1 /* 2 * Copyright (c) 2015-2016, 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 #ifdef PLAT_PERCPU_BAKERY_LOCK_SIZE 60 /* 61 * Verify that the platform defined value for the per-cpu space for bakery locks is 62 * a multiple of the cache line size, to prevent multiple CPUs writing to the same 63 * bakery lock cache line 64 * 65 * Using this value, if provided, rather than the linker generated value results in 66 * more efficient code 67 */ 68 CASSERT((PLAT_PERCPU_BAKERY_LOCK_SIZE & (CACHE_WRITEBACK_GRANULE - 1)) == 0, \ 69 PLAT_PERCPU_BAKERY_LOCK_SIZE_not_cacheline_multiple); 70 #define PERCPU_BAKERY_LOCK_SIZE (PLAT_PERCPU_BAKERY_LOCK_SIZE) 71 #else 72 /* 73 * Use the linker defined symbol which has evaluated the size reqiurement. 74 * This is not as efficient as using a platform defined constant 75 */ 76 extern void *__PERCPU_BAKERY_LOCK_SIZE__; 77 #define PERCPU_BAKERY_LOCK_SIZE ((uintptr_t)&__PERCPU_BAKERY_LOCK_SIZE__) 78 #endif 79 80 #define get_bakery_info(cpu_ix, lock) \ 81 (bakery_info_t *)((uintptr_t)lock + cpu_ix * PERCPU_BAKERY_LOCK_SIZE) 82 83 #define write_cache_op(addr, cached) \ 84 do { \ 85 (cached ? dccvac((uintptr_t)addr) :\ 86 dcivac((uintptr_t)addr));\ 87 dsbish();\ 88 } while (0) 89 90 #define read_cache_op(addr, cached) if (cached) \ 91 dccivac((uintptr_t)addr) 92 93 /* Helper function to check if the lock is acquired */ 94 static inline int is_lock_acquired(const bakery_info_t *my_bakery_info, 95 int is_cached) 96 { 97 /* 98 * Even though lock data is updated only by the owning cpu and 99 * appropriate cache maintenance operations are performed, 100 * if the previous update was done when the cpu was not participating 101 * in coherency, then there is a chance that cache maintenance 102 * operations were not propagated to all the caches in the system. 103 * Hence do a `read_cache_op()` prior to read. 104 */ 105 read_cache_op(my_bakery_info, is_cached); 106 return !!(bakery_ticket_number(my_bakery_info->lock_data)); 107 } 108 109 static unsigned int bakery_get_ticket(bakery_lock_t *lock, 110 unsigned int me, int is_cached) 111 { 112 unsigned int my_ticket, their_ticket; 113 unsigned int they; 114 bakery_info_t *my_bakery_info, *their_bakery_info; 115 116 /* 117 * Obtain a reference to the bakery information for this cpu and ensure 118 * it is not NULL. 119 */ 120 my_bakery_info = get_bakery_info(me, lock); 121 assert(my_bakery_info); 122 123 /* Prevent recursive acquisition.*/ 124 assert(!is_lock_acquired(my_bakery_info, is_cached)); 125 126 /* 127 * Tell other contenders that we are through the bakery doorway i.e. 128 * going to allocate a ticket for this cpu. 129 */ 130 my_ticket = 0; 131 my_bakery_info->lock_data = make_bakery_data(CHOOSING_TICKET, my_ticket); 132 133 write_cache_op(my_bakery_info, is_cached); 134 135 /* 136 * Iterate through the bakery information of each contender to allocate 137 * the highest ticket number for this cpu. 138 */ 139 for (they = 0; they < BAKERY_LOCK_MAX_CPUS; they++) { 140 if (me == they) 141 continue; 142 143 /* 144 * Get a reference to the other contender's bakery info and 145 * ensure that a stale copy is not read. 146 */ 147 their_bakery_info = get_bakery_info(they, lock); 148 assert(their_bakery_info); 149 150 read_cache_op(their_bakery_info, is_cached); 151 152 /* 153 * Update this cpu's ticket number if a higher ticket number is 154 * seen 155 */ 156 their_ticket = bakery_ticket_number(their_bakery_info->lock_data); 157 if (their_ticket > my_ticket) 158 my_ticket = their_ticket; 159 } 160 161 /* 162 * Compute ticket; then signal to other contenders waiting for us to 163 * finish calculating our ticket value that we're done 164 */ 165 ++my_ticket; 166 my_bakery_info->lock_data = make_bakery_data(CHOSEN_TICKET, my_ticket); 167 168 write_cache_op(my_bakery_info, is_cached); 169 170 return my_ticket; 171 } 172 173 void bakery_lock_get(bakery_lock_t *lock) 174 { 175 unsigned int they, me, is_cached; 176 unsigned int my_ticket, my_prio, their_ticket; 177 bakery_info_t *their_bakery_info; 178 unsigned int their_bakery_data; 179 180 me = plat_my_core_pos(); 181 182 is_cached = read_sctlr_el3() & SCTLR_C_BIT; 183 184 /* Get a ticket */ 185 my_ticket = bakery_get_ticket(lock, me, is_cached); 186 187 /* 188 * Now that we got our ticket, compute our priority value, then compare 189 * with that of others, and proceed to acquire the lock 190 */ 191 my_prio = PRIORITY(my_ticket, me); 192 for (they = 0; they < BAKERY_LOCK_MAX_CPUS; they++) { 193 if (me == they) 194 continue; 195 196 /* 197 * Get a reference to the other contender's bakery info and 198 * ensure that a stale copy is not read. 199 */ 200 their_bakery_info = get_bakery_info(they, lock); 201 assert(their_bakery_info); 202 203 /* Wait for the contender to get their ticket */ 204 do { 205 read_cache_op(their_bakery_info, is_cached); 206 their_bakery_data = their_bakery_info->lock_data; 207 } while (bakery_is_choosing(their_bakery_data)); 208 209 /* 210 * If the other party is a contender, they'll have non-zero 211 * (valid) ticket value. If they do, compare priorities 212 */ 213 their_ticket = bakery_ticket_number(their_bakery_data); 214 if (their_ticket && (PRIORITY(their_ticket, they) < my_prio)) { 215 /* 216 * They have higher priority (lower value). Wait for 217 * their ticket value to change (either release the lock 218 * to have it dropped to 0; or drop and probably content 219 * again for the same lock to have an even higher value) 220 */ 221 do { 222 wfe(); 223 read_cache_op(their_bakery_info, is_cached); 224 } while (their_ticket 225 == bakery_ticket_number(their_bakery_info->lock_data)); 226 } 227 } 228 /* Lock acquired */ 229 } 230 231 void bakery_lock_release(bakery_lock_t *lock) 232 { 233 bakery_info_t *my_bakery_info; 234 unsigned int is_cached = read_sctlr_el3() & SCTLR_C_BIT; 235 236 my_bakery_info = get_bakery_info(plat_my_core_pos(), lock); 237 238 assert(is_lock_acquired(my_bakery_info, is_cached)); 239 240 my_bakery_info->lock_data = 0; 241 write_cache_op(my_bakery_info, is_cached); 242 sev(); 243 } 244