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

 /*
  * Copyright (c) 2015-2018, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */

 #include <assert.h>
 #include <string.h>

 #include <arch_helpers.h>
 #include <lib/bakery_lock.h>
 #include <lib/el3_runtime/cpu_data.h>
 #include <lib/utils_def.h>
 #include <plat/common/platform.h>

 /*
  * Functions in this file implement Bakery Algorithm for mutual exclusion with the
  * bakery lock data structures in cacheable and Normal memory.
  *
  * 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, 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 cacheable and Normal.
  *
  * Note that the ARM architecture guarantees single-copy atomicity for aligned
  * accesses regardless of status of address translation.
  */

 #ifdef PLAT_PERCPU_BAKERY_LOCK_SIZE
 /*
  * Verify that the platform defined value for the per-cpu space for bakery locks is
  * a multiple of the cache line size, to prevent multiple CPUs writing to the same
  * bakery lock cache line
  *
  * Using this value, if provided, rather than the linker generated value results in
  * more efficient code
  */
 CASSERT((PLAT_PERCPU_BAKERY_LOCK_SIZE & (CACHE_WRITEBACK_GRANULE - 1)) == 0, \
 	PLAT_PERCPU_BAKERY_LOCK_SIZE_not_cacheline_multiple);
 #define PERCPU_BAKERY_LOCK_SIZE (PLAT_PERCPU_BAKERY_LOCK_SIZE)
 #else
 /*
  * Use the linker defined symbol which has evaluated the size reqiurement.
  * This is not as efficient as using a platform defined constant
  */
 IMPORT_SYM(uintptr_t, __PERCPU_BAKERY_LOCK_SIZE__, PERCPU_BAKERY_LOCK_SIZE);
 #endif

 static inline bakery_lock_t *get_bakery_info(unsigned int cpu_ix,
 					     bakery_lock_t *lock)
 {
 	return (bakery_info_t *)((uintptr_t)lock +
 				cpu_ix * PERCPU_BAKERY_LOCK_SIZE);
 }

 static inline void write_cache_op(uintptr_t addr, bool cached)
 {
 	if (cached)
 		dccvac(addr);
 	else
 		dcivac(addr);

 	dsbish();
 }

 static inline void read_cache_op(uintptr_t addr, bool cached)
 {
 	if (cached)
 		dccivac(addr);
 }

 /* Helper function to check if the lock is acquired */
 static inline bool is_lock_acquired(const bakery_info_t *my_bakery_info,
 							int is_cached)
 {
 	/*
 	 * Even though lock data is updated only by the owning cpu and
 	 * appropriate cache maintenance operations are performed,
 	 * if the previous update was done when the cpu was not participating
 	 * in coherency, then there is a chance that cache maintenance
 	 * operations were not propagated to all the caches in the system.
 	 * Hence do a `read_cache_op()` prior to read.
 	 */
 	read_cache_op((uintptr_t)my_bakery_info, is_cached);
 	return bakery_ticket_number(my_bakery_info->lock_data) != 0U;
 }

 static unsigned int bakery_get_ticket(bakery_lock_t *lock,
 						unsigned int me, int is_cached)
 {
 	unsigned int my_ticket, their_ticket;
 	unsigned int they;
 	bakery_info_t *my_bakery_info, *their_bakery_info;

 	/*
 	 * Obtain a reference to the bakery information for this cpu and ensure
 	 * it is not NULL.
 	 */
 	my_bakery_info = get_bakery_info(me, lock);
 	assert(my_bakery_info != NULL);

 	/* Prevent recursive acquisition.*/
 	assert(!is_lock_acquired(my_bakery_info, is_cached));

 	/*
 	 * Tell other contenders that we are through the bakery doorway i.e.
 	 * going to allocate a ticket for this cpu.
 	 */
 	my_ticket = 0U;
 	my_bakery_info->lock_data = make_bakery_data(CHOOSING_TICKET, my_ticket);

 	write_cache_op((uintptr_t)my_bakery_info, is_cached);

 	/*
 	 * Iterate through the bakery information of each contender to allocate
 	 * the highest ticket number for this cpu.
 	 */
 	for (they = 0U; they < BAKERY_LOCK_MAX_CPUS; they++) {
 		if (me == they)
 			continue;

 		/*
 		 * Get a reference to the other contender's bakery info and
 		 * ensure that a stale copy is not read.
 		 */
 		their_bakery_info = get_bakery_info(they, lock);
 		assert(their_bakery_info != NULL);

 		read_cache_op((uintptr_t)their_bakery_info, is_cached);

 		/*
 		 * Update this cpu's ticket number if a higher ticket number is
 		 * seen
 		 */
 		their_ticket = bakery_ticket_number(their_bakery_info->lock_data);
 		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;
 	my_bakery_info->lock_data = make_bakery_data(CHOSEN_TICKET, my_ticket);

 	write_cache_op((uintptr_t)my_bakery_info, is_cached);

 	return my_ticket;
 }

 void bakery_lock_get(bakery_lock_t *lock)
 {
 	unsigned int they, me, is_cached;
 	unsigned int my_ticket, my_prio, their_ticket;
 	bakery_info_t *their_bakery_info;
 	unsigned int their_bakery_data;

 	me = plat_my_core_pos();
 #ifdef AARCH32
 	is_cached = read_sctlr() & SCTLR_C_BIT;
 #else
 	is_cached = read_sctlr_el3() & SCTLR_C_BIT;
 #endif

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

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

 		/*
 		 * Get a reference to the other contender's bakery info and
 		 * ensure that a stale copy is not read.
 		 */
 		their_bakery_info = get_bakery_info(they, lock);
 		assert(their_bakery_info != NULL);

 		/* Wait for the contender to get their ticket */
 		do {
 			read_cache_op((uintptr_t)their_bakery_info, is_cached);
 			their_bakery_data = their_bakery_info->lock_data;
 		} while (bakery_is_choosing(their_bakery_data));

 		/*
 		 * If the other party is a contender, they'll have non-zero
 		 * (valid) ticket value. If they do, compare priorities
 		 */
 		their_ticket = bakery_ticket_number(their_bakery_data);
 		if (their_ticket && (bakery_get_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();
 				read_cache_op((uintptr_t)their_bakery_info, is_cached);
 			} while (their_ticket
 				== bakery_ticket_number(their_bakery_info->lock_data));
 		}
 	}

 	/*
 	 * Lock acquired. Ensure that any reads from a shared resource in the
 	 * critical section read values after the lock is acquired.
 	 */
 	dmbld();
 }

 void bakery_lock_release(bakery_lock_t *lock)
 {
 	bakery_info_t *my_bakery_info;
 #ifdef AARCH32
 	unsigned int is_cached = read_sctlr() & SCTLR_C_BIT;
 #else
 	unsigned int is_cached = read_sctlr_el3() & SCTLR_C_BIT;
 #endif

 	my_bakery_info = get_bakery_info(plat_my_core_pos(), lock);

 	assert(is_lock_acquired(my_bakery_info, is_cached));

 	/*
 	 * Ensure that other observers see any stores in the critical section
 	 * before releasing the lock. Release the lock by resetting ticket.
 	 * Then signal other waiting contenders.
 	 */
 	dmbst();
 	my_bakery_info->lock_data = 0U;
 	write_cache_op((uintptr_t)my_bakery_info, is_cached);
 	sev();
 }
	/*
	* Copyright (c) 2015-2018, ARM Limited and Contributors. All rights reserved.
	*
	* SPDX-License-Identifier: BSD-3-Clause
	*/

	#include <assert.h>
	#include <string.h>

	#include <arch_helpers.h>
	#include <lib/bakery_lock.h>
	#include <lib/el3_runtime/cpu_data.h>
	#include <lib/utils_def.h>
	#include <plat/common/platform.h>

	/*
	* Functions in this file implement Bakery Algorithm for mutual exclusion with the
	* bakery lock data structures in cacheable and Normal memory.
	*
	* 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, 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 cacheable and Normal.
	*
	* Note that the ARM architecture guarantees single-copy atomicity for aligned
	* accesses regardless of status of address translation.
	*/

	#ifdef PLAT_PERCPU_BAKERY_LOCK_SIZE
	/*
	* Verify that the platform defined value for the per-cpu space for bakery locks is
	* a multiple of the cache line size, to prevent multiple CPUs writing to the same
	* bakery lock cache line
	*
	* Using this value, if provided, rather than the linker generated value results in
	* more efficient code
	*/
	CASSERT((PLAT_PERCPU_BAKERY_LOCK_SIZE & (CACHE_WRITEBACK_GRANULE - 1)) == 0, \
	PLAT_PERCPU_BAKERY_LOCK_SIZE_not_cacheline_multiple);
	#define PERCPU_BAKERY_LOCK_SIZE (PLAT_PERCPU_BAKERY_LOCK_SIZE)
	#else
	/*
	* Use the linker defined symbol which has evaluated the size reqiurement.
	* This is not as efficient as using a platform defined constant
	*/
	IMPORT_SYM(uintptr_t, __PERCPU_BAKERY_LOCK_SIZE__, PERCPU_BAKERY_LOCK_SIZE);
	#endif

	static inline bakery_lock_t *get_bakery_info(unsigned int cpu_ix,
	bakery_lock_t *lock)
	{
	return (bakery_info_t *)((uintptr_t)lock +
	cpu_ix * PERCPU_BAKERY_LOCK_SIZE);
	}

	static inline void write_cache_op(uintptr_t addr, bool cached)
	{
	if (cached)
	dccvac(addr);
	else
	dcivac(addr);

	dsbish();
	}

	static inline void read_cache_op(uintptr_t addr, bool cached)
	{
	if (cached)
	dccivac(addr);
	}

	/* Helper function to check if the lock is acquired */
	static inline bool is_lock_acquired(const bakery_info_t *my_bakery_info,
	int is_cached)
	{
	/*
	* Even though lock data is updated only by the owning cpu and
	* appropriate cache maintenance operations are performed,
	* if the previous update was done when the cpu was not participating
	* in coherency, then there is a chance that cache maintenance
	* operations were not propagated to all the caches in the system.
	* Hence do a `read_cache_op()` prior to read.
	*/
	read_cache_op((uintptr_t)my_bakery_info, is_cached);
	return bakery_ticket_number(my_bakery_info->lock_data) != 0U;
	}

	static unsigned int bakery_get_ticket(bakery_lock_t *lock,
	unsigned int me, int is_cached)
	{
	unsigned int my_ticket, their_ticket;
	unsigned int they;
	bakery_info_t my_bakery_info, their_bakery_info;

	/*
	* Obtain a reference to the bakery information for this cpu and ensure
	* it is not NULL.
	*/
	my_bakery_info = get_bakery_info(me, lock);
	assert(my_bakery_info != NULL);

	/* Prevent recursive acquisition.*/
	assert(!is_lock_acquired(my_bakery_info, is_cached));

	/*
	* Tell other contenders that we are through the bakery doorway i.e.
	* going to allocate a ticket for this cpu.
	*/
	my_ticket = 0U;
	my_bakery_info->lock_data = make_bakery_data(CHOOSING_TICKET, my_ticket);

	write_cache_op((uintptr_t)my_bakery_info, is_cached);

	/*
	* Iterate through the bakery information of each contender to allocate
	* the highest ticket number for this cpu.
	*/
	for (they = 0U; they < BAKERY_LOCK_MAX_CPUS; they++) {
	if (me == they)
	continue;

	/*
	* Get a reference to the other contender's bakery info and
	* ensure that a stale copy is not read.
	*/
	their_bakery_info = get_bakery_info(they, lock);
	assert(their_bakery_info != NULL);

	read_cache_op((uintptr_t)their_bakery_info, is_cached);

	/*
	* Update this cpu's ticket number if a higher ticket number is
	* seen
	*/
	their_ticket = bakery_ticket_number(their_bakery_info->lock_data);
	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;
	my_bakery_info->lock_data = make_bakery_data(CHOSEN_TICKET, my_ticket);

	write_cache_op((uintptr_t)my_bakery_info, is_cached);

	return my_ticket;
	}

	void bakery_lock_get(bakery_lock_t *lock)
	{
	unsigned int they, me, is_cached;
	unsigned int my_ticket, my_prio, their_ticket;
	bakery_info_t *their_bakery_info;
	unsigned int their_bakery_data;

	me = plat_my_core_pos();
	#ifdef AARCH32
	is_cached = read_sctlr() & SCTLR_C_BIT;
	#else
	is_cached = read_sctlr_el3() & SCTLR_C_BIT;
	#endif

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

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

	/*
	* Get a reference to the other contender's bakery info and
	* ensure that a stale copy is not read.
	*/
	their_bakery_info = get_bakery_info(they, lock);
	assert(their_bakery_info != NULL);

	/* Wait for the contender to get their ticket */
	do {
	read_cache_op((uintptr_t)their_bakery_info, is_cached);
	their_bakery_data = their_bakery_info->lock_data;
	} while (bakery_is_choosing(their_bakery_data));

	/*
	* If the other party is a contender, they'll have non-zero
	* (valid) ticket value. If they do, compare priorities
	*/
	their_ticket = bakery_ticket_number(their_bakery_data);
	if (their_ticket && (bakery_get_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();
	read_cache_op((uintptr_t)their_bakery_info, is_cached);
	} while (their_ticket
	== bakery_ticket_number(their_bakery_info->lock_data));
	}
	}

	/*
	* Lock acquired. Ensure that any reads from a shared resource in the
	* critical section read values after the lock is acquired.
	*/
	dmbld();
	}

	void bakery_lock_release(bakery_lock_t *lock)
	{
	bakery_info_t *my_bakery_info;
	#ifdef AARCH32
	unsigned int is_cached = read_sctlr() & SCTLR_C_BIT;
	#else
	unsigned int is_cached = read_sctlr_el3() & SCTLR_C_BIT;
	#endif

	my_bakery_info = get_bakery_info(plat_my_core_pos(), lock);

	assert(is_lock_acquired(my_bakery_info, is_cached));

	/*
	* Ensure that other observers see any stores in the critical section
	* before releasing the lock. Release the lock by resetting ticket.
	* Then signal other waiting contenders.
	*/
	dmbst();
	my_bakery_info->lock_data = 0U;
	write_cache_op((uintptr_t)my_bakery_info, is_cached);
	sev();
	}