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/***********************license start***************
* Copyright (c) 2003-2010 Cavium Inc. (support@cavium.com). All rights
* reserved.
*
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* * Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following
* disclaimer in the documentation and/or other materials provided
* with the distribution.
* * Neither the name of Cavium Inc. nor the names of
* its contributors may be used to endorse or promote products
* derived from this software without specific prior written
* permission.
* This Software, including technical data, may be subject to U.S. export control
* laws, including the U.S. Export Administration Act and its associated
* regulations, and may be subject to export or import regulations in other
* countries.
* TO THE MAXIMUM EXTENT PERMITTED BY LAW, THE SOFTWARE IS PROVIDED "AS IS"
* AND WITH ALL FAULTS AND CAVIUM INC. MAKES NO PROMISES, REPRESENTATIONS OR
* WARRANTIES, EITHER EXPRESS, IMPLIED, STATUTORY, OR OTHERWISE, WITH RESPECT TO
* THE SOFTWARE, INCLUDING ITS CONDITION, ITS CONFORMITY TO ANY REPRESENTATION OR
* DESCRIPTION, OR THE EXISTENCE OF ANY LATENT OR PATENT DEFECTS, AND CAVIUM
* SPECIFICALLY DISCLAIMS ALL IMPLIED (IF ANY) WARRANTIES OF TITLE,
* MERCHANTABILITY, NONINFRINGEMENT, FITNESS FOR A PARTICULAR PURPOSE, LACK OF
* VIRUSES, ACCURACY OR COMPLETENESS, QUIET ENJOYMENT, QUIET POSSESSION OR
* CORRESPONDENCE TO DESCRIPTION. THE ENTIRE RISK ARISING OUT OF USE OR
* PERFORMANCE OF THE SOFTWARE LIES WITH YOU.
***********************license end**************************************/
/**
* @file
*
* This file provides reader/writer locks.
*
* <hr>$Revision: 70030 $<hr>
*
*
*/
#ifndef __CVMX_RWLOCK_H__
#define __CVMX_RWLOCK_H__
/* include to get atomic compare and store */
#include "cvmx-atomic.h"
#ifdef __cplusplus
extern "C" {
#endif
/* Flags for lock value in rw lock structure */
#define CVMX_RWLOCK_WRITE_FLAG 0x1
#define CVMX_RWLOCK_READ_INC 0x2
/* Writer preference locks (wp). Can be starved by writers. When a writer
* is waiting, no readers are given the lock until all writers are done.
*/
typedef struct
{
volatile uint32_t lock;
volatile uint32_t write_req;
volatile uint32_t write_comp;
} cvmx_rwlock_wp_lock_t;
/**
* Initialize a reader/writer lock. This must be done
* by a single core before used.
*
* @param lock pointer to rwlock structure
*/
static inline void cvmx_rwlock_wp_init(cvmx_rwlock_wp_lock_t *lock)
{
lock->lock = 0;
lock->write_req = 0;
lock->write_comp = 0;
}
/**
* Perform a reader lock. If a writer is pending, this
* will wait for that writer to complete before locking.
*
* NOTE: Each thread/process must only lock any rwlock
* once, or else a deadlock may result.
*
* @param lock pointer to rwlock structure
*/
static inline void cvmx_rwlock_wp_read_lock(cvmx_rwlock_wp_lock_t *lock)
{
/* Wait for outstanding write requests to be serviced */
while (lock->write_req != lock->write_comp)
;
/* Add ourselves to interested reader count */
cvmx_atomic_add32_nosync((int32_t *)&(lock->lock), CVMX_RWLOCK_READ_INC);
/* Wait for writer to finish. No writer will start again
** until after we are done since we have already incremented
** the reader count
*/
while (lock->lock & CVMX_RWLOCK_WRITE_FLAG)
;
}
/**
* Perform a reader unlock.
*
* @param lock pointer to rwlock structure
*/
static inline void cvmx_rwlock_wp_read_unlock(cvmx_rwlock_wp_lock_t *lock)
{
/* Remove ourselves to reader count */
cvmx_atomic_add32_nosync((int32_t *)&(lock->lock), -CVMX_RWLOCK_READ_INC);
}
/**
* Perform a writer lock. Any readers that attempt
* to get a lock while there are any pending write locks
* will wait until all writers have completed. Starvation
* of readers by writers is possible and must be avoided
* by the application.
*
* @param lock pointer to rwlock structure
*/
static inline void cvmx_rwlock_wp_write_lock(cvmx_rwlock_wp_lock_t *lock)
{
/* Get previous value of write requests */
uint32_t prev_writers = ((uint32_t)cvmx_atomic_fetch_and_add32((int32_t *)&(lock->write_req), 1));
/* Spin until our turn */
while (prev_writers != lock->write_comp)
;
/* Spin until no other readers or writers, then set write flag */
while (!cvmx_atomic_compare_and_store32((uint32_t *)&(lock->lock), 0, CVMX_RWLOCK_WRITE_FLAG))
;
}
/**
* Perform a writer unlock.
*
* @param lock pointer to rwlock structure
*/
static inline void cvmx_rwlock_wp_write_unlock(cvmx_rwlock_wp_lock_t *lock)
{
/* Remove our writer flag */
CVMX_SYNCWS; /* Make sure all writes in protected region are visible before unlock */
cvmx_atomic_add32_nosync((int32_t *)&(lock->lock), -CVMX_RWLOCK_WRITE_FLAG);
cvmx_atomic_add32_nosync((int32_t *)&(lock->write_comp), 1);
CVMX_SYNCWS; /* push unlock writes out, but don't stall */
}
#ifdef __cplusplus
}
#endif
#endif /* __CVMX_RWLOCK_H__ */
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