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 /* Convert a ticket to priority */ 60 #define PRIORITY(t, pos) (((t) << 8) | (pos)) 61 62 #define CHOOSING_TICKET 0x1 63 #define CHOOSING_DONE 0x0 64 65 #define bakery_is_choosing(info) (info & 0x1) 66 #define bakery_ticket_number(info) ((info >> 1) & 0x7FFF) 67 #define make_bakery_data(choosing, number) \ 68 (((choosing & 0x1) | (number << 1)) & 0xFFFF) 69 70 /* This macro assumes that the bakery_info array is located at the offset specified */ 71 #define get_my_bakery_info(offset, id) \ 72 (((bakery_info_t *) (((uint8_t *)_cpu_data()) + offset)) + id) 73 74 #define get_bakery_info_by_index(offset, id, ix) \ 75 (((bakery_info_t *) (((uint8_t *)_cpu_data_by_index(ix)) + offset)) + id) 76 77 #define write_cache_op(addr, cached) \ 78 do { \ 79 (cached ? dccvac((uint64_t)addr) :\ 80 dcivac((uint64_t)addr));\ 81 dsbish();\ 82 } while (0) 83 84 #define read_cache_op(addr, cached) if (cached) \ 85 dccivac((uint64_t)addr) 86 87 static unsigned int bakery_get_ticket(int id, unsigned int offset, 88 unsigned int me, int is_cached) 89 { 90 unsigned int my_ticket, their_ticket; 91 unsigned int they; 92 bakery_info_t *my_bakery_info, *their_bakery_info; 93 94 /* 95 * Obtain a reference to the bakery information for this cpu and ensure 96 * it is not NULL. 97 */ 98 my_bakery_info = get_my_bakery_info(offset, id); 99 assert(my_bakery_info); 100 101 /* 102 * Tell other contenders that we are through the bakery doorway i.e. 103 * going to allocate a ticket for this cpu. 104 */ 105 my_ticket = 0; 106 my_bakery_info->lock_data = make_bakery_data(CHOOSING_TICKET, my_ticket); 107 108 write_cache_op(my_bakery_info, is_cached); 109 110 /* 111 * Iterate through the bakery information of each contender to allocate 112 * the highest ticket number for this cpu. 113 */ 114 for (they = 0; they < BAKERY_LOCK_MAX_CPUS; they++) { 115 if (me == they) 116 continue; 117 118 /* 119 * Get a reference to the other contender's bakery info and 120 * ensure that a stale copy is not read. 121 */ 122 their_bakery_info = get_bakery_info_by_index(offset, id, they); 123 assert(their_bakery_info); 124 125 read_cache_op(their_bakery_info, is_cached); 126 127 /* 128 * Update this cpu's ticket number if a higher ticket number is 129 * seen 130 */ 131 their_ticket = bakery_ticket_number(their_bakery_info->lock_data); 132 if (their_ticket > my_ticket) 133 my_ticket = their_ticket; 134 } 135 136 /* 137 * Compute ticket; then signal to other contenders waiting for us to 138 * finish calculating our ticket value that we're done 139 */ 140 ++my_ticket; 141 my_bakery_info->lock_data = make_bakery_data(CHOOSING_DONE, my_ticket); 142 143 write_cache_op(my_bakery_info, is_cached); 144 145 return my_ticket; 146 } 147 148 void bakery_lock_get(unsigned int id, unsigned int offset) 149 { 150 unsigned int they, me, is_cached; 151 unsigned int my_ticket, my_prio, their_ticket; 152 bakery_info_t *their_bakery_info; 153 uint16_t their_bakery_data; 154 155 me = platform_get_core_pos(read_mpidr_el1()); 156 157 is_cached = read_sctlr_el3() & SCTLR_C_BIT; 158 159 /* Get a ticket */ 160 my_ticket = bakery_get_ticket(id, offset, me, is_cached); 161 162 /* 163 * Now that we got our ticket, compute our priority value, then compare 164 * with that of others, and proceed to acquire the lock 165 */ 166 my_prio = PRIORITY(my_ticket, me); 167 for (they = 0; they < BAKERY_LOCK_MAX_CPUS; they++) { 168 if (me == they) 169 continue; 170 171 /* 172 * Get a reference to the other contender's bakery info and 173 * ensure that a stale copy is not read. 174 */ 175 their_bakery_info = get_bakery_info_by_index(offset, id, they); 176 assert(their_bakery_info); 177 read_cache_op(their_bakery_info, is_cached); 178 179 their_bakery_data = their_bakery_info->lock_data; 180 181 /* Wait for the contender to get their ticket */ 182 while (bakery_is_choosing(their_bakery_data)) { 183 read_cache_op(their_bakery_info, is_cached); 184 their_bakery_data = their_bakery_info->lock_data; 185 } 186 187 /* 188 * If the other party is a contender, they'll have non-zero 189 * (valid) ticket value. If they do, compare priorities 190 */ 191 their_ticket = bakery_ticket_number(their_bakery_data); 192 if (their_ticket && (PRIORITY(their_ticket, they) < my_prio)) { 193 /* 194 * They have higher priority (lower value). Wait for 195 * their ticket value to change (either release the lock 196 * to have it dropped to 0; or drop and probably content 197 * again for the same lock to have an even higher value) 198 */ 199 do { 200 wfe(); 201 read_cache_op(their_bakery_info, is_cached); 202 } while (their_ticket 203 == bakery_ticket_number(their_bakery_info->lock_data)); 204 } 205 } 206 } 207 208 void bakery_lock_release(unsigned int id, unsigned int offset) 209 { 210 bakery_info_t *my_bakery_info; 211 unsigned int is_cached = read_sctlr_el3() & SCTLR_C_BIT; 212 213 my_bakery_info = get_my_bakery_info(offset, id); 214 my_bakery_info->lock_data = 0; 215 write_cache_op(my_bakery_info, is_cached); 216 sev(); 217 } 218