This patch adds clocksource support for ARMv7-M's System timer,
also known as SysTick.

Signed-off-by: Maxime Coquelin <redacted>
---
 .../devicetree/bindings/arm/system_timer.txt       | 15 +++++
 drivers/clocksource/Kconfig                        |  7 ++
 drivers/clocksource/Makefile                       |  1 +
 drivers/clocksource/arm_system_timer.c             | 74 ++++++++++++++++++++++
 4 files changed, 97 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/arm/system_timer.txt
 create mode 100644 drivers/clocksource/arm_system_timer.c

diff --git a/Documentation/devicetree/bindings/arm/system_timer.txt b/Documentation/devicetree/bindings/arm/system_timer.txt
new file mode 100644
index 0000000..35268b7
--- /dev/null
+++ b/Documentation/devicetree/bindings/arm/system_timer.txt

@@ -0,0 +1,15 @@
+* ARM System Timer
+
+ARMv7-M includes a system timer, known as SysTick. Current driver only
+implements the clocksource feature.
+
+Required properties:
+- compatible : Should be "arm,armv7m-systick"
+- reg	     : The address range of the timer
+- clocks     : The input clock of the timer
+
+systick: system-timer {
+	compatible = "arm,armv7m-systick";
+	reg = <0xe000e010 0x10>;
+	clocks = <&clk_systick>;
+};

diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
index fc01ec2..f9fe4ac 100644
--- a/drivers/clocksource/Kconfig
+++ b/drivers/clocksource/Kconfig

@@ -124,6 +124,13 @@ config CLKSRC_ARM_GLOBAL_TIMER_SCHED_CLOCK
 	help
 	 Use ARM global timer clock source as sched_clock
 
+config ARM_SYSTEM_TIMER
+	bool
+	select CLKSRC_OF if OF
+	select CLKSRC_MMIO
+	help
+	  This options enables support for the ARM system timer unit
+
 config ATMEL_PIT
 	select CLKSRC_OF if OF
 	def_bool SOC_AT91SAM9 || SOC_SAMA5

diff --git a/drivers/clocksource/Makefile b/drivers/clocksource/Makefile
index 94d90b2..194400b 100644
--- a/drivers/clocksource/Makefile
+++ b/drivers/clocksource/Makefile

@@ -42,6 +42,7 @@ obj-$(CONFIG_MTK_TIMER)		+= mtk_timer.o
 
 obj-$(CONFIG_ARM_ARCH_TIMER)		+= arm_arch_timer.o
 obj-$(CONFIG_ARM_GLOBAL_TIMER)		+= arm_global_timer.o
+obj-$(CONFIG_ARM_SYSTEM_TIMER)		+= arm_system_timer.o
 obj-$(CONFIG_CLKSRC_METAG_GENERIC)	+= metag_generic.o
 obj-$(CONFIG_ARCH_HAS_TICK_BROADCAST)	+= dummy_timer.o
 obj-$(CONFIG_ARCH_KEYSTONE)		+= timer-keystone.o

diff --git a/drivers/clocksource/arm_system_timer.c b/drivers/clocksource/arm_system_timer.c
new file mode 100644
index 0000000..69e6ef9
--- /dev/null
+++ b/drivers/clocksource/arm_system_timer.c

@@ -0,0 +1,74 @@
+/*
+ * Copyright (C) Maxime Coquelin 2015
+ * Author:  Maxime Coquelin <mcoquelin.stm32-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
+ * License terms:  GNU General Public License (GPL), version 2
+ */
+
+#include <linux/kernel.h>
+#include <linux/clocksource.h>
+#include <linux/clockchips.h>
+#include <linux/of.h>
+#include <linux/of_address.h>
+#include <linux/clk.h>
+#include <linux/bitops.h>
+
+#define SYST_CSR	0x00
+#define SYST_RVR	0x04
+#define SYST_CVR	0x08
+#define SYST_CALIB	0x0c
+
+#define SYST_CSR_ENABLE BIT(0)
+
+#define SYSTICK_LOAD_RELOAD_MASK 0x00FFFFFF
+
+static void __init system_timer_of_register(struct device_node *np)
+{
+	struct clk *clk;
+	void __iomem *base;
+	unsigned long rate;
+	int ret;
+
+	base = of_iomap(np, 0);
+	if (!base) {
+		pr_warn("system-timer: invalid base address\n");
+		return;
+	}
+
+	clk = of_clk_get(np, 0);
+	if (IS_ERR(clk)) {
+		pr_warn("system-timer: clk not found\n");
+		ret = PTR_ERR(clk);
+		goto out_unmap;
+	}
+
+	ret = clk_prepare_enable(clk);
+	if (ret)
+		goto out_clk_put;
+
+	rate = clk_get_rate(clk);
+
+	writel_relaxed(SYSTICK_LOAD_RELOAD_MASK, base + SYST_RVR);
+	writel_relaxed(SYST_CSR_ENABLE, base + SYST_CSR);
+
+	ret = clocksource_mmio_init(base + SYST_CVR, "arm_system_timer", rate,
+			200, 24, clocksource_mmio_readl_down);
+	if (ret) {
+		pr_err("failed to init clocksource (%d)\n", ret);
+		goto out_clk_disable;
+	}
+
+	pr_info("ARM System timer initialized as clocksource\n");
+
+	return;
+
+out_clk_disable:
+	clk_disable_unprepare(clk);
+out_clk_put:
+	clk_put(clk);
+out_unmap:
+	iounmap(base);
+	WARN(ret, "ARM System timer register failed (%d)\n", ret);
+}
+
+CLOCKSOURCE_OF_DECLARE(arm_systick, "arm,armv7m-systick",
+			system_timer_of_register);