1 files changed, 250 insertions, 0 deletions
diff --git a/lib/locks/bakery/bakery_lock_normal.c b/lib/locks/bakery/bakery_lock_normal.c
new file mode 100644
index 0000000..9f27322
--- /dev/null
+++ b/lib/locks/bakery/bakery_lock_normal.c
@@ -0,0 +1,250 @@
+/*
+ * Copyright (c) 2015-2020, Arm Limited and Contributors. All rights reserved.
+ * Copyright (c) 2020, NVIDIA Corporation. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <assert.h>
+#include <string.h>
+
+#include <arch_helpers.h>
+#include <lib/bakery_lock.h>
+#include <lib/el3_runtime/cpu_data.h>
+#include <lib/utils_def.h>
+#include <plat/common/platform.h>
+
+/*
+ * Functions in this file implement Bakery Algorithm for mutual exclusion with the
+ * bakery lock data structures in cacheable and Normal memory.
+ *
+ * ARM architecture offers a family of exclusive access instructions to
+ * efficiently implement mutual exclusion with hardware support. However, as
+ * well as depending on external hardware, these instructions have defined
+ * behavior only on certain memory types (cacheable and Normal memory in
+ * particular; see ARMv8 Architecture Reference Manual section B2.10). Use cases
+ * in trusted firmware are such that mutual exclusion implementation cannot
+ * expect that accesses to the lock have the specific type required by the
+ * architecture for these primitives to function (for example, not all
+ * contenders may have address translation enabled).
+ *
+ * This implementation does not use mutual exclusion primitives. It expects
+ * memory regions where the locks reside to be cacheable and Normal.
+ *
+ * Note that the ARM architecture guarantees single-copy atomicity for aligned
+ * accesses regardless of status of address translation.
+ */
+
+#ifdef PLAT_PERCPU_BAKERY_LOCK_SIZE
+/*
+ * Verify that the platform defined value for the per-cpu space for bakery locks is
+ * a multiple of the cache line size, to prevent multiple CPUs writing to the same
+ * bakery lock cache line
+ *
+ * Using this value, if provided, rather than the linker generated value results in
+ * more efficient code
+ */
+CASSERT((PLAT_PERCPU_BAKERY_LOCK_SIZE & (CACHE_WRITEBACK_GRANULE - 1)) == 0,
+	PLAT_PERCPU_BAKERY_LOCK_SIZE_not_cacheline_multiple);
+#define PERCPU_BAKERY_LOCK_SIZE (PLAT_PERCPU_BAKERY_LOCK_SIZE)
+#else
+/*
+ * Use the linker defined symbol which has evaluated the size reqiurement.
+ * This is not as efficient as using a platform defined constant
+ */
+IMPORT_SYM(uintptr_t, __PERCPU_BAKERY_LOCK_START__, BAKERY_LOCK_START);
+IMPORT_SYM(uintptr_t, __PERCPU_BAKERY_LOCK_END__, BAKERY_LOCK_END);
+#define PERCPU_BAKERY_LOCK_SIZE (BAKERY_LOCK_END - BAKERY_LOCK_START)
+#endif
+
+static inline bakery_lock_t *get_bakery_info(unsigned int cpu_ix,
+					     bakery_lock_t *lock)
+{
+	return (bakery_info_t *)((uintptr_t)lock +
+				cpu_ix * PERCPU_BAKERY_LOCK_SIZE);
+}
+
+static inline void write_cache_op(uintptr_t addr, bool cached)
+{
+	if (cached)
+		dccvac(addr);
+	else
+		dcivac(addr);
+
+	dsbish();
+}
+
+static inline void read_cache_op(uintptr_t addr, bool cached)
+{
+	if (cached)
+		dccivac(addr);
+
+	dmbish();
+}
+
+/* Helper function to check if the lock is acquired */
+static inline __unused bool is_lock_acquired(const bakery_info_t *my_bakery_info,
+				    bool is_cached)
+{
+	/*
+	 * Even though lock data is updated only by the owning cpu and
+	 * appropriate cache maintenance operations are performed,
+	 * if the previous update was done when the cpu was not participating
+	 * in coherency, then there is a chance that cache maintenance
+	 * operations were not propagated to all the caches in the system.
+	 * Hence do a `read_cache_op()` prior to read.
+	 */
+	read_cache_op((uintptr_t)my_bakery_info, is_cached);
+	return bakery_ticket_number(my_bakery_info->lock_data) != 0U;
+}
+
+static unsigned int bakery_get_ticket(bakery_lock_t *lock,
+				      unsigned int me, bool is_cached)
+{
+	unsigned int my_ticket, their_ticket;
+	unsigned int they;
+	bakery_info_t *my_bakery_info, *their_bakery_info;
+
+	/*
+	 * Obtain a reference to the bakery information for this cpu and ensure
+	 * it is not NULL.
+	 */
+	my_bakery_info = get_bakery_info(me, lock);
+	assert(my_bakery_info != NULL);
+
+	/* Prevent recursive acquisition.*/
+	assert(!is_lock_acquired(my_bakery_info, is_cached));
+
+	/*
+	 * Tell other contenders that we are through the bakery doorway i.e.
+	 * going to allocate a ticket for this cpu.
+	 */
+	my_ticket = 0U;
+	my_bakery_info->lock_data = make_bakery_data(CHOOSING_TICKET, my_ticket);
+
+	write_cache_op((uintptr_t)my_bakery_info, is_cached);
+
+	/*
+	 * Iterate through the bakery information of each contender to allocate
+	 * the highest ticket number for this cpu.
+	 */
+	for (they = 0U; they < BAKERY_LOCK_MAX_CPUS; they++) {
+		if (me == they)
+			continue;
+
+		/*
+		 * Get a reference to the other contender's bakery info and
+		 * ensure that a stale copy is not read.
+		 */
+		their_bakery_info = get_bakery_info(they, lock);
+		assert(their_bakery_info != NULL);
+
+		read_cache_op((uintptr_t)their_bakery_info, is_cached);
+
+		/*
+		 * Update this cpu's ticket number if a higher ticket number is
+		 * seen
+		 */
+		their_ticket = bakery_ticket_number(their_bakery_info->lock_data);
+		if (their_ticket > my_ticket)
+			my_ticket = their_ticket;
+	}
+
+	/*
+	 * Compute ticket; then signal to other contenders waiting for us to
+	 * finish calculating our ticket value that we're done
+	 */
+	++my_ticket;
+	my_bakery_info->lock_data = make_bakery_data(CHOSEN_TICKET, my_ticket);
+
+	write_cache_op((uintptr_t)my_bakery_info, is_cached);
+
+	return my_ticket;
+}
+
+void bakery_lock_get(bakery_lock_t *lock)
+{
+	unsigned int they, me;
+	unsigned int my_ticket, my_prio, their_ticket;
+	bakery_info_t *their_bakery_info;
+	unsigned int their_bakery_data;
+	bool is_cached;
+
+	me = plat_my_core_pos();
+	is_cached = is_dcache_enabled();
+
+	/* Get a ticket */
+	my_ticket = bakery_get_ticket(lock, me, is_cached);
+
+	/*
+	 * Now that we got our ticket, compute our priority value, then compare
+	 * with that of others, and proceed to acquire the lock
+	 */
+	my_prio = bakery_get_priority(my_ticket, me);
+	for (they = 0U; they < BAKERY_LOCK_MAX_CPUS; they++) {
+		if (me == they)
+			continue;
+
+		/*
+		 * Get a reference to the other contender's bakery info and
+		 * ensure that a stale copy is not read.
+		 */
+		their_bakery_info = get_bakery_info(they, lock);
+		assert(their_bakery_info != NULL);
+
+		/* Wait for the contender to get their ticket */
+		do {
+			read_cache_op((uintptr_t)their_bakery_info, is_cached);
+			their_bakery_data = their_bakery_info->lock_data;
+		} while (bakery_is_choosing(their_bakery_data));
+
+		/*
+		 * If the other party is a contender, they'll have non-zero
+		 * (valid) ticket value. If they do, compare priorities
+		 */
+		their_ticket = bakery_ticket_number(their_bakery_data);
+		if (their_ticket && (bakery_get_priority(their_ticket, they) < my_prio)) {
+			/*
+			 * They have higher priority (lower value). Wait for
+			 * their ticket value to change (either release the lock
+			 * to have it dropped to 0; or drop and probably content
+			 * again for the same lock to have an even higher value)
+			 */
+			do {
+				wfe();
+				read_cache_op((uintptr_t)their_bakery_info, is_cached);
+			} while (their_ticket
+				== bakery_ticket_number(their_bakery_info->lock_data));
+		}
+	}
+
+	/*
+	 * Lock acquired. Ensure that any reads and writes from a shared
+	 * resource in the critical section read/write values after the lock is
+	 * acquired.
+	 */
+	dmbish();
+}
+
+void bakery_lock_release(bakery_lock_t *lock)
+{
+	bakery_info_t *my_bakery_info;
+	bool is_cached = is_dcache_enabled();
+
+	my_bakery_info = get_bakery_info(plat_my_core_pos(), lock);
+
+	assert(is_lock_acquired(my_bakery_info, is_cached));
+
+	/*
+	 * Ensure that other observers see any stores in the critical section
+	 * before releasing the lock. Also ensure all loads in the critical
+	 * section are complete before releasing the lock. Release the lock by
+	 * resetting ticket. Then signal other waiting contenders.
+	 */
+	dmbish();
+	my_bakery_info->lock_data = 0U;
+	write_cache_op((uintptr_t)my_bakery_info, is_cached);
+
+	/* This sev is ordered by the dsbish in write_cahce_op */
+	sev();
+}