[PATCH v2] clocksource: add dummy software-only clocksource

[Antony Pavlov]

This driver is very handy for initial barebox porting.
It was used for running barebox on DiGiC2-based camera
and initial porting barebox to Loongson-1 and ar9331.

Signed-off-by: Antony Pavlov <antonynpavlov at gmail.com>
Signed-off-by: Sascha Hauer <s.hauer at pengutronix.de>
Reported-by: Alexander Aring <alex.aring at gmail.com>
Reported-by: Alexander Shiyan <shc_work at mail.ru>
---
 drivers/clocksource/Kconfig  | 22 +++++++++++++++++
 drivers/clocksource/Makefile |  1 +
 drivers/clocksource/dummy.c  | 56 ++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 79 insertions(+)
 create mode 100644 drivers/clocksource/dummy.c

diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
index 4ef25ec..f53c933 100644
--- a/drivers/clocksource/Kconfig
+++ b/drivers/clocksource/Kconfig
@@ -14,6 +14,28 @@ config CLOCKSOURCE_CLPS711X
 	bool
 	depends on ARCH_CLPS711X
 
+config CLOCKSOURCE_DUMMY
+	bool "Enable dummy software-only clocksource"
+	help
+	  When porting barebox to a new SoC there might be a case
+	  of broken or absent clocksource. This causes barebox serial
+	  console to be non functional.
+	  To solve the problem this software-only clocksource driver is used.
+	      WARNING!!! This clocksource doesn't provide correct timing.
+	  To adjust this clocksource please use CONFIG_CLOCKSOURCE_DUMMY_RATE.
+	  The bigger rate valuest makes clocksource "faster".
+	  It's possible to add this clocksource unconditionally.
+	  This clocksource starts very early (pure_initcall) so
+	  real clocksource will take over.
+	  This can help if initialization order is wrong so that
+	  the time functions are used before the real clocksource
+	  was initialized.
+
+config CLOCKSOURCE_DUMMY_RATE
+	int "  dummy clocksource rate"
+	depends on CLOCKSOURCE_DUMMY
+	default 1000
+
 config CLOCKSOURCE_MVEBU
 	bool
 	depends on ARCH_MVEBU
diff --git a/drivers/clocksource/Makefile b/drivers/clocksource/Makefile
index 25b7f46..834a15d 100644
--- a/drivers/clocksource/Makefile
+++ b/drivers/clocksource/Makefile
@@ -2,6 +2,7 @@ obj-$(CONFIG_AMBA_SP804) += amba-sp804.o
 obj-$(CONFIG_ARM_SMP_TWD) += arm_smp_twd.o
 obj-$(CONFIG_CLOCKSOURCE_BCM2835) += bcm2835.o
 obj-$(CONFIG_CLOCKSOURCE_CLPS711X) += clps711x.o
+obj-$(CONFIG_CLOCKSOURCE_DUMMY)   += dummy.o
 obj-$(CONFIG_CLOCKSOURCE_MVEBU)   += mvebu.o
 obj-$(CONFIG_CLOCKSOURCE_NOMADIK) += nomadik.o
 obj-$(CONFIG_CLOCKSOURCE_ORION)   += orion.o
diff --git a/drivers/clocksource/dummy.c b/drivers/clocksource/dummy.c
new file mode 100644
index 0000000..154a8cd
--- /dev/null
+++ b/drivers/clocksource/dummy.c
@@ -0,0 +1,56 @@
+/*
+ * Copyright (C) 2013 Antony Pavlov <antonynpavlov at gmail.com>
+ *
+ * This file is part of barebox.
+ * See file CREDITS for list of people who contributed to this project.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2
+ * as published by the Free Software Foundation.
+ *
+ * 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.  See the
+ * GNU General Public License for more details.
+ *
+ */
+
+#include <common.h>
+#include <init.h>
+#include <clock.h>
+
+static uint64_t dummy_counter;
+
+static uint64_t dummy_cs_read(void)
+{
+	static int first;
+
+	if (!first) {
+		pr_warn("Warning: Using dummy clocksource\n");
+		first = 1;
+	}
+
+	dummy_counter += CONFIG_CLOCKSOURCE_DUMMY_RATE;
+
+	return dummy_counter;
+}
+
+static struct clocksource dummy_cs = {
+	.read	= dummy_cs_read,
+	.mask   = CLOCKSOURCE_MASK(32),
+};
+
+static int clocksource_init(void)
+{
+	dummy_counter = 0;
+
+	clocks_calc_mult_shift(&dummy_cs.mult, &dummy_cs.shift,
+		100000000, NSEC_PER_SEC, 10);
+
+	pr_debug("clocksource_init: mult=%08x, shift=%08x\n",
+			dummy_cs.mult, dummy_cs.shift);
+	init_clock(&dummy_cs);
+
+	return 0;
+}
+pure_initcall(clocksource_init);
-- 
1.9.0