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    Subject[PATCH v2 04/18] clocksource: Add ARM System timer driver
    Date
    This patch adds clocksource support for ARMv7-M's System timer,
    also known as SysTick.

    Signed-off-by: Maxime Coquelin <mcoquelin.stm32@gmail.com>
    ---
    drivers/clocksource/Kconfig | 7 ++++
    drivers/clocksource/Makefile | 1 +
    drivers/clocksource/armv7m_systick.c | 78 ++++++++++++++++++++++++++++++++++++
    3 files changed, 86 insertions(+)
    create mode 100644 drivers/clocksource/armv7m_systick.c

    diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
    index fc01ec2..fb6011e 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 ARMV7M_SYSTICK
    + bool
    + select CLKSRC_OF if OF
    + select CLKSRC_MMIO
    + help
    + This options enables support for the ARMv7M 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..eeea736 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-$(CONFIG_ARMV7M_SYSTICK) += armv7m_systick.o
    obj-$(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/armv7m_systick.c b/drivers/clocksource/armv7m_systick.c
    new file mode 100644
    index 0000000..23d8249
    --- /dev/null
    +++ b/drivers/clocksource/armv7m_systick.c
    @@ -0,0 +1,78 @@
    +/*
    + * Copyright (C) Maxime Coquelin 2015
    + * Author: Maxime Coquelin <mcoquelin.stm32@gmail.com>
    + * 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;
    + u32 rate = 0;
    + 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)) {
    + ret = clk_prepare_enable(clk);
    + if (ret) {
    + clk_put(clk);
    + goto out_unmap;
    + }
    +
    + rate = clk_get_rate(clk);
    + }
    +
    + /* If no clock found, try to get clock-frequency property */
    + if (!rate) {
    + ret = of_property_read_u32(np, "clock-frequency", &rate);
    + if (ret)
    + goto out_unmap;
    + }
    +
    + 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:
    + if (!IS_ERR(clk))
    + clk_disable_unprepare(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);
    --
    1.9.1


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