[v6,04/15] clocksource/drivers: Add ARM System timer driver

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

Tested-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Maxime Coquelin <mcoquelin.stm32@gmail.com>
---
 drivers/clocksource/Kconfig          |  7 ++++
 drivers/clocksource/Makefile         |  1 +
 drivers/clocksource/armv7m_systick.c | 79 ++++++++++++++++++++++++++++++++++++
 3 files changed, 87 insertions(+)
 create mode 100644 drivers/clocksource/armv7m_systick.c

On 04/07/2015 06:30 PM, Maxime Coquelin wrote:
> This patch adds clocksource support for ARMv7-M's System timer,
> also known as SysTick.
>
> Tested-by: Chanwoo Choi <cw00.choi@samsung.com>
> Signed-off-by: Maxime Coquelin <mcoquelin.stm32@gmail.com>

Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>

> ---
>   drivers/clocksource/Kconfig          |  7 ++++
>   drivers/clocksource/Makefile         |  1 +
>   drivers/clocksource/armv7m_systick.c | 79 ++++++++++++++++++++++++++++++++++++
>   3 files changed, 87 insertions(+)
>   create mode 100644 drivers/clocksource/armv7m_systick.c
>
> diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
> index 1c2506f..b82e58b 100644
> --- a/drivers/clocksource/Kconfig
> +++ b/drivers/clocksource/Kconfig
> @@ -134,6 +134,13 @@ 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 752d5c7..1c9a643 100644
> --- a/drivers/clocksource/Makefile
> +++ b/drivers/clocksource/Makefile
> @@ -44,6 +44,7 @@ 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..addfd2c
> --- /dev/null
> +++ b/drivers/clocksource/armv7m_systick.c
> @@ -0,0 +1,79 @@
> +/*
> + * 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 = NULL;
> +	void __iomem *base;
> +	u32 rate;
> +	int ret;
> +
> +	base = of_iomap(np, 0);
> +	if (!base) {
> +		pr_warn("system-timer: invalid base address\n");
> +		return;
> +	}
> +
> +	ret = of_property_read_u32(np, "clock-frequency", &rate);
> +	if (ret) {
> +		clk = of_clk_get(np, 0);
> +		if (IS_ERR(clk))
> +			goto out_unmap;
> +
> +		ret = clk_prepare_enable(clk);
> +		if (ret)
> +			goto out_clk_put;
> +
> +		rate = clk_get_rate(clk);
> +		if (!rate)
> +			goto out_clk_disable;
> +	}
> +
> +	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);
> +		if (clk)
> +			goto out_clk_disable;
> +		else
> +			goto out_unmap;
> +	}
> +
> +	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);
> +	pr_warn("ARM System timer register failed (%d)\n", ret);
> +}
> +
> +CLOCKSOURCE_OF_DECLARE(arm_systick, "arm,armv7m-systick",
> +			system_timer_of_register);
>