Achin Gupta | 4f6ad66 | 2013-10-25 09:08:21 +0100 | [diff] [blame] | 1 | /* |
Dan Handley | e83b0ca | 2014-01-14 18:17:09 +0000 | [diff] [blame] | 2 | * Copyright (c) 2013-2014, ARM Limited and Contributors. All rights reserved. |
Achin Gupta | 4f6ad66 | 2013-10-25 09:08:21 +0100 | [diff] [blame] | 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 | |
Jeenu Viswambharan | 82a0aca | 2014-03-13 11:16:25 +0000 | [diff] [blame] | 31 | #include <arch_helpers.h> |
Dan Handley | 97043ac | 2014-04-09 13:14:54 +0100 | [diff] [blame^] | 32 | #include <assert.h> |
| 33 | #include <bakery_lock.h> |
| 34 | #include <string.h> |
Jeenu Viswambharan | 82a0aca | 2014-03-13 11:16:25 +0000 | [diff] [blame] | 35 | |
| 36 | /* |
| 37 | * Functions in this file implement Bakery Algorithm for mutual exclusion. |
| 38 | * |
| 39 | * ARM architecture offers a family of exclusive access instructions to |
| 40 | * efficiently implement mutual exclusion with hardware support. However, as |
| 41 | * well as depending on external hardware, the these instructions have defined |
| 42 | * behavior only on certain memory types (cacheable and Normal memory in |
| 43 | * particular; see ARMv8 Architecture Reference Manual section B2.10). Use cases |
| 44 | * in trusted firmware are such that mutual exclusion implementation cannot |
| 45 | * expect that accesses to the lock have the specific type required by the |
| 46 | * architecture for these primitives to function (for example, not all |
| 47 | * contenders may have address translation enabled). |
| 48 | * |
| 49 | * This implementation does not use mutual exclusion primitives. It expects |
| 50 | * memory regions where the locks reside to be fully ordered and coherent |
| 51 | * (either by disabling address translation, or by assigning proper attributes |
| 52 | * when translation is enabled). |
| 53 | * |
| 54 | * Note that the ARM architecture guarantees single-copy atomicity for aligned |
| 55 | * accesses regardless of status of address translation. |
| 56 | */ |
Achin Gupta | 4f6ad66 | 2013-10-25 09:08:21 +0100 | [diff] [blame] | 57 | |
| 58 | #define assert_bakery_entry_valid(entry, bakery) do { \ |
| 59 | assert(bakery); \ |
| 60 | assert(entry < BAKERY_LOCK_MAX_CPUS); \ |
Dan Handley | 4ecca33 | 2014-04-09 12:48:25 +0100 | [diff] [blame] | 61 | } while (0) |
Achin Gupta | 4f6ad66 | 2013-10-25 09:08:21 +0100 | [diff] [blame] | 62 | |
Jeenu Viswambharan | 82a0aca | 2014-03-13 11:16:25 +0000 | [diff] [blame] | 63 | /* Convert a ticket to priority */ |
| 64 | #define PRIORITY(t, pos) (((t) << 8) | (pos)) |
| 65 | |
| 66 | |
| 67 | /* Initialize Bakery Lock to reset ownership and all ticket values */ |
Dan Handley | fb037bf | 2014-04-10 15:37:22 +0100 | [diff] [blame] | 68 | void bakery_lock_init(bakery_lock_t *bakery) |
Achin Gupta | 4f6ad66 | 2013-10-25 09:08:21 +0100 | [diff] [blame] | 69 | { |
| 70 | assert(bakery); |
Jeenu Viswambharan | 82a0aca | 2014-03-13 11:16:25 +0000 | [diff] [blame] | 71 | |
| 72 | /* All ticket values need to be 0 */ |
Achin Gupta | 4f6ad66 | 2013-10-25 09:08:21 +0100 | [diff] [blame] | 73 | memset(bakery, 0, sizeof(*bakery)); |
| 74 | bakery->owner = NO_OWNER; |
| 75 | } |
| 76 | |
Jeenu Viswambharan | 82a0aca | 2014-03-13 11:16:25 +0000 | [diff] [blame] | 77 | |
| 78 | /* Obtain a ticket for a given CPU */ |
Dan Handley | fb037bf | 2014-04-10 15:37:22 +0100 | [diff] [blame] | 79 | static unsigned int bakery_get_ticket(bakery_lock_t *bakery, unsigned int me) |
Achin Gupta | 4f6ad66 | 2013-10-25 09:08:21 +0100 | [diff] [blame] | 80 | { |
Jeenu Viswambharan | 82a0aca | 2014-03-13 11:16:25 +0000 | [diff] [blame] | 81 | unsigned int my_ticket, their_ticket; |
| 82 | unsigned int they; |
Achin Gupta | 4f6ad66 | 2013-10-25 09:08:21 +0100 | [diff] [blame] | 83 | |
Jeenu Viswambharan | 82a0aca | 2014-03-13 11:16:25 +0000 | [diff] [blame] | 84 | /* |
| 85 | * Flag that we're busy getting our ticket. All CPUs are iterated in the |
| 86 | * order of their ordinal position to decide the maximum ticket value |
| 87 | * observed so far. Our priority is set to be greater than the maximum |
| 88 | * observed priority |
| 89 | * |
| 90 | * Note that it's possible that more than one contender gets the same |
| 91 | * ticket value. That's OK as the lock is acquired based on the priority |
| 92 | * value, not the ticket value alone. |
| 93 | */ |
| 94 | my_ticket = 0; |
| 95 | bakery->entering[me] = 1; |
| 96 | for (they = 0; they < BAKERY_LOCK_MAX_CPUS; they++) { |
| 97 | their_ticket = bakery->number[they]; |
| 98 | if (their_ticket > my_ticket) |
| 99 | my_ticket = their_ticket; |
Achin Gupta | 4f6ad66 | 2013-10-25 09:08:21 +0100 | [diff] [blame] | 100 | } |
| 101 | |
Jeenu Viswambharan | 82a0aca | 2014-03-13 11:16:25 +0000 | [diff] [blame] | 102 | /* |
| 103 | * Compute ticket; then signal to other contenders waiting for us to |
| 104 | * finish calculating our ticket value that we're done |
| 105 | */ |
| 106 | ++my_ticket; |
| 107 | bakery->number[me] = my_ticket; |
| 108 | bakery->entering[me] = 0; |
| 109 | sev(); |
| 110 | |
| 111 | return my_ticket; |
Achin Gupta | 4f6ad66 | 2013-10-25 09:08:21 +0100 | [diff] [blame] | 112 | } |
| 113 | |
Jeenu Viswambharan | 82a0aca | 2014-03-13 11:16:25 +0000 | [diff] [blame] | 114 | |
| 115 | /* |
| 116 | * Acquire bakery lock |
| 117 | * |
| 118 | * Contending CPUs need first obtain a non-zero ticket and then calculate |
| 119 | * priority value. A contending CPU iterate over all other CPUs in the platform, |
| 120 | * which may be contending for the same lock, in the order of their ordinal |
| 121 | * position (CPU0, CPU1 and so on). A non-contending CPU will have its ticket |
| 122 | * (and priority) value as 0. The contending CPU compares its priority with that |
| 123 | * of others'. The CPU with the highest priority (lowest numerical value) |
| 124 | * acquires the lock |
| 125 | */ |
Dan Handley | fb037bf | 2014-04-10 15:37:22 +0100 | [diff] [blame] | 126 | void bakery_lock_get(unsigned long mpidr, bakery_lock_t *bakery) |
Jeenu Viswambharan | 82a0aca | 2014-03-13 11:16:25 +0000 | [diff] [blame] | 127 | { |
| 128 | unsigned int they, me; |
| 129 | unsigned int my_ticket, my_prio, their_ticket; |
| 130 | |
| 131 | me = platform_get_core_pos(mpidr); |
| 132 | |
| 133 | assert_bakery_entry_valid(me, bakery); |
| 134 | |
| 135 | /* Prevent recursive acquisition */ |
| 136 | assert(bakery->owner != me); |
| 137 | |
| 138 | /* Get a ticket */ |
| 139 | my_ticket = bakery_get_ticket(bakery, me); |
| 140 | |
| 141 | /* |
| 142 | * Now that we got our ticket, compute our priority value, then compare |
| 143 | * with that of others, and proceed to acquire the lock |
| 144 | */ |
| 145 | my_prio = PRIORITY(my_ticket, me); |
| 146 | for (they = 0; they < BAKERY_LOCK_MAX_CPUS; they++) { |
| 147 | if (me == they) |
| 148 | continue; |
| 149 | |
| 150 | /* Wait for the contender to get their ticket */ |
| 151 | while (bakery->entering[they]) |
| 152 | wfe(); |
| 153 | |
| 154 | /* |
| 155 | * If the other party is a contender, they'll have non-zero |
| 156 | * (valid) ticket value. If they do, compare priorities |
| 157 | */ |
| 158 | their_ticket = bakery->number[they]; |
| 159 | if (their_ticket && (PRIORITY(their_ticket, they) < my_prio)) { |
| 160 | /* |
| 161 | * They have higher priority (lower value). Wait for |
| 162 | * their ticket value to change (either release the lock |
| 163 | * to have it dropped to 0; or drop and probably content |
| 164 | * again for the same lock to have an even higher value) |
| 165 | */ |
| 166 | do { |
| 167 | wfe(); |
| 168 | } while (their_ticket == bakery->number[they]); |
| 169 | } |
| 170 | } |
| 171 | |
| 172 | /* Lock acquired */ |
| 173 | bakery->owner = me; |
| 174 | } |
| 175 | |
| 176 | |
| 177 | /* Release the lock and signal contenders */ |
Dan Handley | fb037bf | 2014-04-10 15:37:22 +0100 | [diff] [blame] | 178 | void bakery_lock_release(unsigned long mpidr, bakery_lock_t *bakery) |
Achin Gupta | 4f6ad66 | 2013-10-25 09:08:21 +0100 | [diff] [blame] | 179 | { |
Jeenu Viswambharan | 82a0aca | 2014-03-13 11:16:25 +0000 | [diff] [blame] | 180 | unsigned int me = platform_get_core_pos(mpidr); |
Achin Gupta | 4f6ad66 | 2013-10-25 09:08:21 +0100 | [diff] [blame] | 181 | |
Jeenu Viswambharan | 82a0aca | 2014-03-13 11:16:25 +0000 | [diff] [blame] | 182 | assert_bakery_entry_valid(me, bakery); |
| 183 | assert(bakery->owner == me); |
Achin Gupta | 4f6ad66 | 2013-10-25 09:08:21 +0100 | [diff] [blame] | 184 | |
Jeenu Viswambharan | 82a0aca | 2014-03-13 11:16:25 +0000 | [diff] [blame] | 185 | /* |
| 186 | * Release lock by resetting ownership and ticket. Then signal other |
| 187 | * waiting contenders |
| 188 | */ |
Achin Gupta | 4f6ad66 | 2013-10-25 09:08:21 +0100 | [diff] [blame] | 189 | bakery->owner = NO_OWNER; |
Jeenu Viswambharan | 82a0aca | 2014-03-13 11:16:25 +0000 | [diff] [blame] | 190 | bakery->number[me] = 0; |
| 191 | sev(); |
Achin Gupta | 4f6ad66 | 2013-10-25 09:08:21 +0100 | [diff] [blame] | 192 | } |