.
possible, in order to minimize remote cores polling on the hardware
interconnect. Upon a successful return from this function, preemption is disabled so
Returns 0 on success and an appropriate error code otherwise (most caller must not sleep, and is advised to release the hwspinlock as soon as
notably -EBUSY if the hwspinlock was already taken). possible, in order to minimize remote cores polling on the hardware
The function will never sleep. 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); 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 Attempt to lock a previously-assigned hwspinlock, but immediately fail if
interrupts are disabled so caller must not sleep, and is advised to it is already taken.
release the hwspinlock as soon as possible.
Returns 0 on success and an appropriate error code otherwise (most Upon a successful return from this function, preemption and the local
notably -EBUSY if the hwspinlock was already taken). interrupts are disabled so caller must not sleep, and is advised to
The function will never sleep. 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); 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. Attempt to lock a previously-assigned hwspinlock, but immediately fail if
Upon a successful return from this function, preemption is disabled, it is already taken.
the local interrupts are disabled and their previous state is saved
at the given flags placeholder. The caller must not sleep, and is advised Upon a successful return from this function, preemption is disabled,
to release the hwspinlock as soon as possible. the local interrupts are disabled and their previous state is saved
Returns 0 on success and an appropriate error code otherwise (most at the given flags placeholder. The caller must not sleep, and is advised
notably -EBUSY if the hwspinlock was already taken). to release the hwspinlock as soon as possible.
The function will never sleep.
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); 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 a previously-locked hwspinlock. Always succeed, and can be called
unlock an hwspinlock which is already unlocked (there is no protection from any context (the function never sleeps).
against this).
.. note::
code should **never** unlock an hwspinlock which is already unlocked
(there is no protection against this).
::
void hwspin_unlock_irq(struct hwspinlock *hwlock); 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. Unlock a previously-locked hwspinlock and enable local interrupts.
Doing so is considered a bug (there is no protection against this). The caller should **never** unlock an hwspinlock which is already unlocked.
Upon a successful return from this function, preemption and local
interrupts are enabled. This function will never sleep. 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 void
hwspin_unlock_irqrestore(struct hwspinlock *hwlock, unsigned long *flags); 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. Unlock a previously-locked hwspinlock.
Doing so is considered a bug (there is no protection against this).
Upon a successful return from this function, preemption is reenabled, The caller should **never** unlock an hwspinlock which is already unlocked.
and the state of the local interrupts is restored to the state saved at Doing so is considered a bug (there is no protection against this).
the given flags. This function will never sleep. 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); 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.
Returns the hwspinlock id number, or -EINVAL if hwlock is null.
Typical usage
=============
#include <linux/hwspinlock.h> ::
#include <linux/err.h>
int hwspinlock_example1(void) #include <linux/hwspinlock.h>
{ #include <linux/err.h>
int hwspinlock_example1(void)
{
struct hwspinlock *hwlock; struct hwspinlock *hwlock;
int ret; int ret;
...@@ -197,10 +270,10 @@ int hwspinlock_example1(void) ...@@ -197,10 +270,10 @@ int hwspinlock_example1(void)
... ...
return ret; return ret;
} }
int hwspinlock_example2(void) int hwspinlock_example2(void)
{ {
struct hwspinlock *hwlock; struct hwspinlock *hwlock;
int ret; int ret;
...@@ -232,34 +305,47 @@ int hwspinlock_example2(void) ...@@ -232,34 +305,47 @@ int hwspinlock_example2(void)
... ...
return ret; return ret;
} }
API for implementors
====================
4. API for implementors ::
int hwspin_lock_register(struct hwspinlock_device *bank, struct device *dev, int hwspin_lock_register(struct hwspinlock_device *bank, struct device *dev,
const struct hwspinlock_ops *ops, int base_id, int num_locks); 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 To be called from the underlying platform-specific implementation, in
numerous locks). Should be called from a process context (this function order to register a new hwspinlock device (which is usually a bank of
might sleep). numerous locks). Should be called from a process context (this function
Returns 0 on success, or appropriate error code on failure. might sleep).
Returns 0 on success, or appropriate error code on failure.
::
int hwspin_lock_unregister(struct hwspinlock_device *bank); 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 struct hwspinlock_device is a device which usually contains a bank
of hardware locks. It is registered by the underlying hwspinlock of hardware locks. It is registered by the underlying hwspinlock
implementation using the hwspin_lock_register() API. implementation using the hwspin_lock_register() API.
/** ::
/**
* struct hwspinlock_device - a device which usually spans numerous hwspinlocks * struct hwspinlock_device - a device which usually spans numerous hwspinlocks
* @dev: underlying device, will be used to invoke runtime PM api * @dev: underlying device, will be used to invoke runtime PM api
* @ops: platform-specific hwspinlock handlers * @ops: platform-specific hwspinlock handlers
...@@ -267,51 +353,52 @@ implementation using the hwspin_lock_register() API. ...@@ -267,51 +353,52 @@ implementation using the hwspin_lock_register() API.
* @num_locks: number of locks in this device * @num_locks: number of locks in this device
* @lock: dynamically allocated array of 'struct hwspinlock' * @lock: dynamically allocated array of 'struct hwspinlock'
*/ */
struct hwspinlock_device { struct hwspinlock_device {
struct device *dev; struct device *dev;
const struct hwspinlock_ops *ops; const struct hwspinlock_ops *ops;
int base_id; int base_id;
int num_locks; int num_locks;
struct hwspinlock lock[0]; struct hwspinlock lock[0];
}; };
struct hwspinlock_device contains an array of hwspinlock structs, each 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 * struct hwspinlock - this struct represents a single hwspinlock instance
* @bank: the hwspinlock_device structure which owns this lock * @bank: the hwspinlock_device structure which owns this lock
* @lock: initialized and used by hwspinlock core * @lock: initialized and used by hwspinlock core
* @priv: private data, owned by the underlying platform-specific hwspinlock drv * @priv: private data, owned by the underlying platform-specific hwspinlock drv
*/ */
struct hwspinlock { struct hwspinlock {
struct hwspinlock_device *bank; struct hwspinlock_device *bank;
spinlock_t lock; spinlock_t lock;
void *priv; void *priv;
}; };
When registering a bank of locks, the hwspinlock driver only needs to 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 set the priv members of the locks. The rest of the members are set and
initialized by the hwspinlock core itself. 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 { struct hwspinlock_ops {
int (*trylock)(struct hwspinlock *lock); int (*trylock)(struct hwspinlock *lock);
void (*unlock)(struct hwspinlock *lock); void (*unlock)(struct hwspinlock *lock);
void (*relax)(struct hwspinlock *lock); void (*relax)(struct hwspinlock *lock);
}; };
The first two callbacks are mandatory: The first two callbacks are mandatory:
The ->trylock() callback should make a single attempt to take the lock, and 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, 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 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 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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