[PATCH 03/14] clocksource: Add ARM System timer driver

[Rob Herring]

On Thu, Feb 12, 2015 at 11:45 AM, Maxime Coquelin
<mcoquelin.stm32 at gmail.com> wrote:
> This patch adds clocksource support for ARMv7-M's System timer,
> also known as SysTick.
>
> Signed-off-by: Maxime Coquelin <mcoquelin.stm32 at gmail.com>
> ---
>  .../devicetree/bindings/arm/system_timer.txt       | 15 +++++

Please include v7M in the name. System timer sounds very generic. This
is the only timer architecturally defined IIRC, so perhaps just
"armv7m_systick".

>  drivers/clocksource/Kconfig                        |  7 ++
>  drivers/clocksource/Makefile                       |  1 +
>  drivers/clocksource/arm_system_timer.c             | 74 ++++++++++++++++++++++

Same here.


>  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

You may want to consider supporting "clock-frequency" here too. In
more simple chips you may just have fixed clocks and may want to run a
kernel with COMMON_CLK disabled for size savings.

> +
> +systick: system-timer {

This should be "systick: timer at e000e010".

Same for your dts file.

> +       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 at 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
>