| /* |
| * 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. |
| */ |
| |
| /* 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(CHOSEN_TICKET, 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; |
| unsigned int 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); |
| |
| /* Wait for the contender to get their ticket */ |
| do { |
| read_cache_op(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 && (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(); |
| } |