lib/locks/bakery/bakery_lock.c - filogic/atf - Gitiles

 /*
  * Copyright (c) 2013-2014, ARM Limited and Contributors. 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 ARM 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 IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
  * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
  * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  * POSSIBILITY OF SUCH DAMAGE.
  */

 #include <arch_helpers.h>
 #include <assert.h>
 #include <bakery_lock.h>
 #include <platform.h>
 #include <string.h>

 /*
  * Functions in this file implement Bakery Algorithm for mutual exclusion.
  *
  * ARM architecture offers a family of exclusive access instructions to
  * efficiently implement mutual exclusion with hardware support. However, as
  * well as depending on external hardware, the these instructions have defined
  * behavior only on certain memory types (cacheable and Normal memory in
  * particular; see ARMv8 Architecture Reference Manual section B2.10). Use cases
  * in trusted firmware are such that mutual exclusion implementation cannot
  * expect that accesses to the lock have the specific type required by the
  * architecture for these primitives to function (for example, not all
  * contenders may have address translation enabled).
  *
  * This implementation does not use mutual exclusion primitives. It expects
  * memory regions where the locks reside to be fully ordered and coherent
  * (either by disabling address translation, or by assigning proper attributes
  * when translation is enabled).
  *
  * Note that the ARM architecture guarantees single-copy atomicity for aligned
  * accesses regardless of status of address translation.
  */

 #define assert_bakery_entry_valid(entry, bakery) do {	\
 	assert(bakery);					\
 	assert(entry < BAKERY_LOCK_MAX_CPUS);		\
 } while (0)

 /* Convert a ticket to priority */
 #define PRIORITY(t, pos)	(((t) << 8) | (pos))


 /* Initialize Bakery Lock to reset ownership and all ticket values */
 void bakery_lock_init(bakery_lock_t *bakery)
 {
 	assert(bakery);

 	/* All ticket values need to be 0 */
 	memset(bakery, 0, sizeof(*bakery));
 	bakery->owner = NO_OWNER;
 }


 /* Obtain a ticket for a given CPU */
 static unsigned int bakery_get_ticket(bakery_lock_t *bakery, unsigned int me)
 {
 	unsigned int my_ticket, their_ticket;
 	unsigned int they;

 	/*
 	 * Flag that we're busy getting our ticket. All CPUs are iterated in the
 	 * order of their ordinal position to decide the maximum ticket value
 	 * observed so far. Our priority is set to be greater than the maximum
 	 * observed priority
 	 *
 	 * Note that it's possible that more than one contender gets the same
 	 * ticket value. That's OK as the lock is acquired based on the priority
 	 * value, not the ticket value alone.
 	 */
 	my_ticket = 0;
 	bakery->entering[me] = 1;
 	for (they = 0; they < BAKERY_LOCK_MAX_CPUS; they++) {
 		their_ticket = bakery->number[they];
 		if (their_ticket > my_ticket)
 			my_ticket = their_ticket;
 	}

 	/*
 	 * Compute ticket; then signal to other contenders waiting for us to
 	 * finish calculating our ticket value that we're done
 	 */
 	++my_ticket;
 	bakery->number[me] = my_ticket;
 	bakery->entering[me] = 0;

 	return my_ticket;
 }


 /*
  * Acquire bakery lock
  *
  * Contending CPUs need first obtain a non-zero ticket and then calculate
  * priority value. A contending CPU iterate over all other CPUs in the platform,
  * which may be contending for the same lock, in the order of their ordinal
  * position (CPU0, CPU1 and so on). A non-contending CPU will have its ticket
  * (and priority) value as 0. The contending CPU compares its priority with that
  * of others'. The CPU with the highest priority (lowest numerical value)
  * acquires the lock
  */
 void bakery_lock_get(bakery_lock_t *bakery)
 {
 	unsigned int they, me;
 	unsigned int my_ticket, my_prio, their_ticket;

 	me = platform_get_core_pos(read_mpidr_el1());

 	assert_bakery_entry_valid(me, bakery);

 	/* Prevent recursive acquisition */
 	assert(bakery->owner != me);

 	/* Get a ticket */
 	my_ticket = bakery_get_ticket(bakery, me);

 	/*
 	 * Now that we got our ticket, compute our priority value, then compare
 	 * with that of others, and proceed to acquire the lock
 	 */
 	my_prio = PRIORITY(my_ticket, me);
 	for (they = 0; they < BAKERY_LOCK_MAX_CPUS; they++) {
 		if (me == they)
 			continue;

 		/* Wait for the contender to get their ticket */
 		while (bakery->entering[they])
 			;

 		/*
 		 * If the other party is a contender, they'll have non-zero
 		 * (valid) ticket value. If they do, compare priorities
 		 */
 		their_ticket = bakery->number[they];
 		if (their_ticket && (PRIORITY(their_ticket, they) < my_prio)) {
 			/*
 			 * They have higher priority (lower value). Wait for
 			 * their ticket value to change (either release the lock
 			 * to have it dropped to 0; or drop and probably content
 			 * again for the same lock to have an even higher value)
 			 */
 			do {
 				wfe();
 			} while (their_ticket == bakery->number[they]);
 		}
 	}

 	/* Lock acquired */
 	bakery->owner = me;
 }


 /* Release the lock and signal contenders */
 void bakery_lock_release(bakery_lock_t *bakery)
 {
 	unsigned int me = platform_get_core_pos(read_mpidr_el1());

 	assert_bakery_entry_valid(me, bakery);
 	assert(bakery->owner == me);

 	/*
 	 * Release lock by resetting ownership and ticket. Then signal other
 	 * waiting contenders
 	 */
 	bakery->owner = NO_OWNER;
 	bakery->number[me] = 0;
 	dsb();
 	sev();
 }
	/*
	* Copyright (c) 2013-2014, ARM Limited and Contributors. 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 ARM 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 IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
	* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
	* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
	* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
	* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
	* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
	* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
	* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
	* POSSIBILITY OF SUCH DAMAGE.
	*/

	#include <arch_helpers.h>
	#include <assert.h>
	#include <bakery_lock.h>
	#include <platform.h>
	#include <string.h>

	/*
	* Functions in this file implement Bakery Algorithm for mutual exclusion.
	*
	* ARM architecture offers a family of exclusive access instructions to
	* efficiently implement mutual exclusion with hardware support. However, as
	* well as depending on external hardware, the these instructions have defined
	* behavior only on certain memory types (cacheable and Normal memory in
	* particular; see ARMv8 Architecture Reference Manual section B2.10). Use cases
	* in trusted firmware are such that mutual exclusion implementation cannot
	* expect that accesses to the lock have the specific type required by the
	* architecture for these primitives to function (for example, not all
	* contenders may have address translation enabled).
	*
	* This implementation does not use mutual exclusion primitives. It expects
	* memory regions where the locks reside to be fully ordered and coherent
	* (either by disabling address translation, or by assigning proper attributes
	* when translation is enabled).
	*
	* Note that the ARM architecture guarantees single-copy atomicity for aligned
	* accesses regardless of status of address translation.
	*/

	#define assert_bakery_entry_valid(entry, bakery) do { \
	assert(bakery); \
	assert(entry < BAKERY_LOCK_MAX_CPUS); \
	} while (0)

	/* Convert a ticket to priority */
	#define PRIORITY(t, pos) (((t) << 8) \| (pos))


	/* Initialize Bakery Lock to reset ownership and all ticket values */
	void bakery_lock_init(bakery_lock_t *bakery)
	{
	assert(bakery);

	/* All ticket values need to be 0 */
	memset(bakery, 0, sizeof(*bakery));
	bakery->owner = NO_OWNER;
	}


	/* Obtain a ticket for a given CPU */
	static unsigned int bakery_get_ticket(bakery_lock_t *bakery, unsigned int me)
	{
	unsigned int my_ticket, their_ticket;
	unsigned int they;

	/*
	* Flag that we're busy getting our ticket. All CPUs are iterated in the
	* order of their ordinal position to decide the maximum ticket value
	* observed so far. Our priority is set to be greater than the maximum
	* observed priority
	*
	* Note that it's possible that more than one contender gets the same
	* ticket value. That's OK as the lock is acquired based on the priority
	* value, not the ticket value alone.
	*/
	my_ticket = 0;
	bakery->entering[me] = 1;
	for (they = 0; they < BAKERY_LOCK_MAX_CPUS; they++) {
	their_ticket = bakery->number[they];
	if (their_ticket > my_ticket)
	my_ticket = their_ticket;
	}

	/*
	* Compute ticket; then signal to other contenders waiting for us to
	* finish calculating our ticket value that we're done
	*/
	++my_ticket;
	bakery->number[me] = my_ticket;
	bakery->entering[me] = 0;

	return my_ticket;
	}


	/*
	* Acquire bakery lock
	*
	* Contending CPUs need first obtain a non-zero ticket and then calculate
	* priority value. A contending CPU iterate over all other CPUs in the platform,
	* which may be contending for the same lock, in the order of their ordinal
	* position (CPU0, CPU1 and so on). A non-contending CPU will have its ticket
	* (and priority) value as 0. The contending CPU compares its priority with that
	* of others'. The CPU with the highest priority (lowest numerical value)
	* acquires the lock
	*/
	void bakery_lock_get(bakery_lock_t *bakery)
	{
	unsigned int they, me;
	unsigned int my_ticket, my_prio, their_ticket;

	me = platform_get_core_pos(read_mpidr_el1());

	assert_bakery_entry_valid(me, bakery);

	/* Prevent recursive acquisition */
	assert(bakery->owner != me);

	/* Get a ticket */
	my_ticket = bakery_get_ticket(bakery, me);

	/*
	* Now that we got our ticket, compute our priority value, then compare
	* with that of others, and proceed to acquire the lock
	*/
	my_prio = PRIORITY(my_ticket, me);
	for (they = 0; they < BAKERY_LOCK_MAX_CPUS; they++) {
	if (me == they)
	continue;

	/* Wait for the contender to get their ticket */
	while (bakery->entering[they])
	;

	/*
	* If the other party is a contender, they'll have non-zero
	* (valid) ticket value. If they do, compare priorities
	*/
	their_ticket = bakery->number[they];
	if (their_ticket && (PRIORITY(their_ticket, they) < my_prio)) {
	/*
	* They have higher priority (lower value). Wait for
	* their ticket value to change (either release the lock
	* to have it dropped to 0; or drop and probably content
	* again for the same lock to have an even higher value)
	*/
	do {
	wfe();
	} while (their_ticket == bakery->number[they]);
	}
	}

	/* Lock acquired */
	bakery->owner = me;
	}


	/* Release the lock and signal contenders */
	void bakery_lock_release(bakery_lock_t *bakery)
	{
	unsigned int me = platform_get_core_pos(read_mpidr_el1());

	assert_bakery_entry_valid(me, bakery);
	assert(bakery->owner == me);

	/*
	* Release lock by resetting ownership and ticket. Then signal other
	* waiting contenders
	*/
	bakery->owner = NO_OWNER;
	bakery->number[me] = 0;
	dsb();
	sev();
	}