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hwspinlock: add the 'in_atomic' API 

Add the 'in_atomic' mode which can be called from an atomic context.
This mode relies on the existing 'raw' mode (no lock, no preemption/irq
disabling) with the difference that the timeout is not based on jiffies
(jiffies won't increase when irq are disabled) but handled with
busy-waiting udelay() calls.

Signed-off-by: Fabien Dessenne <fabien.dessenne@st.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
This commit is contained in:
Fabien Dessenne 2019-03-07 16:58:23 +01:00 committed by Bjorn Andersson
parent bce6f52213
commit 360aa640a5
3 changed files with 127 additions and 16 deletions
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39
Documentation/hwspinlock.txt
View File

@ -151,6 +151,22 @@ notably -ETIMEDOUT if the hwspinlock is still busy after timeout msecs).
The function will never sleep.
::
int hwspin_lock_timeout_in_atomic(struct hwspinlock *hwlock, unsigned int to);
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.
This function shall be called only from an atomic context and the timeout
value shall not exceed a few msecs.
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);
@ -216,6 +232,19 @@ 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_in_atomic(struct hwspinlock *hwlock);
Attempt to lock a previously-assigned hwspinlock, but immediately fail if
it is already taken.
This function shall be called only from an atomic context.
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);
@ -262,6 +291,16 @@ The caller should **never** unlock an hwspinlock which is already unlocked.
Doing so is considered a bug (there is no protection against this).
This function will never sleep.
::
void hwspin_unlock_in_atomic(struct hwspinlock *hwlock);
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).
This function will never sleep.
::
int hwspin_lock_get_id(struct hwspinlock *hwlock);

39
drivers/hwspinlock/hwspinlock_core.c
View File

@ -9,6 +9,7 @@
#define pr_fmt(fmt) "%s: " fmt, __func__
#include <linux/delay.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/spinlock.h>
@ -23,6 +24,9 @@
#include "hwspinlock_internal.h"
/* retry delay used in atomic context */
#define HWSPINLOCK_RETRY_DELAY_US 100
/* radix tree tags */
#define HWSPINLOCK_UNUSED (0) /* tags an hwspinlock as unused */
@ -68,11 +72,11 @@ static DEFINE_MUTEX(hwspinlock_tree_lock);
* user need some time-consuming or sleepable operations under the hardware
* lock, they need one sleepable lock (like mutex) to protect the operations.
*
* If the mode is not HWLOCK_RAW, upon a successful return from this function,
* preemption (and possibly interrupts) is disabled, so the caller must not
* sleep, and is advised to release the hwspinlock as soon as possible. This is
* required in order to minimize remote cores polling on the hardware
* interconnect.
* If the mode is neither HWLOCK_IN_ATOMIC nor HWLOCK_RAW, upon a successful
* return from this function, preemption (and possibly interrupts) is disabled,
* so the caller must not sleep, and is advised to release the hwspinlock as
* soon as possible. This is required in order to minimize remote cores polling
* on the hardware interconnect.
*
* The user decides whether local interrupts are disabled or not, and if yes,
* whether he wants their previous state to be saved. It is up to the user
@ -112,6 +116,7 @@ int __hwspin_trylock(struct hwspinlock *hwlock, int mode, unsigned long *flags)
ret = spin_trylock_irq(&hwlock->lock);
break;
case HWLOCK_RAW:
case HWLOCK_IN_ATOMIC:
ret = 1;
break;
default:
@ -136,6 +141,7 @@ int __hwspin_trylock(struct hwspinlock *hwlock, int mode, unsigned long *flags)
spin_unlock_irq(&hwlock->lock);
break;
case HWLOCK_RAW:
case HWLOCK_IN_ATOMIC:
/* Nothing to do */
break;
default:
@ -179,11 +185,14 @@ EXPORT_SYMBOL_GPL(__hwspin_trylock);
* user need some time-consuming or sleepable operations under the hardware
* lock, they need one sleepable lock (like mutex) to protect the operations.
*
* If the mode is not HWLOCK_RAW, upon a successful return from this function,
* preemption is disabled (and possibly local interrupts, too), so the caller
* must not sleep, and is advised to release the hwspinlock as soon as possible.
* This is required in order to minimize remote cores polling on the
* hardware interconnect.
* If the mode is HWLOCK_IN_ATOMIC (called from an atomic context) the timeout
* is handled with busy-waiting delays, hence shall not exceed few msecs.
*
* If the mode is neither HWLOCK_IN_ATOMIC nor HWLOCK_RAW, upon a successful
* return from this function, preemption (and possibly interrupts) is disabled,
* so the caller must not sleep, and is advised to release the hwspinlock as
* soon as possible. This is required in order to minimize remote cores polling
* on the hardware interconnect.
*
* The user decides whether local interrupts are disabled or not, and if yes,
* whether he wants their previous state to be saved. It is up to the user
@ -198,7 +207,7 @@ int __hwspin_lock_timeout(struct hwspinlock *hwlock, unsigned int to,
int mode, unsigned long *flags)
{
int ret;
unsigned long expire;
unsigned long expire, atomic_delay = 0;
expire = msecs_to_jiffies(to) + jiffies;
@ -212,8 +221,15 @@ int __hwspin_lock_timeout(struct hwspinlock *hwlock, unsigned int to,
* The lock is already taken, let's check if the user wants
* us to try again
*/
if (mode == HWLOCK_IN_ATOMIC) {
udelay(HWSPINLOCK_RETRY_DELAY_US);
atomic_delay += HWSPINLOCK_RETRY_DELAY_US;
if (atomic_delay > to * 1000)
return -ETIMEDOUT;
} else {
if (time_is_before_eq_jiffies(expire))
return -ETIMEDOUT;
}
/*
* Allow platform-specific relax handlers to prevent
@ -276,6 +292,7 @@ void __hwspin_unlock(struct hwspinlock *hwlock, int mode, unsigned long *flags)
spin_unlock_irq(&hwlock->lock);
break;
case HWLOCK_RAW:
case HWLOCK_IN_ATOMIC:
/* Nothing to do */
break;
default:

55
include/linux/hwspinlock.h
View File

@ -17,6 +17,7 @@
#define HWLOCK_IRQSTATE 0x01 /* Disable interrupts, save state */
#define HWLOCK_IRQ 0x02 /* Disable interrupts, don't save state */
#define HWLOCK_RAW 0x03
#define HWLOCK_IN_ATOMIC 0x04 /* Called while in atomic context */
struct device;
struct device_node;
@ -222,6 +223,23 @@ static inline int hwspin_trylock_raw(struct hwspinlock *hwlock)
return __hwspin_trylock(hwlock, HWLOCK_RAW, NULL);
}
/**
* hwspin_trylock_in_atomic() - attempt to lock a specific hwspinlock
* @hwlock: an hwspinlock which we want to trylock
*
* This function attempts to lock an hwspinlock, and will immediately fail
* if the hwspinlock is already taken.
*
* This function shall be called only from an atomic context.
*
* Returns 0 if we successfully locked the hwspinlock, -EBUSY if
* the hwspinlock was already taken, and -EINVAL if @hwlock is invalid.
*/
static inline int hwspin_trylock_in_atomic(struct hwspinlock *hwlock)
{
return __hwspin_trylock(hwlock, HWLOCK_IN_ATOMIC, NULL);
}
/**
* hwspin_trylock() - attempt to lock a specific hwspinlock
* @hwlock: an hwspinlock which we want to trylock
@ -312,6 +330,28 @@ int hwspin_lock_timeout_raw(struct hwspinlock *hwlock, unsigned int to)
return __hwspin_lock_timeout(hwlock, to, HWLOCK_RAW, NULL);
}
/**
* hwspin_lock_timeout_in_atomic() - lock an hwspinlock with timeout limit
* @hwlock: the hwspinlock to be locked
* @to: timeout value in msecs
*
* This function locks the underlying @hwlock. If the @hwlock
* is already taken, the function will busy loop waiting for it to
* be released, but give up when @timeout msecs have elapsed.
*
* This function shall be called only from an atomic context and the timeout
* value shall not exceed a few msecs.
*
* Returns 0 when the @hwlock was successfully taken, and an appropriate
* error code otherwise (most notably an -ETIMEDOUT if the @hwlock is still
* busy after @timeout msecs). The function will never sleep.
*/
static inline
int hwspin_lock_timeout_in_atomic(struct hwspinlock *hwlock, unsigned int to)
{
return __hwspin_lock_timeout(hwlock, to, HWLOCK_IN_ATOMIC, NULL);
}
/**
* hwspin_lock_timeout() - lock an hwspinlock with timeout limit
* @hwlock: the hwspinlock to be locked
@ -386,6 +426,21 @@ static inline void hwspin_unlock_raw(struct hwspinlock *hwlock)
__hwspin_unlock(hwlock, HWLOCK_RAW, NULL);
}
/**
* hwspin_unlock_in_atomic() - unlock hwspinlock
* @hwlock: a previously-acquired hwspinlock which we want to unlock
*
* This function will unlock a specific hwspinlock.
*
* @hwlock must be already locked (e.g. by hwspin_trylock()) before calling
* this function: it is a bug to call unlock on a @hwlock that is already
* unlocked.
*/
static inline void hwspin_unlock_in_atomic(struct hwspinlock *hwlock)
{
__hwspin_unlock(hwlock, HWLOCK_IN_ATOMIC, NULL);
}
/**
* hwspin_unlock() - unlock hwspinlock
* @hwlock: a previously-acquired hwspinlock which we want to unlock