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authorLinus Torvalds <torvalds@linux-foundation.org>2017-07-15 22:58:58 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2017-07-15 22:58:58 +0300
commit486088bc4689f826b80aa317b45ac9e42e8b25ee (patch)
treeadf5847a6119d24da990d9e336f005c4a316e6be /Documentation/hwspinlock.txt
parent52f6c588c77b76d548201470c2a28263a41b462b (diff)
parent43e5f7e1fa66531777c49791014c3124ea9208d8 (diff)
downloadlinux-486088bc4689f826b80aa317b45ac9e42e8b25ee.tar.xz
Merge tag 'standardize-docs' of git://git.lwn.net/linux
Pull documentation format standardization from Jonathan Corbet: "This series converts a number of top-level documents to the RST format without incorporating them into the Sphinx tree. The hope is to bring some uniformity to kernel documentation and, perhaps more importantly, have our existing docs serve as an example of the desired formatting for those that will be added later. Mauro has gone through and fixed up a lot of top-level documentation files to make them conform to the RST format, but without moving or renaming them in any way. This will help when we incorporate the ones we want to keep into the Sphinx doctree, but the real purpose is to bring a bit of uniformity to our documentation and let the top-level docs serve as examples for those writing new ones" * tag 'standardize-docs' of git://git.lwn.net/linux: (84 commits) docs: kprobes.txt: Fix whitespacing tee.txt: standardize document format cgroup-v2.txt: standardize document format dell_rbu.txt: standardize document format zorro.txt: standardize document format xz.txt: standardize document format xillybus.txt: standardize document format vfio.txt: standardize document format vfio-mediated-device.txt: standardize document format unaligned-memory-access.txt: standardize document format this_cpu_ops.txt: standardize document format svga.txt: standardize document format static-keys.txt: standardize document format smsc_ece1099.txt: standardize document format SM501.txt: standardize document format siphash.txt: standardize document format sgi-ioc4.txt: standardize document format SAK.txt: standardize document format rpmsg.txt: standardize document format robust-futexes.txt: standardize document format ...
Diffstat (limited to 'Documentation/hwspinlock.txt')
-rw-r--r--Documentation/hwspinlock.txt527
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.