Message-ID: <518A6099.8070505@gmail.com>
Date:	Wed, 08 May 2013 09:26:33 -0500
From:	Rob Herring <robherring2@...il.com>
To:	Srinivas KANDAGATLA <srinivas.kandagatla@...com>
CC:	linux@....linux.org.uk, will.deacon@....com,
	Rob Landley <rob@...dley.net>,
	Grant Likely <grant.likely@...retlab.ca>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>,
	Stuart Menefy <stuart.menefy@...com>,
	Shawn Guo <shawn.guo@...aro.org>,
	Olof Johansson <olof@...om.net>,
	Jason Cooper <jason@...edaemon.net>,
	Stephen Warren <swarren@...dia.com>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Nicolas Pitre <nico@...aro.org>,
	Dave Martin <dave.martin@...aro.org>,
	Marc Zyngier <marc.zyngier@....com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Arnd Bergmann <arnd@...db.de>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Dong Aisheng <dong.aisheng@...aro.org>,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	devicetree-discuss@...ts.ozlabs.org,
	linux-arm-kernel@...ts.infradead.org, linux-serial@...r.kernel.org
Subject: Re: [RFC 2/8] ARM:global_timer: Add ARM global timer support.

On 05/08/2013 09:11 AM, Srinivas KANDAGATLA wrote:
> From: Stuart Menefy <stuart.menefy@...com>
> 
> This is a simple driver for the global timer module found in the Cortex
> A9-MP cores from revision r1p0 onwards. This should be able to perform
> the functions of the system timer and the local timer in an SMP system.
> 
> The global timer has the following features:
>     The global timer is a 64-bit incrementing counter with an
> auto-incrementing feature. It continues incrementing after sending
> interrupts. The global timer is memory mapped in the private memory
> region.
>     The global timer is accessible to all Cortex-A9 processors in the
> cluster. Each Cortex-A9 processor has a private 64-bit comparator that
> is used to assert a private interrupt when the global timer has reached
> the comparator value. All the Cortex-A9 processors in a design use the
> banked ID, ID27, for this interrupt. ID27 is sent to the Interrupt
> Controller as a Private Peripheral Interrupt. The global timer is
> clocked by PERIPHCLK.

PERIPHCLK scales with cpu clock typically so the global timer is not a
suitable clocksource if you use cpufreq. You can deal with the scaling
on clockevents, but not a clocksource. I imagine the global timers is
also typically power-gated in some low power modes. This is why no one
has added support already. Are neither of those an issue or going to be
an issue for you?

Rob

> 
> Signed-off-by: Stuart Menefy <stuart.menefy@...com>
> Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@...com>
> ---
>  Documentation/devicetree/bindings/arm/gt.txt |   21 ++
>  arch/arm/Kconfig                             |    6 +
>  arch/arm/include/asm/global_timer.h          |   12 +
>  arch/arm/kernel/Makefile                     |    1 +
>  arch/arm/kernel/global_timer.c               |  325 ++++++++++++++++++++++++++
>  5 files changed, 365 insertions(+), 0 deletions(-)
>  create mode 100644 Documentation/devicetree/bindings/arm/gt.txt
>  create mode 100644 arch/arm/include/asm/global_timer.h
>  create mode 100644 arch/arm/kernel/global_timer.c
> 
> diff --git a/Documentation/devicetree/bindings/arm/gt.txt b/Documentation/devicetree/bindings/arm/gt.txt
> new file mode 100644
> index 0000000..4ec5fb0
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/arm/gt.txt
> @@ -0,0 +1,21 @@
> +
> +* ARM Global Timer
> +	Cortex-A9 are often associated with a per-core Global timer.
> +
> +** Timer node required properties:
> +
> +- compatible : Should be one of:
> +	"arm,cortex-a9-global-timer"
> +
> +- interrupts : One interrupt to each core
> +
> +- reg : Specify the base address and the size of the GT timer
> +	register window.
> +
> +Example:
> +
> +	gt-timer@...00600 {
> +		compatible = "arm,cortex-a9-global-timer";
> +		reg = <0x2c000600 0x20>;
> +		interrupts = <1 13 0xf01>;
> +	};
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index 1cacda4..c8c524e 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -1606,6 +1606,12 @@ config HAVE_ARM_TWD
>  	help
>  	  This options enables support for the ARM timer and watchdog unit
>  
> +config HAVE_ARM_GT
> +	bool
> +	select CLKSRC_OF if OF
> +	help
> +	  This options enables support for the ARM global timer unit
> +
>  choice
>  	prompt "Memory split"
>  	default VMSPLIT_3G
> diff --git a/arch/arm/include/asm/global_timer.h b/arch/arm/include/asm/global_timer.h
> new file mode 100644
> index 0000000..46f9188
> --- /dev/null
> +++ b/arch/arm/include/asm/global_timer.h
> @@ -0,0 +1,12 @@
> +/*
> + * arch/arm/include/asm/global_timer.h
> + *
> + * Copyright (C) 2013 STMicroelectronics (R&D) Limited.
> + * Author: Stuart Menefy <stuart.menefy@...com>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + */
> +
> +int __init global_timer_init(void __iomem *base, unsigned int timer_irq);
> diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
> index 5f3338e..af51808 100644
> --- a/arch/arm/kernel/Makefile
> +++ b/arch/arm/kernel/Makefile
> @@ -35,6 +35,7 @@ obj-$(CONFIG_ARM_CPU_SUSPEND)	+= sleep.o suspend.o
>  obj-$(CONFIG_SMP)		+= smp.o smp_tlb.o
>  obj-$(CONFIG_HAVE_ARM_SCU)	+= smp_scu.o
>  obj-$(CONFIG_HAVE_ARM_TWD)	+= smp_twd.o
> +obj-$(CONFIG_HAVE_ARM_GT)	+= global_timer.o
>  obj-$(CONFIG_ARM_ARCH_TIMER)	+= arch_timer.o
>  obj-$(CONFIG_DYNAMIC_FTRACE)	+= ftrace.o insn.o
>  obj-$(CONFIG_FUNCTION_GRAPH_TRACER)	+= ftrace.o insn.o
> diff --git a/arch/arm/kernel/global_timer.c b/arch/arm/kernel/global_timer.c
> new file mode 100644
> index 0000000..0ab1af3
> --- /dev/null
> +++ b/arch/arm/kernel/global_timer.c
> @@ -0,0 +1,325 @@
> +/*
> + * linux/arch/arm/kernel/global_timer.c
> + *
> + * Copyright (C) 2013 STMicroelectronics (R&D) Limited.
> + * Author: Stuart Menefy <stuart.menefy@...com>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + */
> +
> +#include <linux/init.h>
> +#include <linux/interrupt.h>
> +#include <linux/clocksource.h>
> +#include <linux/clockchips.h>
> +#include <linux/clk.h>
> +#include <linux/clkdev.h>
> +#include <linux/err.h>
> +#include <linux/io.h>
> +#include <linux/of.h>
> +#include <linux/of_irq.h>
> +#include <linux/of_address.h>
> +
> +#include <asm/mach/irq.h>
> +#include <asm/global_timer.h>
> +#include <asm/localtimer.h>
> +
> +#define GT_COUNTER0	0x00
> +#define GT_COUNTER1	0x04
> +
> +#define GT_CONTROL	0x08
> +#define GT_CONTROL_TIMER_ENABLE		BIT(0)
> +#define GT_CONTROL_COMP_ENABLE		BIT(1)	/* banked */
> +#define GT_CONTROL_IRQ_ENABLE		BIT(2)	/* banked */
> +#define GT_CONTROL_AUTO_INC		BIT(3)	/* banked */
> +
> +#define GT_INT_STATUS	0x0c
> +#define GT_INT_STATUS_EVENT_FLAG	BIT(0)
> +
> +#define GT_COMP0	0x10
> +#define GT_COMP1	0x14
> +#define GT_AUTO_INC	0x18
> +
> +/*
> + * We are expecting to be clocked by the ARM peripheral clock.
> + *
> + * Note: it is assumed we are using a prescaler value of zero, so this is
> + * the units for all operations.
> + */
> +static void __iomem *gt_base;
> +static struct clk *gt_clk;
> +static unsigned long gt_clk_rate;
> +static int gt_ppi;
> +static struct clock_event_device __percpu **gt_evt;
> +static DEFINE_PER_CPU(bool, percpu_init_called);
> +static DEFINE_PER_CPU(struct clock_event_device, gt_clockevent);
> +
> +union gt_counter {
> +	cycle_t cycles;
> +	struct {
> +		uint32_t lower;
> +		uint32_t upper;
> +	};
> +};
> +
> +static union gt_counter gt_counter_read(void)
> +{
> +	union gt_counter res;
> +	uint32_t upper;
> +
> +	upper = readl(gt_base + GT_COUNTER1);
> +	do {
> +		res.upper = upper;
> +		res.lower = readl(gt_base + GT_COUNTER0);
> +		upper = readl(gt_base + GT_COUNTER1);
> +	} while (upper != res.upper);
> +
> +	return res;
> +}
> +
> +static void gt_compare_set(unsigned long delta, int periodic)
> +{
> +	union gt_counter counter = gt_counter_read();
> +	unsigned long ctrl = readl(gt_base + GT_CONTROL);
> +
> +	BUG_ON(!(ctrl & GT_CONTROL_TIMER_ENABLE));
> +	BUG_ON(ctrl & (GT_CONTROL_COMP_ENABLE |
> +		       GT_CONTROL_IRQ_ENABLE |
> +		       GT_CONTROL_AUTO_INC));
> +
> +	counter.cycles += delta;
> +	writel(counter.lower, gt_base + GT_COMP0);
> +	writel(counter.upper, gt_base + GT_COMP1);
> +
> +	ctrl |= GT_CONTROL_COMP_ENABLE | GT_CONTROL_IRQ_ENABLE;
> +
> +	if (periodic) {
> +		writel(delta, gt_base + GT_AUTO_INC);
> +		ctrl |= GT_CONTROL_AUTO_INC;
> +	}
> +
> +	writel(ctrl, gt_base + GT_CONTROL);
> +}
> +
> +static void gt_clockevent_set_mode(enum clock_event_mode mode,
> +				   struct clock_event_device *clk)
> +{
> +	switch (mode) {
> +	case CLOCK_EVT_MODE_PERIODIC:
> +		gt_compare_set(gt_clk_rate/HZ, 1);
> +		break;
> +	case CLOCK_EVT_MODE_ONESHOT:
> +		/* period set, and timer enabled in 'next_event' hook */
> +		BUG_ON(readl(gt_base + GT_CONTROL) &
> +		       (GT_CONTROL_COMP_ENABLE |
> +			GT_CONTROL_IRQ_ENABLE |
> +			GT_CONTROL_AUTO_INC));
> +		/* Fall through */
> +	case CLOCK_EVT_MODE_UNUSED:
> +	case CLOCK_EVT_MODE_SHUTDOWN:
> +	default:
> +		writel(GT_CONTROL_TIMER_ENABLE, gt_base + GT_CONTROL);
> +		break;
> +	}
> +}
> +
> +static int gt_clockevent_set_next_event(unsigned long evt,
> +					struct clock_event_device *unused)
> +{
> +	gt_compare_set(evt, 0);
> +	return 0;
> +}
> +
> +static irqreturn_t gt_clockevent_interrupt(int irq, void *dev_id)
> +{
> +	struct clock_event_device *evt = *(struct clock_event_device **)dev_id;
> +
> +	writel(GT_INT_STATUS_EVENT_FLAG, gt_base + GT_INT_STATUS);
> +	evt->event_handler(evt);
> +
> +	return IRQ_HANDLED;
> +}
> +
> +static int __cpuinit gt_clockevents_init(struct clock_event_device *clk)
> +{
> +	struct clock_event_device **this_cpu_clk;
> +	int cpu = smp_processor_id();
> +
> +	clk->name = "Global Timer CE";
> +	clk->features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT;
> +	clk->set_mode = gt_clockevent_set_mode;
> +	clk->set_next_event = gt_clockevent_set_next_event;
> +	this_cpu_clk = __this_cpu_ptr(gt_evt);
> +	*this_cpu_clk = clk;
> +	clk->irq = gt_ppi;
> +	clockevents_config_and_register(clk, gt_clk_rate,
> +					0xf, 0xffffffff);
> +	per_cpu(percpu_init_called, cpu) = true;
> +	enable_percpu_irq(clk->irq, IRQ_TYPE_NONE);
> +	return 0;
> +}
> +
> +static void gt_clockevents_stop(struct clock_event_device *clk)
> +{
> +	gt_clockevent_set_mode(CLOCK_EVT_MODE_UNUSED, clk);
> +	disable_percpu_irq(clk->irq);
> +}
> +
> +static int __cpuinit gt_clockevents_setup(struct clock_event_device *clk)
> +{
> +	int cpu = smp_processor_id();
> +
> +	/* Use existing clock_event for boot cpu */
> +	if (per_cpu(percpu_init_called, cpu))
> +		return 0;
> +
> +	writel(0, gt_base + GT_CONTROL);
> +	writel(0, gt_base + GT_COUNTER0);
> +	writel(0, gt_base + GT_COUNTER1);
> +	writel(GT_CONTROL_TIMER_ENABLE, gt_base + GT_CONTROL);
> +
> +	return gt_clockevents_init(clk);
> +}
> +
> +static cycle_t gt_clocksource_read(struct clocksource *cs)
> +{
> +	union gt_counter res = gt_counter_read();
> +	return res.cycles;
> +}
> +
> +static struct clocksource gt_clocksource = {
> +	.name	= "Global Timer CS",
> +	.rating	= 300,
> +	.read	= gt_clocksource_read,
> +	.mask	= CLOCKSOURCE_MASK(64),
> +	.flags	= CLOCK_SOURCE_IS_CONTINUOUS,
> +};
> +
> +static void __init gt_clocksource_init(void)
> +{
> +	writel(0, gt_base + GT_CONTROL);
> +	writel(0, gt_base + GT_COUNTER0);
> +	writel(0, gt_base + GT_COUNTER1);
> +	writel(GT_CONTROL_TIMER_ENABLE, gt_base + GT_CONTROL);
> +
> +	gt_clocksource.shift = 20;
> +	gt_clocksource.mult =
> +		clocksource_hz2mult(gt_clk_rate, gt_clocksource.shift);
> +	clocksource_register(&gt_clocksource);
> +}
> +
> +static struct clk *gt_get_clock(void)
> +{
> +	struct clk *clk;
> +	int err;
> +
> +	clk = clk_get_sys("gt", NULL);
> +	if (IS_ERR(clk)) {
> +		pr_err("global-timer: clock not found: %ld\n", PTR_ERR(clk));
> +		return clk;
> +	}
> +
> +	err = clk_prepare_enable(clk);
> +	if (err) {
> +		pr_err("global-timer: clock prepare+enable failed: %d\n", err);
> +		clk_put(clk);
> +		return ERR_PTR(err);
> +	}
> +
> +	return clk;
> +}
> +
> +static struct local_timer_ops gt_lt_ops __cpuinitdata = {
> +	.setup	= gt_clockevents_setup,
> +	.stop	= gt_clockevents_stop,
> +};
> +
> +int __init global_timer_init(void __iomem *base, unsigned int timer_irq)
> +{
> +	unsigned int cpu = smp_processor_id();
> +	struct clock_event_device *evt = &per_cpu(gt_clockevent, cpu);
> +	int err = 0;
> +
> +	if (gt_base) {
> +		pr_warn("global-timer: invalid base address\n");
> +		return -EINVAL;
> +	}
> +
> +	gt_clk = gt_get_clock();
> +	if (IS_ERR(gt_clk)) {
> +		pr_warn("global-timer: clk not found\n");
> +		return -EINVAL;
> +	}
> +
> +	gt_evt = alloc_percpu(struct clock_event_device *);
> +	if (!gt_evt) {
> +		pr_warn("global-timer: can't allocate memory\n");
> +		return -ENOMEM;
> +	}
> +
> +	err = request_percpu_irq(timer_irq, gt_clockevent_interrupt,
> +				 "gt", gt_evt);
> +	if (err) {
> +		pr_warn("global-timer: can't register interrupt %d (%d)\n",
> +			timer_irq, err);
> +		goto out_free;
> +	}
> +
> +	gt_base = base;
> +	gt_clk_rate = clk_get_rate(gt_clk);
> +
> +	evt->irq = timer_irq;
> +	gt_ppi = timer_irq;
> +	evt->cpumask = cpumask_of(cpu);
> +
> +	gt_clocksource_init();
> +	gt_clockevents_init(evt);
> +	err =  local_timer_register(&gt_lt_ops);
> +	if (err) {
> +		pr_warn("global-timer: unable to register local timer.\n");
> +		goto out_irq;
> +	}
> +
> +	return 0;
> +
> +out_irq:
> +	free_percpu_irq(timer_irq, gt_evt);
> +out_free:
> +	free_percpu(gt_evt);
> +	return err;
> +}
> +
> +#ifdef CONFIG_OF
> +static void __init global_timer_of_register(struct device_node *np)
> +{
> +	struct clk *clk;
> +	int err = 0;
> +	int gt_ppi;
> +	static void __iomem *gt_base;
> +
> +	gt_ppi = irq_of_parse_and_map(np, 0);
> +	if (!gt_ppi) {
> +		err = -EINVAL;
> +		goto out;
> +	}
> +
> +	gt_base = of_iomap(np, 0);
> +	if (!gt_base) {
> +		err = -ENOMEM;
> +		goto out;
> +	}
> +
> +	clk = of_clk_get(np, 0);
> +	if (!IS_ERR(clk))
> +		clk_register_clkdev(clk, NULL, "gt");
> +
> +	global_timer_init(gt_base, gt_ppi);
> +
> +out:
> +	WARN(err, "Global timer register failed (%d)\n", err);
> +}
> +
> +CLOCKSOURCE_OF_DECLARE(arm_gt_a9, "arm,cortex-a9-global-timer",
> +			global_timer_of_register);
> +#endif
> 

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