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SubjectRe: [PATCH 03/14] clocksource: Add ARM System timer driver
Am 12.02.2015 um 18:45 schrieb Maxime Coquelin:
> 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>;
> +};

Binding documentation is supposed to go into its own patch:
https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/tree/Documentation/devicetree/bindings/submitting-patches.txt

> 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);

I've used a SysTick based implementation on my stm32 branch myself, but
looking at efm32 I got the impression that it would be better to use one
of the 32-bit TIM2/TIM5 as clocksource and the other as clockevents?

Still this implementation will be handy to have, also for other targets.

Regards,
Andreas

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GF: Felix Imendörffer, Jane Smithard, Jennifer Guild, Dilip Upmanyu,
Graham Norton; HRB 21284 (AG Nürnberg)


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