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Soby Mathew523d6332015-01-08 18:02:19 +00001/*
Joel Hutton5cc3bc82018-03-21 11:40:57 +00002 * Copyright (c) 2015-2018, ARM Limited and Contributors. All rights reserved.
Soby Mathew523d6332015-01-08 18:02:19 +00003 *
dp-armfa3cf0b2017-05-03 09:38:09 +01004 * SPDX-License-Identifier: BSD-3-Clause
Soby Mathew523d6332015-01-08 18:02:19 +00005 */
6
Soby Mathew523d6332015-01-08 18:02:19 +00007#include <assert.h>
Soby Mathew523d6332015-01-08 18:02:19 +00008#include <string.h>
Antonio Nino Diaze0f90632018-12-14 00:18:21 +00009
10#include <arch_helpers.h>
11#include <lib/bakery_lock.h>
12#include <lib/el3_runtime/cpu_data.h>
13#include <lib/utils_def.h>
14#include <plat/common/platform.h>
Soby Mathew523d6332015-01-08 18:02:19 +000015
16/*
17 * Functions in this file implement Bakery Algorithm for mutual exclusion with the
18 * bakery lock data structures in cacheable and Normal memory.
19 *
20 * ARM architecture offers a family of exclusive access instructions to
21 * efficiently implement mutual exclusion with hardware support. However, as
22 * well as depending on external hardware, these instructions have defined
23 * behavior only on certain memory types (cacheable and Normal memory in
24 * particular; see ARMv8 Architecture Reference Manual section B2.10). Use cases
25 * in trusted firmware are such that mutual exclusion implementation cannot
26 * expect that accesses to the lock have the specific type required by the
27 * architecture for these primitives to function (for example, not all
28 * contenders may have address translation enabled).
29 *
30 * This implementation does not use mutual exclusion primitives. It expects
31 * memory regions where the locks reside to be cacheable and Normal.
32 *
33 * Note that the ARM architecture guarantees single-copy atomicity for aligned
34 * accesses regardless of status of address translation.
35 */
36
Andrew Thoelkee466c9f2015-09-10 11:39:36 +010037#ifdef PLAT_PERCPU_BAKERY_LOCK_SIZE
38/*
39 * Verify that the platform defined value for the per-cpu space for bakery locks is
40 * a multiple of the cache line size, to prevent multiple CPUs writing to the same
41 * bakery lock cache line
42 *
43 * Using this value, if provided, rather than the linker generated value results in
44 * more efficient code
45 */
46CASSERT((PLAT_PERCPU_BAKERY_LOCK_SIZE & (CACHE_WRITEBACK_GRANULE - 1)) == 0, \
47 PLAT_PERCPU_BAKERY_LOCK_SIZE_not_cacheline_multiple);
48#define PERCPU_BAKERY_LOCK_SIZE (PLAT_PERCPU_BAKERY_LOCK_SIZE)
49#else
50/*
51 * Use the linker defined symbol which has evaluated the size reqiurement.
52 * This is not as efficient as using a platform defined constant
53 */
Varun Wadekar77c382c2019-01-30 08:26:20 -080054IMPORT_SYM(uintptr_t, __PERCPU_BAKERY_LOCK_START__, BAKERY_LOCK_START);
55IMPORT_SYM(uintptr_t, __PERCPU_BAKERY_LOCK_END__, BAKERY_LOCK_END);
56#define PERCPU_BAKERY_LOCK_SIZE (BAKERY_LOCK_END - BAKERY_LOCK_START)
Andrew Thoelkee466c9f2015-09-10 11:39:36 +010057#endif
Soby Mathew523d6332015-01-08 18:02:19 +000058
Antonio Nino Diaz519248b2018-10-31 15:55:57 +000059static inline bakery_lock_t *get_bakery_info(unsigned int cpu_ix,
60 bakery_lock_t *lock)
61{
62 return (bakery_info_t *)((uintptr_t)lock +
63 cpu_ix * PERCPU_BAKERY_LOCK_SIZE);
64}
Soby Mathew523d6332015-01-08 18:02:19 +000065
Antonio Nino Diaz519248b2018-10-31 15:55:57 +000066static inline void write_cache_op(uintptr_t addr, bool cached)
67{
68 if (cached)
69 dccvac(addr);
70 else
71 dcivac(addr);
Soby Mathew523d6332015-01-08 18:02:19 +000072
Antonio Nino Diaz519248b2018-10-31 15:55:57 +000073 dsbish();
74}
75
76static inline void read_cache_op(uintptr_t addr, bool cached)
77{
78 if (cached)
79 dccivac(addr);
80}
Soby Mathew523d6332015-01-08 18:02:19 +000081
Soby Mathewf9baaa52016-11-14 17:19:35 +000082/* Helper function to check if the lock is acquired */
Antonio Nino Diaz519248b2018-10-31 15:55:57 +000083static inline bool is_lock_acquired(const bakery_info_t *my_bakery_info,
Soby Mathewf9baaa52016-11-14 17:19:35 +000084 int is_cached)
85{
86 /*
87 * Even though lock data is updated only by the owning cpu and
88 * appropriate cache maintenance operations are performed,
89 * if the previous update was done when the cpu was not participating
90 * in coherency, then there is a chance that cache maintenance
91 * operations were not propagated to all the caches in the system.
92 * Hence do a `read_cache_op()` prior to read.
93 */
Antonio Nino Diaz519248b2018-10-31 15:55:57 +000094 read_cache_op((uintptr_t)my_bakery_info, is_cached);
95 return bakery_ticket_number(my_bakery_info->lock_data) != 0U;
Soby Mathewf9baaa52016-11-14 17:19:35 +000096}
97
Andrew Thoelkee466c9f2015-09-10 11:39:36 +010098static unsigned int bakery_get_ticket(bakery_lock_t *lock,
Soby Mathew523d6332015-01-08 18:02:19 +000099 unsigned int me, int is_cached)
100{
101 unsigned int my_ticket, their_ticket;
102 unsigned int they;
103 bakery_info_t *my_bakery_info, *their_bakery_info;
104
105 /*
106 * Obtain a reference to the bakery information for this cpu and ensure
107 * it is not NULL.
108 */
Andrew Thoelkee466c9f2015-09-10 11:39:36 +0100109 my_bakery_info = get_bakery_info(me, lock);
Antonio Nino Diaz519248b2018-10-31 15:55:57 +0000110 assert(my_bakery_info != NULL);
Soby Mathew523d6332015-01-08 18:02:19 +0000111
Soby Mathewf9baaa52016-11-14 17:19:35 +0000112 /* Prevent recursive acquisition.*/
113 assert(!is_lock_acquired(my_bakery_info, is_cached));
Soby Mathew156280c2015-02-20 16:04:17 +0000114
115 /*
Soby Mathew523d6332015-01-08 18:02:19 +0000116 * Tell other contenders that we are through the bakery doorway i.e.
117 * going to allocate a ticket for this cpu.
118 */
Antonio Nino Diaz519248b2018-10-31 15:55:57 +0000119 my_ticket = 0U;
Soby Mathew523d6332015-01-08 18:02:19 +0000120 my_bakery_info->lock_data = make_bakery_data(CHOOSING_TICKET, my_ticket);
121
Antonio Nino Diaz519248b2018-10-31 15:55:57 +0000122 write_cache_op((uintptr_t)my_bakery_info, is_cached);
Soby Mathew523d6332015-01-08 18:02:19 +0000123
124 /*
125 * Iterate through the bakery information of each contender to allocate
126 * the highest ticket number for this cpu.
127 */
Antonio Nino Diaz519248b2018-10-31 15:55:57 +0000128 for (they = 0U; they < BAKERY_LOCK_MAX_CPUS; they++) {
Soby Mathew523d6332015-01-08 18:02:19 +0000129 if (me == they)
130 continue;
131
132 /*
133 * Get a reference to the other contender's bakery info and
134 * ensure that a stale copy is not read.
135 */
Andrew Thoelkee466c9f2015-09-10 11:39:36 +0100136 their_bakery_info = get_bakery_info(they, lock);
Antonio Nino Diaz519248b2018-10-31 15:55:57 +0000137 assert(their_bakery_info != NULL);
Soby Mathew523d6332015-01-08 18:02:19 +0000138
Antonio Nino Diaz519248b2018-10-31 15:55:57 +0000139 read_cache_op((uintptr_t)their_bakery_info, is_cached);
Soby Mathew523d6332015-01-08 18:02:19 +0000140
141 /*
142 * Update this cpu's ticket number if a higher ticket number is
143 * seen
144 */
145 their_ticket = bakery_ticket_number(their_bakery_info->lock_data);
146 if (their_ticket > my_ticket)
147 my_ticket = their_ticket;
148 }
149
150 /*
151 * Compute ticket; then signal to other contenders waiting for us to
152 * finish calculating our ticket value that we're done
153 */
154 ++my_ticket;
Soby Mathewa0a897d2015-02-19 16:23:51 +0000155 my_bakery_info->lock_data = make_bakery_data(CHOSEN_TICKET, my_ticket);
Soby Mathew523d6332015-01-08 18:02:19 +0000156
Antonio Nino Diaz519248b2018-10-31 15:55:57 +0000157 write_cache_op((uintptr_t)my_bakery_info, is_cached);
Soby Mathew523d6332015-01-08 18:02:19 +0000158
159 return my_ticket;
160}
161
Andrew Thoelkee466c9f2015-09-10 11:39:36 +0100162void bakery_lock_get(bakery_lock_t *lock)
Soby Mathew523d6332015-01-08 18:02:19 +0000163{
164 unsigned int they, me, is_cached;
165 unsigned int my_ticket, my_prio, their_ticket;
166 bakery_info_t *their_bakery_info;
Soby Mathewa0a897d2015-02-19 16:23:51 +0000167 unsigned int their_bakery_data;
Soby Mathew523d6332015-01-08 18:02:19 +0000168
Soby Mathew3700a922015-07-13 11:21:11 +0100169 me = plat_my_core_pos();
Soby Mathew077ab542017-02-14 10:16:18 +0000170#ifdef AARCH32
171 is_cached = read_sctlr() & SCTLR_C_BIT;
172#else
Soby Mathew523d6332015-01-08 18:02:19 +0000173 is_cached = read_sctlr_el3() & SCTLR_C_BIT;
Soby Mathew077ab542017-02-14 10:16:18 +0000174#endif
Soby Mathew523d6332015-01-08 18:02:19 +0000175
176 /* Get a ticket */
Andrew Thoelkee466c9f2015-09-10 11:39:36 +0100177 my_ticket = bakery_get_ticket(lock, me, is_cached);
Soby Mathew523d6332015-01-08 18:02:19 +0000178
179 /*
180 * Now that we got our ticket, compute our priority value, then compare
181 * with that of others, and proceed to acquire the lock
182 */
Antonio Nino Diaz519248b2018-10-31 15:55:57 +0000183 my_prio = bakery_get_priority(my_ticket, me);
184 for (they = 0U; they < BAKERY_LOCK_MAX_CPUS; they++) {
Soby Mathew523d6332015-01-08 18:02:19 +0000185 if (me == they)
186 continue;
187
188 /*
189 * Get a reference to the other contender's bakery info and
190 * ensure that a stale copy is not read.
191 */
Andrew Thoelkee466c9f2015-09-10 11:39:36 +0100192 their_bakery_info = get_bakery_info(they, lock);
Antonio Nino Diaz519248b2018-10-31 15:55:57 +0000193 assert(their_bakery_info != NULL);
Soby Mathew523d6332015-01-08 18:02:19 +0000194
195 /* Wait for the contender to get their ticket */
Soby Mathewa0a897d2015-02-19 16:23:51 +0000196 do {
Antonio Nino Diaz519248b2018-10-31 15:55:57 +0000197 read_cache_op((uintptr_t)their_bakery_info, is_cached);
Soby Mathew523d6332015-01-08 18:02:19 +0000198 their_bakery_data = their_bakery_info->lock_data;
Soby Mathewa0a897d2015-02-19 16:23:51 +0000199 } while (bakery_is_choosing(their_bakery_data));
Soby Mathew523d6332015-01-08 18:02:19 +0000200
201 /*
202 * If the other party is a contender, they'll have non-zero
203 * (valid) ticket value. If they do, compare priorities
204 */
205 their_ticket = bakery_ticket_number(their_bakery_data);
Antonio Nino Diaz519248b2018-10-31 15:55:57 +0000206 if (their_ticket && (bakery_get_priority(their_ticket, they) < my_prio)) {
Soby Mathew523d6332015-01-08 18:02:19 +0000207 /*
208 * They have higher priority (lower value). Wait for
209 * their ticket value to change (either release the lock
210 * to have it dropped to 0; or drop and probably content
211 * again for the same lock to have an even higher value)
212 */
213 do {
214 wfe();
Antonio Nino Diaz519248b2018-10-31 15:55:57 +0000215 read_cache_op((uintptr_t)their_bakery_info, is_cached);
Soby Mathew523d6332015-01-08 18:02:19 +0000216 } while (their_ticket
217 == bakery_ticket_number(their_bakery_info->lock_data));
218 }
219 }
Jeenu Viswambharan0ffd9e22018-08-08 14:10:55 +0100220
221 /*
222 * Lock acquired. Ensure that any reads from a shared resource in the
223 * critical section read values after the lock is acquired.
224 */
225 dmbld();
Soby Mathew523d6332015-01-08 18:02:19 +0000226}
227
Andrew Thoelkee466c9f2015-09-10 11:39:36 +0100228void bakery_lock_release(bakery_lock_t *lock)
Soby Mathew523d6332015-01-08 18:02:19 +0000229{
230 bakery_info_t *my_bakery_info;
Soby Mathew077ab542017-02-14 10:16:18 +0000231#ifdef AARCH32
232 unsigned int is_cached = read_sctlr() & SCTLR_C_BIT;
233#else
Soby Mathew523d6332015-01-08 18:02:19 +0000234 unsigned int is_cached = read_sctlr_el3() & SCTLR_C_BIT;
Soby Mathew077ab542017-02-14 10:16:18 +0000235#endif
Soby Mathew523d6332015-01-08 18:02:19 +0000236
Andrew Thoelkee466c9f2015-09-10 11:39:36 +0100237 my_bakery_info = get_bakery_info(plat_my_core_pos(), lock);
Soby Mathewf9baaa52016-11-14 17:19:35 +0000238
239 assert(is_lock_acquired(my_bakery_info, is_cached));
Soby Mathew156280c2015-02-20 16:04:17 +0000240
Jeenu Viswambharan0ffd9e22018-08-08 14:10:55 +0100241 /*
242 * Ensure that other observers see any stores in the critical section
243 * before releasing the lock. Release the lock by resetting ticket.
244 * Then signal other waiting contenders.
245 */
246 dmbst();
Antonio Nino Diaz519248b2018-10-31 15:55:57 +0000247 my_bakery_info->lock_data = 0U;
248 write_cache_op((uintptr_t)my_bakery_info, is_cached);
Soby Mathew523d6332015-01-08 18:02:19 +0000249 sev();
250}