From 8e4bff4cab0ddac6060645b0715210484d02ff40 Mon Sep 17 00:00:00 2001
From: Yuval Adam <_@yuv.al>
Date: Wed, 30 Aug 2017 08:25:59 +0000
Subject: Initial file dump from open source release

---
 arch/tile/lib/spinlock_common.h | 64 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 64 insertions(+)
 create mode 100644 arch/tile/lib/spinlock_common.h

(limited to 'arch/tile/lib/spinlock_common.h')

diff --git a/arch/tile/lib/spinlock_common.h b/arch/tile/lib/spinlock_common.h
new file mode 100644
index 00000000..6ac37509
--- /dev/null
+++ b/arch/tile/lib/spinlock_common.h
@@ -0,0 +1,64 @@
+/*
+ * Copyright 2010 Tilera Corporation. All Rights Reserved.
+ *
+ *   This program is free software; you can redistribute it and/or
+ *   modify it under the terms of the GNU General Public License
+ *   as published by the Free Software Foundation, version 2.
+ *
+ *   This program is distributed in the hope that it will be useful, but
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
+ *   NON INFRINGEMENT.  See the GNU General Public License for
+ *   more details.
+ * This file is included into spinlock_32.c or _64.c.
+ */
+
+/*
+ * The mfspr in __spinlock_relax() is 5 or 6 cycles plus 2 for loop
+ * overhead.
+ */
+#ifdef __tilegx__
+#define CYCLES_PER_RELAX_LOOP 7
+#else
+#define CYCLES_PER_RELAX_LOOP 8
+#endif
+
+/*
+ * Idle the core for CYCLES_PER_RELAX_LOOP * iterations cycles.
+ */
+static inline void
+relax(int iterations)
+{
+	for (/*above*/; iterations > 0; iterations--)
+		__insn_mfspr(SPR_PASS);
+	barrier();
+}
+
+/* Perform bounded exponential backoff.*/
+static void delay_backoff(int iterations)
+{
+	u32 exponent, loops;
+
+	/*
+	 * 2^exponent is how many times we go around the loop,
+	 * which takes 8 cycles.  We want to start with a 16- to 31-cycle
+	 * loop, so we need to go around minimum 2 = 2^1 times, so we
+	 * bias the original value up by 1.
+	 */
+	exponent = iterations + 1;
+
+	/*
+	 * Don't allow exponent to exceed 7, so we have 128 loops,
+	 * or 1,024 (to 2,047) cycles, as our maximum.
+	 */
+	if (exponent > 8)
+		exponent = 8;
+
+	loops = 1 << exponent;
+
+	/* Add a randomness factor so two cpus never get in lock step. */
+	loops += __insn_crc32_32(stack_pointer, get_cycles_low()) &
+		(loops - 1);
+
+	relax(loops);
+}
-- 
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