diff options
Diffstat (limited to 'lib/locks/bakery/bakery_lock_normal.c')
-rw-r--r-- | lib/locks/bakery/bakery_lock_normal.c | 217 |
1 files changed, 217 insertions, 0 deletions
diff --git a/lib/locks/bakery/bakery_lock_normal.c b/lib/locks/bakery/bakery_lock_normal.c new file mode 100644 index 0000000000..a325fd4feb --- /dev/null +++ b/lib/locks/bakery/bakery_lock_normal.c @@ -0,0 +1,217 @@ +/* + * 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(); +} |