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 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 /* 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 /* 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; 137 my_bakery_info->lock_data = make_bakery_data(CHOSEN_TICKET, my_ticket); 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; 149 unsigned int their_bakery_data; 150 151 me = platform_get_core_pos(read_mpidr_el1()); 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); 173 174 /* Wait for the contender to get their ticket */ 175 do { 176 read_cache_op(their_bakery_info, is_cached); 177 their_bakery_data = their_bakery_info->lock_data; 178 } while (bakery_is_choosing(their_bakery_data)); 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 } 199 /* Lock acquired */ 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); 208 assert(bakery_ticket_number(my_bakery_info->lock_data)); 209 210 my_bakery_info->lock_data = 0; 211 write_cache_op(my_bakery_info, is_cached); 212 sev(); 213 } 214