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- /*
- * Copyright (c) 2015, 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 <cpu_data.h>
- #include <platform.h>
- #include <string.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.
- */
- /* Convert a ticket to priority */
- #define PRIORITY(t, pos) (((t) << 8) | (pos))
- #define CHOOSING_TICKET 0x1
- #define CHOOSING_DONE 0x0
- #define bakery_is_choosing(info) (info & 0x1)
- #define bakery_ticket_number(info) ((info >> 1) & 0x7FFF)
- #define make_bakery_data(choosing, number) \
- (((choosing & 0x1) | (number << 1)) & 0xFFFF)
- /* This macro assumes that the bakery_info array is located at the offset specified */
- #define get_my_bakery_info(offset, id) \
- (((bakery_info_t *) (((uint8_t *)_cpu_data()) + offset)) + id)
- #define get_bakery_info_by_index(offset, id, ix) \
- (((bakery_info_t *) (((uint8_t *)_cpu_data_by_index(ix)) + offset)) + id)
- #define write_cache_op(addr, cached) \
- do { \
- (cached ? dccvac((uint64_t)addr) :\
- dcivac((uint64_t)addr));\
- dsbish();\
- } while (0)
- #define read_cache_op(addr, cached) if (cached) \
- dccivac((uint64_t)addr)
- static unsigned int bakery_get_ticket(int id, unsigned int offset,
- 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_my_bakery_info(offset, id);
- assert(my_bakery_info);
- /*
- * Tell other contenders that we are through the bakery doorway i.e.
- * going to allocate a ticket for this cpu.
- */
- my_ticket = 0;
- my_bakery_info->lock_data = make_bakery_data(CHOOSING_TICKET, my_ticket);
- write_cache_op(my_bakery_info, is_cached);
- /*
- * Iterate through the bakery information of each contender to allocate
- * the highest ticket number for this cpu.
- */
- for (they = 0; 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_by_index(offset, id, they);
- assert(their_bakery_info);
- read_cache_op(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(CHOOSING_DONE, my_ticket);
- write_cache_op(my_bakery_info, is_cached);
- return my_ticket;
- }
- void bakery_lock_get(unsigned int id, unsigned int offset)
- {
- unsigned int they, me, is_cached;
- unsigned int my_ticket, my_prio, their_ticket;
- bakery_info_t *their_bakery_info;
- uint16_t their_bakery_data;
- me = platform_get_core_pos(read_mpidr_el1());
- is_cached = read_sctlr_el3() & SCTLR_C_BIT;
- /* Get a ticket */
- my_ticket = bakery_get_ticket(id, offset, 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 = PRIORITY(my_ticket, me);
- for (they = 0; 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_by_index(offset, id, they);
- assert(their_bakery_info);
- read_cache_op(their_bakery_info, is_cached);
- their_bakery_data = their_bakery_info->lock_data;
- /* Wait for the contender to get their ticket */
- while (bakery_is_choosing(their_bakery_data)) {
- read_cache_op(their_bakery_info, is_cached);
- their_bakery_data = their_bakery_info->lock_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 && (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(their_bakery_info, is_cached);
- } while (their_ticket
- == bakery_ticket_number(their_bakery_info->lock_data));
- }
- }
- }
- void bakery_lock_release(unsigned int id, unsigned int offset)
- {
- bakery_info_t *my_bakery_info;
- unsigned int is_cached = read_sctlr_el3() & SCTLR_C_BIT;
- my_bakery_info = get_my_bakery_info(offset, id);
- my_bakery_info->lock_data = 0;
- write_cache_op(my_bakery_info, is_cached);
- sev();
- }
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