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    Subject[PATCH 03/14] 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>
    ---
    .../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@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;
    + 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);
    --
    1.9.1


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