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+/*
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+ * Copyright (c) 2015, ARM Limited and Contributors. All rights reserved.
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+ *
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+ * Redistribution and use in source and binary forms, with or without
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+ * modification, are permitted provided that the following conditions are met:
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+ *
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+ * Redistributions of source code must retain the above copyright notice, this
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+ * list of conditions and the following disclaimer.
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+ *
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+ * Redistributions in binary form must reproduce the above copyright notice,
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+ * this list of conditions and the following disclaimer in the documentation
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+ * and/or other materials provided with the distribution.
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+ *
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+ * Neither the name of ARM nor the names of its contributors may be used
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+ * to endorse or promote products derived from this software without specific
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+ * prior written permission.
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+ *
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+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
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+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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+ * POSSIBILITY OF SUCH DAMAGE.
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+ */
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+
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+#include <arch_helpers.h>
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+#include <assert.h>
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+#include <bakery_lock.h>
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+#include <cpu_data.h>
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+#include <platform.h>
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+#include <string.h>
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+
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+/*
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+ * Functions in this file implement Bakery Algorithm for mutual exclusion with the
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+ * bakery lock data structures in cacheable and Normal memory.
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+ *
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+ * ARM architecture offers a family of exclusive access instructions to
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+ * efficiently implement mutual exclusion with hardware support. However, as
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+ * well as depending on external hardware, these instructions have defined
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+ * behavior only on certain memory types (cacheable and Normal memory in
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+ * particular; see ARMv8 Architecture Reference Manual section B2.10). Use cases
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+ * in trusted firmware are such that mutual exclusion implementation cannot
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+ * expect that accesses to the lock have the specific type required by the
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+ * architecture for these primitives to function (for example, not all
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+ * contenders may have address translation enabled).
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+ *
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+ * This implementation does not use mutual exclusion primitives. It expects
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+ * memory regions where the locks reside to be cacheable and Normal.
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+ *
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+ * Note that the ARM architecture guarantees single-copy atomicity for aligned
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+ * accesses regardless of status of address translation.
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+ */
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+
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+/* Convert a ticket to priority */
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+#define PRIORITY(t, pos) (((t) << 8) | (pos))
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+
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+#define CHOOSING_TICKET 0x1
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+#define CHOOSING_DONE 0x0
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+
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+#define bakery_is_choosing(info) (info & 0x1)
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+#define bakery_ticket_number(info) ((info >> 1) & 0x7FFF)
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+#define make_bakery_data(choosing, number) \
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+ (((choosing & 0x1) | (number << 1)) & 0xFFFF)
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+
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+/* This macro assumes that the bakery_info array is located at the offset specified */
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+#define get_my_bakery_info(offset, id) \
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+ (((bakery_info_t *) (((uint8_t *)_cpu_data()) + offset)) + id)
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+
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+#define get_bakery_info_by_index(offset, id, ix) \
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+ (((bakery_info_t *) (((uint8_t *)_cpu_data_by_index(ix)) + offset)) + id)
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+
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+#define write_cache_op(addr, cached) \
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+ do { \
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+ (cached ? dccvac((uint64_t)addr) :\
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+ dcivac((uint64_t)addr));\
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+ dsbish();\
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+ } while (0)
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+
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+#define read_cache_op(addr, cached) if (cached) \
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+ dccivac((uint64_t)addr)
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+
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+static unsigned int bakery_get_ticket(int id, unsigned int offset,
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+ unsigned int me, int is_cached)
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+{
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+ unsigned int my_ticket, their_ticket;
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+ unsigned int they;
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+ bakery_info_t *my_bakery_info, *their_bakery_info;
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+
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+ /*
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+ * Obtain a reference to the bakery information for this cpu and ensure
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+ * it is not NULL.
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+ */
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+ my_bakery_info = get_my_bakery_info(offset, id);
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+ assert(my_bakery_info);
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+
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+ /*
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+ * Tell other contenders that we are through the bakery doorway i.e.
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+ * going to allocate a ticket for this cpu.
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+ */
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+ my_ticket = 0;
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+ my_bakery_info->lock_data = make_bakery_data(CHOOSING_TICKET, my_ticket);
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+
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+ write_cache_op(my_bakery_info, is_cached);
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+
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+ /*
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+ * Iterate through the bakery information of each contender to allocate
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+ * the highest ticket number for this cpu.
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+ */
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+ for (they = 0; they < BAKERY_LOCK_MAX_CPUS; they++) {
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+ if (me == they)
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+ continue;
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+
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+ /*
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+ * Get a reference to the other contender's bakery info and
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+ * ensure that a stale copy is not read.
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+ */
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+ their_bakery_info = get_bakery_info_by_index(offset, id, they);
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+ assert(their_bakery_info);
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+
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+ read_cache_op(their_bakery_info, is_cached);
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+
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+ /*
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+ * Update this cpu's ticket number if a higher ticket number is
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+ * seen
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+ */
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+ their_ticket = bakery_ticket_number(their_bakery_info->lock_data);
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+ if (their_ticket > my_ticket)
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+ my_ticket = their_ticket;
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+ }
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+
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+ /*
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+ * Compute ticket; then signal to other contenders waiting for us to
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+ * finish calculating our ticket value that we're done
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+ */
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+ ++my_ticket;
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+ my_bakery_info->lock_data = make_bakery_data(CHOOSING_DONE, my_ticket);
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+
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+ write_cache_op(my_bakery_info, is_cached);
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+
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+ return my_ticket;
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+}
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+
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+void bakery_lock_get(unsigned int id, unsigned int offset)
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+{
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+ unsigned int they, me, is_cached;
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+ unsigned int my_ticket, my_prio, their_ticket;
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+ bakery_info_t *their_bakery_info;
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+ uint16_t their_bakery_data;
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+
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+ me = platform_get_core_pos(read_mpidr_el1());
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+
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+ is_cached = read_sctlr_el3() & SCTLR_C_BIT;
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+
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+ /* Get a ticket */
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+ my_ticket = bakery_get_ticket(id, offset, me, is_cached);
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+
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+ /*
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+ * Now that we got our ticket, compute our priority value, then compare
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+ * with that of others, and proceed to acquire the lock
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+ */
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+ my_prio = PRIORITY(my_ticket, me);
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+ for (they = 0; they < BAKERY_LOCK_MAX_CPUS; they++) {
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+ if (me == they)
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+ continue;
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+
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+ /*
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+ * Get a reference to the other contender's bakery info and
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+ * ensure that a stale copy is not read.
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+ */
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+ their_bakery_info = get_bakery_info_by_index(offset, id, they);
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+ assert(their_bakery_info);
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+ read_cache_op(their_bakery_info, is_cached);
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+
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+ their_bakery_data = their_bakery_info->lock_data;
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+
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+ /* Wait for the contender to get their ticket */
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+ while (bakery_is_choosing(their_bakery_data)) {
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+ read_cache_op(their_bakery_info, is_cached);
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+ their_bakery_data = their_bakery_info->lock_data;
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+ }
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+
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+ /*
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+ * If the other party is a contender, they'll have non-zero
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+ * (valid) ticket value. If they do, compare priorities
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+ */
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+ their_ticket = bakery_ticket_number(their_bakery_data);
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+ if (their_ticket && (PRIORITY(their_ticket, they) < my_prio)) {
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+ /*
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+ * They have higher priority (lower value). Wait for
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+ * their ticket value to change (either release the lock
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+ * to have it dropped to 0; or drop and probably content
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+ * again for the same lock to have an even higher value)
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+ */
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+ do {
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+ wfe();
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+ read_cache_op(their_bakery_info, is_cached);
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+ } while (their_ticket
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+ == bakery_ticket_number(their_bakery_info->lock_data));
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+ }
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+ }
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+}
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+
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+void bakery_lock_release(unsigned int id, unsigned int offset)
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+{
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+ bakery_info_t *my_bakery_info;
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+ unsigned int is_cached = read_sctlr_el3() & SCTLR_C_BIT;
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+
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+ my_bakery_info = get_my_bakery_info(offset, id);
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+ my_bakery_info->lock_data = 0;
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+ write_cache_op(my_bakery_info, is_cached);
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+ sev();
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+}
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