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authorRaul E Rangel <rrangel@chromium.org>2018-08-20 12:54:58 -0600
committerMartin Roth <martinroth@google.com>2018-09-12 14:15:25 +0000
commit370c116ca5fa9e9d04ed61f445debde882b6a1cb (patch)
treea6862b96919b1eba74b551d31721960199420bdb
parentd63627fb846b6621be87348b1653a5f37070e12f (diff)
libpayload/x86/delay: Add an x86 arch_ndelay
This method has a pause instruction to help the CPU relax a little bit. Measuring grunt it saves about 80mW. BUG=b:109749762 TEST=Made sure that grunt boots. Change-Id: I045a941ed42fcc4f2dbdd65b5cbb42d84813f50c Signed-off-by: Raul E Rangel <rrangel@chromium.org> Reviewed-on: https://review.coreboot.org/28244 Reviewed-by: Martin Roth <martinroth@google.com> Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
-rw-r--r--payloads/libpayload/arch/x86/Makefile.inc1
-rw-r--r--payloads/libpayload/arch/x86/delay.c52
2 files changed, 53 insertions, 0 deletions
diff --git a/payloads/libpayload/arch/x86/Makefile.inc b/payloads/libpayload/arch/x86/Makefile.inc
index 268df1e542..0cc477399a 100644
--- a/payloads/libpayload/arch/x86/Makefile.inc
+++ b/payloads/libpayload/arch/x86/Makefile.inc
@@ -35,6 +35,7 @@ libc-y += timer.c coreboot.c util.S
libc-y += exec.S virtual.c
libc-y += selfboot.c
libc-y += exception_asm.S exception.c
+libc-y += delay.c
# Will fall back to default_memXXX() in libc/memory.c if GPL not allowed.
libc-$(CONFIG_LP_GPL) += string.c
diff --git a/payloads/libpayload/arch/x86/delay.c b/payloads/libpayload/arch/x86/delay.c
new file mode 100644
index 0000000000..541cf7a436
--- /dev/null
+++ b/payloads/libpayload/arch/x86/delay.c
@@ -0,0 +1,52 @@
+/*
+ * This file is part of the libpayload project.
+ *
+ * Copyright (C) 2018 Google LLC.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ * 3. The name of the author may not be used to endorse or promote products
+ * derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <libpayload.h>
+
+/* The pause instruction can delay 10-140 CPU cycles, so avoid calling it when
+ * getting close to finishing. Depending on the timer source, the timer can be
+ * running at CPU frequency, bus frequency, or some arbitrary value. We assume
+ * that the timer is running at the CPU frequency. */
+#define PAUSE_THRESHOLD_TICKS 150
+
+void arch_ndelay(uint64_t ns)
+{
+ uint64_t delta = ns * timer_hz() / NSECS_PER_SEC;
+ uint64_t pause_delta = 0;
+ uint64_t start = timer_raw_value();
+
+ if (delta > PAUSE_THRESHOLD_TICKS)
+ pause_delta = delta - PAUSE_THRESHOLD_TICKS;
+
+ while (timer_raw_value() - start < pause_delta)
+ asm volatile("pause\n\t");
+
+ while (timer_raw_value() - start < delta)
+ continue;
+}