clocksource: add ARMv7-M SysTick driver

The SysTick is a simple 24-bit system timer that's required for ARMv7-M
implementations. Add a clocksource driver for it for Cortex-M system
support.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Link: https://lore.barebox.org/20220131081146.1883859-1-a.fatoum@pengutronix.de
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

3 files changed, 93 insertions, 0 deletions

diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
index c6ca72d4e9..9fae1f2d35 100644
--- a/drivers/clocksource/Kconfig
+++ b/drivers/clocksource/Kconfig
@@ -115,4 +115,9 @@ config CLINT_TIMER
 	  This option enables the CLINT timer for RISC-V systems.  The CLINT
 	  driver is usually used for NoMMU RISC-V systems.
 
+config ARMV7M_SYSTICK
+	bool "Support for the ARMv7M system timer" if COMPILE_TEST
+	help
+	  This option enables support for the ARMv7M system timer unit.
+
 endmenu
diff --git a/drivers/clocksource/Makefile b/drivers/clocksource/Makefile
index 21fd83a093..a4a7b84fae 100644
--- a/drivers/clocksource/Makefile
+++ b/drivers/clocksource/Makefile
@@ -24,3 +24,4 @@ obj-$(CONFIG_CLOCKSOURCE_TI_DM) += timer-ti-dm.o
 obj-$(CONFIG_CLOCKSOURCE_TI_32K) += timer-ti-32k.o
 obj-$(CONFIG_CLINT_TIMER) += timer-clint.o
 obj-$(CONFIG_RISCV_TIMER) += timer-riscv.o
+obj-$(CONFIG_ARMV7M_SYSTICK) += armv7m_systick.o
diff --git a/drivers/clocksource/armv7m_systick.c b/drivers/clocksource/armv7m_systick.c
new file mode 100644
index 0000000000..5f9222c50b
--- /dev/null
+++ b/drivers/clocksource/armv7m_systick.c
@@ -0,0 +1,87 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) Maxime Coquelin 2015
+ * Author:  Maxime Coquelin <mcoquelin.stm32@gmail.com>
+ */
+
+#include <common.h>
+#include <init.h>
+#include <clock.h>
+#include <io.h>
+#include <linux/clk.h>
+#include <linux/err.h>
+
+#define SYST_CSR	0x00
+#define SYST_RVR	0x04
+#define SYST_CVR	0x08
+#define SYST_CALIB	0x0c
+
+#define SYSTICK_CTRL_EN		BIT(0)
+/* Clock source: 0 = Ref clock, 1 = CPU clock */
+#define SYSTICK_CTRL_CPU_CLK	BIT(2)
+#define SYSTICK_CAL_NOREF	BIT(31)
+
+#define SYSTICK_LOAD_RELOAD_MASK 0x00FFFFFF
+
+static __iomem void *systick_base;
+
+static u64 armv7m_systick_clocksource_read(void)
+{
+        return SYSTICK_LOAD_RELOAD_MASK - readl(systick_base + SYST_CVR);
+}
+
+static struct clocksource cs = {
+	.read	= armv7m_systick_clocksource_read,
+	.mask	= CLOCKSOURCE_MASK(24),
+	.shift	= 0,
+};
+
+static int armv7m_systick_probe(struct device_d *dev)
+{
+	struct clk *clk = NULL;
+	u32 rate, cal;
+	int ret;
+
+	systick_base = dev_request_mem_region_err_null(dev, 0);
+	if (!systick_base)
+		return -ENOENT;
+
+	ret = of_property_read_u32(dev->device_node, "clock-frequency", &rate);
+	if (ret) {
+		clk = clk_get(dev, NULL);
+		if (IS_ERR(clk))
+			return PTR_ERR(clk);
+
+		ret = clk_enable(clk);
+		if (ret)
+			return ret;
+
+		rate = clk_get_rate(clk);
+		if (!rate)
+			return -EINVAL;
+	}
+
+	writel_relaxed(SYSTICK_LOAD_RELOAD_MASK, systick_base + SYST_RVR);
+
+	cal = readl(&systick_base + SYST_CALIB);
+	if (cal & SYSTICK_CAL_NOREF)
+		writel(SYSTICK_CTRL_EN | SYSTICK_CTRL_CPU_CLK, systick_base + SYST_CSR);
+	else
+		writel(SYSTICK_CTRL_EN, systick_base + SYST_CSR);
+
+	cs.mult = clocksource_hz2mult(rate, cs.shift);
+
+	return init_clock(&cs);
+}
+
+static struct of_device_id armv7m_systick_dt_ids[] = {
+	{ .compatible = "arm,armv7m-systick", },
+	{ }
+};
+
+static struct driver_d armv7m_systick_driver = {
+	.name = "armv7m-systick-timer",
+	.probe = armv7m_systick_probe,
+	.of_compatible = DRV_OF_COMPAT(armv7m_systick_dt_ids),
+};
+postcore_platform_driver(armv7m_systick_driver);