Soby Mathew | 8c5fe0b | 2015-01-08 18:02:19 +0000 | [diff] [blame] | 1 | /* |
| 2 | * Copyright (c) 2015, ARM Limited and Contributors. All rights reserved. |
| 3 | * |
| 4 | * Redistribution and use in source and binary forms, with or without |
| 5 | * modification, are permitted provided that the following conditions are met: |
| 6 | * |
| 7 | * Redistributions of source code must retain the above copyright notice, this |
| 8 | * list of conditions and the following disclaimer. |
| 9 | * |
| 10 | * Redistributions in binary form must reproduce the above copyright notice, |
| 11 | * this list of conditions and the following disclaimer in the documentation |
| 12 | * and/or other materials provided with the distribution. |
| 13 | * |
| 14 | * Neither the name of ARM nor the names of its contributors may be used |
| 15 | * to endorse or promote products derived from this software without specific |
| 16 | * prior written permission. |
| 17 | * |
| 18 | * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" |
| 19 | * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE |
| 20 | * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE |
| 21 | * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE |
| 22 | * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR |
| 23 | * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF |
| 24 | * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS |
| 25 | * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN |
| 26 | * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) |
| 27 | * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE |
| 28 | * POSSIBILITY OF SUCH DAMAGE. |
| 29 | */ |
| 30 | |
| 31 | #include <arch_helpers.h> |
| 32 | #include <assert.h> |
| 33 | #include <bakery_lock.h> |
| 34 | #include <cpu_data.h> |
| 35 | #include <platform.h> |
| 36 | #include <string.h> |
| 37 | |
| 38 | /* |
| 39 | * Functions in this file implement Bakery Algorithm for mutual exclusion with the |
| 40 | * bakery lock data structures in cacheable and Normal memory. |
| 41 | * |
| 42 | * ARM architecture offers a family of exclusive access instructions to |
| 43 | * efficiently implement mutual exclusion with hardware support. However, as |
| 44 | * well as depending on external hardware, these instructions have defined |
| 45 | * behavior only on certain memory types (cacheable and Normal memory in |
| 46 | * particular; see ARMv8 Architecture Reference Manual section B2.10). Use cases |
| 47 | * in trusted firmware are such that mutual exclusion implementation cannot |
| 48 | * expect that accesses to the lock have the specific type required by the |
| 49 | * architecture for these primitives to function (for example, not all |
| 50 | * contenders may have address translation enabled). |
| 51 | * |
| 52 | * This implementation does not use mutual exclusion primitives. It expects |
| 53 | * memory regions where the locks reside to be cacheable and Normal. |
| 54 | * |
| 55 | * Note that the ARM architecture guarantees single-copy atomicity for aligned |
| 56 | * accesses regardless of status of address translation. |
| 57 | */ |
| 58 | |
Soby Mathew | 8c5fe0b | 2015-01-08 18:02:19 +0000 | [diff] [blame] | 59 | /* This macro assumes that the bakery_info array is located at the offset specified */ |
| 60 | #define get_my_bakery_info(offset, id) \ |
| 61 | (((bakery_info_t *) (((uint8_t *)_cpu_data()) + offset)) + id) |
| 62 | |
| 63 | #define get_bakery_info_by_index(offset, id, ix) \ |
| 64 | (((bakery_info_t *) (((uint8_t *)_cpu_data_by_index(ix)) + offset)) + id) |
| 65 | |
| 66 | #define write_cache_op(addr, cached) \ |
| 67 | do { \ |
| 68 | (cached ? dccvac((uint64_t)addr) :\ |
| 69 | dcivac((uint64_t)addr));\ |
| 70 | dsbish();\ |
| 71 | } while (0) |
| 72 | |
| 73 | #define read_cache_op(addr, cached) if (cached) \ |
| 74 | dccivac((uint64_t)addr) |
| 75 | |
| 76 | static unsigned int bakery_get_ticket(int id, unsigned int offset, |
| 77 | unsigned int me, int is_cached) |
| 78 | { |
| 79 | unsigned int my_ticket, their_ticket; |
| 80 | unsigned int they; |
| 81 | bakery_info_t *my_bakery_info, *their_bakery_info; |
| 82 | |
| 83 | /* |
| 84 | * Obtain a reference to the bakery information for this cpu and ensure |
| 85 | * it is not NULL. |
| 86 | */ |
| 87 | my_bakery_info = get_my_bakery_info(offset, id); |
| 88 | assert(my_bakery_info); |
| 89 | |
| 90 | /* |
Soby Mathew | 548579f | 2015-02-20 16:04:17 +0000 | [diff] [blame] | 91 | * Prevent recursive acquisition. |
| 92 | * Since lock data is written to and cleaned by the owning cpu, it |
| 93 | * doesn't require any cache operations prior to reading the lock data. |
| 94 | */ |
| 95 | assert(!bakery_ticket_number(my_bakery_info->lock_data)); |
| 96 | |
| 97 | /* |
Soby Mathew | 8c5fe0b | 2015-01-08 18:02:19 +0000 | [diff] [blame] | 98 | * Tell other contenders that we are through the bakery doorway i.e. |
| 99 | * going to allocate a ticket for this cpu. |
| 100 | */ |
| 101 | my_ticket = 0; |
| 102 | my_bakery_info->lock_data = make_bakery_data(CHOOSING_TICKET, my_ticket); |
| 103 | |
| 104 | write_cache_op(my_bakery_info, is_cached); |
| 105 | |
| 106 | /* |
| 107 | * Iterate through the bakery information of each contender to allocate |
| 108 | * the highest ticket number for this cpu. |
| 109 | */ |
| 110 | for (they = 0; they < BAKERY_LOCK_MAX_CPUS; they++) { |
| 111 | if (me == they) |
| 112 | continue; |
| 113 | |
| 114 | /* |
| 115 | * Get a reference to the other contender's bakery info and |
| 116 | * ensure that a stale copy is not read. |
| 117 | */ |
| 118 | their_bakery_info = get_bakery_info_by_index(offset, id, they); |
| 119 | assert(their_bakery_info); |
| 120 | |
| 121 | read_cache_op(their_bakery_info, is_cached); |
| 122 | |
| 123 | /* |
| 124 | * Update this cpu's ticket number if a higher ticket number is |
| 125 | * seen |
| 126 | */ |
| 127 | their_ticket = bakery_ticket_number(their_bakery_info->lock_data); |
| 128 | if (their_ticket > my_ticket) |
| 129 | my_ticket = their_ticket; |
| 130 | } |
| 131 | |
| 132 | /* |
| 133 | * Compute ticket; then signal to other contenders waiting for us to |
| 134 | * finish calculating our ticket value that we're done |
| 135 | */ |
| 136 | ++my_ticket; |
Soby Mathew | 1c9573a | 2015-02-19 16:23:51 +0000 | [diff] [blame] | 137 | my_bakery_info->lock_data = make_bakery_data(CHOSEN_TICKET, my_ticket); |
Soby Mathew | 8c5fe0b | 2015-01-08 18:02:19 +0000 | [diff] [blame] | 138 | |
| 139 | write_cache_op(my_bakery_info, is_cached); |
| 140 | |
| 141 | return my_ticket; |
| 142 | } |
| 143 | |
| 144 | void bakery_lock_get(unsigned int id, unsigned int offset) |
| 145 | { |
| 146 | unsigned int they, me, is_cached; |
| 147 | unsigned int my_ticket, my_prio, their_ticket; |
| 148 | bakery_info_t *their_bakery_info; |
Soby Mathew | 1c9573a | 2015-02-19 16:23:51 +0000 | [diff] [blame] | 149 | unsigned int their_bakery_data; |
Soby Mathew | 8c5fe0b | 2015-01-08 18:02:19 +0000 | [diff] [blame] | 150 | |
Soby Mathew | 85a181c | 2015-07-13 11:21:11 +0100 | [diff] [blame^] | 151 | me = plat_my_core_pos(); |
Soby Mathew | 8c5fe0b | 2015-01-08 18:02:19 +0000 | [diff] [blame] | 152 | |
| 153 | is_cached = read_sctlr_el3() & SCTLR_C_BIT; |
| 154 | |
| 155 | /* Get a ticket */ |
| 156 | my_ticket = bakery_get_ticket(id, offset, me, is_cached); |
| 157 | |
| 158 | /* |
| 159 | * Now that we got our ticket, compute our priority value, then compare |
| 160 | * with that of others, and proceed to acquire the lock |
| 161 | */ |
| 162 | my_prio = PRIORITY(my_ticket, me); |
| 163 | for (they = 0; they < BAKERY_LOCK_MAX_CPUS; they++) { |
| 164 | if (me == they) |
| 165 | continue; |
| 166 | |
| 167 | /* |
| 168 | * Get a reference to the other contender's bakery info and |
| 169 | * ensure that a stale copy is not read. |
| 170 | */ |
| 171 | their_bakery_info = get_bakery_info_by_index(offset, id, they); |
| 172 | assert(their_bakery_info); |
Soby Mathew | 8c5fe0b | 2015-01-08 18:02:19 +0000 | [diff] [blame] | 173 | |
| 174 | /* Wait for the contender to get their ticket */ |
Soby Mathew | 1c9573a | 2015-02-19 16:23:51 +0000 | [diff] [blame] | 175 | do { |
Soby Mathew | 8c5fe0b | 2015-01-08 18:02:19 +0000 | [diff] [blame] | 176 | read_cache_op(their_bakery_info, is_cached); |
| 177 | their_bakery_data = their_bakery_info->lock_data; |
Soby Mathew | 1c9573a | 2015-02-19 16:23:51 +0000 | [diff] [blame] | 178 | } while (bakery_is_choosing(their_bakery_data)); |
Soby Mathew | 8c5fe0b | 2015-01-08 18:02:19 +0000 | [diff] [blame] | 179 | |
| 180 | /* |
| 181 | * If the other party is a contender, they'll have non-zero |
| 182 | * (valid) ticket value. If they do, compare priorities |
| 183 | */ |
| 184 | their_ticket = bakery_ticket_number(their_bakery_data); |
| 185 | if (their_ticket && (PRIORITY(their_ticket, they) < my_prio)) { |
| 186 | /* |
| 187 | * They have higher priority (lower value). Wait for |
| 188 | * their ticket value to change (either release the lock |
| 189 | * to have it dropped to 0; or drop and probably content |
| 190 | * again for the same lock to have an even higher value) |
| 191 | */ |
| 192 | do { |
| 193 | wfe(); |
| 194 | read_cache_op(their_bakery_info, is_cached); |
| 195 | } while (their_ticket |
| 196 | == bakery_ticket_number(their_bakery_info->lock_data)); |
| 197 | } |
| 198 | } |
Soby Mathew | 548579f | 2015-02-20 16:04:17 +0000 | [diff] [blame] | 199 | /* Lock acquired */ |
Soby Mathew | 8c5fe0b | 2015-01-08 18:02:19 +0000 | [diff] [blame] | 200 | } |
| 201 | |
| 202 | void bakery_lock_release(unsigned int id, unsigned int offset) |
| 203 | { |
| 204 | bakery_info_t *my_bakery_info; |
| 205 | unsigned int is_cached = read_sctlr_el3() & SCTLR_C_BIT; |
| 206 | |
| 207 | my_bakery_info = get_my_bakery_info(offset, id); |
Soby Mathew | 548579f | 2015-02-20 16:04:17 +0000 | [diff] [blame] | 208 | assert(bakery_ticket_number(my_bakery_info->lock_data)); |
| 209 | |
Soby Mathew | 8c5fe0b | 2015-01-08 18:02:19 +0000 | [diff] [blame] | 210 | my_bakery_info->lock_data = 0; |
| 211 | write_cache_op(my_bakery_info, is_cached); |
| 212 | sev(); |
| 213 | } |