Message-ID: <20160926210716.GA12855@brightrain.aerifal.cx>
Date:   Mon, 26 Sep 2016 17:07:16 -0400
From:   Rich Felker <dalias@...c.org>
To:     devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-sh@...r.kernel.org
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH v7 2/2] clocksource: add J-Core timer/clocksource driver

Ping. Is there anything that still needs to be changed for this driver
to be acceptable?

On Mon, Sep 17, 2001 at 04:00:00AM +0000, Rich Felker wrote:
> At the hardware level, the J-Core PIT is integrated with the interrupt
> controller, but it is represented as its own device and has an
> independent programming interface. It provides a 12-bit countdown
> timer, which is not presently used, and a periodic timer. The interval
> length for the latter is programmable via a 32-bit throttle register
> whose units are determined by a bus-period register. The periodic
> timer is used to implement both periodic and oneshot clock event
> modes; in oneshot mode the interrupt handler simply disables the timer
> as soon as it fires.
> 
> Despite its device tree node representing an interrupt for the PIT,
> the actual irq generated is programmable, not hard-wired. The driver
> is responsible for programming the PIT to generate the hardware irq
> number that the DT assigns to it.
> 
> On SMP configurations, J-Core provides cpu-local instances of the PIT;
> no broadcast timer is needed. This driver supports the creation of the
> necessary per-cpu clock_event_device instances.
> 
> A nanosecond-resolution clocksource is provided using the J-Core "RTC"
> registers, which give a 64-bit seconds count and 32-bit nanoseconds
> that wrap every second. The driver converts these to a full-range
> 32-bit nanoseconds count.
> 
> Signed-off-by: Rich Felker <dalias@...c.org>
> ---
>  drivers/clocksource/Kconfig     |  10 ++
>  drivers/clocksource/Makefile    |   1 +
>  drivers/clocksource/jcore-pit.c | 240 ++++++++++++++++++++++++++++++++++++++++
>  include/linux/cpuhotplug.h      |   1 +
>  4 files changed, 252 insertions(+)
>  create mode 100644 drivers/clocksource/jcore-pit.c
> 
> diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
> index 5677886..95dd78b 100644
> --- a/drivers/clocksource/Kconfig
> +++ b/drivers/clocksource/Kconfig
> @@ -407,6 +407,16 @@ config SYS_SUPPORTS_SH_TMU
>  config SYS_SUPPORTS_EM_STI
>          bool
>  
> +config CLKSRC_JCORE_PIT
> +	bool "J-Core PIT timer driver"
> +	depends on OF && (SUPERH || COMPILE_TEST)
> +	depends on GENERIC_CLOCKEVENTS
> +	depends on HAS_IOMEM
> +	select CLKSRC_MMIO
> +	help
> +	  This enables build of clocksource and clockevent driver for
> +	  the integrated PIT in the J-Core synthesizable, open source SoC.
> +
>  config SH_TIMER_CMT
>  	bool "Renesas CMT timer driver" if COMPILE_TEST
>  	depends on GENERIC_CLOCKEVENTS
> diff --git a/drivers/clocksource/Makefile b/drivers/clocksource/Makefile
> index fd9d6df..cf87f40 100644
> --- a/drivers/clocksource/Makefile
> +++ b/drivers/clocksource/Makefile
> @@ -5,6 +5,7 @@ obj-$(CONFIG_ATMEL_TCB_CLKSRC)	+= tcb_clksrc.o
>  obj-$(CONFIG_X86_PM_TIMER)	+= acpi_pm.o
>  obj-$(CONFIG_SCx200HR_TIMER)	+= scx200_hrt.o
>  obj-$(CONFIG_CS5535_CLOCK_EVENT_SRC)	+= cs5535-clockevt.o
> +obj-$(CONFIG_CLKSRC_JCORE_PIT)		+= jcore-pit.o
>  obj-$(CONFIG_SH_TIMER_CMT)	+= sh_cmt.o
>  obj-$(CONFIG_SH_TIMER_MTU2)	+= sh_mtu2.o
>  obj-$(CONFIG_SH_TIMER_TMU)	+= sh_tmu.o
> diff --git a/drivers/clocksource/jcore-pit.c b/drivers/clocksource/jcore-pit.c
> new file mode 100644
> index 0000000..4c512d7
> --- /dev/null
> +++ b/drivers/clocksource/jcore-pit.c
> @@ -0,0 +1,240 @@
> +/*
> + * J-Core SoC PIT/clocksource driver
> + *
> + * Copyright (C) 2015-2016 Smart Energy Instruments, Inc.
> + *
> + * This file is subject to the terms and conditions of the GNU General Public
> + * License.  See the file "COPYING" in the main directory of this archive
> + * for more details.
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/slab.h>
> +#include <linux/interrupt.h>
> +#include <linux/clockchips.h>
> +#include <linux/clocksource.h>
> +#include <linux/sched_clock.h>
> +#include <linux/cpu.h>
> +#include <linux/cpuhotplug.h>
> +#include <linux/of_address.h>
> +#include <linux/of_irq.h>
> +
> +#define PIT_IRQ_SHIFT		12
> +#define PIT_PRIO_SHIFT		20
> +#define PIT_ENABLE_SHIFT	26
> +#define PIT_IRQ_MASK		0x3f
> +#define PIT_PRIO_MASK		0xf
> +
> +#define REG_PITEN		0x00
> +#define REG_THROT		0x10
> +#define REG_COUNT		0x14
> +#define REG_BUSPD		0x18
> +#define REG_SECHI		0x20
> +#define REG_SECLO		0x24
> +#define REG_NSEC		0x28
> +
> +struct jcore_pit {
> +	struct clock_event_device	ced;
> +	__iomem void			*base;
> +	unsigned long			periodic_delta;
> +	unsigned			cpu;
> +	u32				enable_val;
> +};
> +
> +static __iomem void		*jcore_pit_base;
> +struct jcore_pit __percpu	*jcore_pit_percpu;
> +
> +static notrace u64 jcore_sched_clock_read(void)
> +{
> +	u32 seclo, nsec, seclo0;
> +	__iomem void *base = jcore_pit_base;
> +
> +	seclo = readl(base + REG_SECLO);
> +	do {
> +		seclo0 = seclo;
> +		nsec  = readl(base + REG_NSEC);
> +		seclo = readl(base + REG_SECLO);
> +	} while (seclo0 != seclo);
> +
> +	return seclo * NSEC_PER_SEC + nsec;
> +}
> +
> +static cycle_t jcore_clocksource_read(struct clocksource *cs)
> +{
> +	return jcore_sched_clock_read();
> +}
> +
> +static int jcore_pit_disable(struct jcore_pit *pit)
> +{
> +	writel(0, pit->base + REG_PITEN);
> +	return 0;
> +}
> +
> +static int jcore_pit_set(unsigned long delta, struct jcore_pit *pit)
> +{
> +	jcore_pit_disable(pit);
> +	writel(delta, pit->base + REG_THROT);
> +	writel(pit->enable_val, pit->base + REG_PITEN);
> +	return 0;
> +}
> +
> +static int jcore_pit_set_state_shutdown(struct clock_event_device *ced)
> +{
> +	struct jcore_pit *pit = container_of(ced, struct jcore_pit, ced);
> +
> +	return jcore_pit_disable(pit);
> +}
> +
> +static int jcore_pit_set_state_oneshot(struct clock_event_device *ced)
> +{
> +	struct jcore_pit *pit = container_of(ced, struct jcore_pit, ced);
> +
> +	return jcore_pit_disable(pit);
> +}
> +
> +static int jcore_pit_set_state_periodic(struct clock_event_device *ced)
> +{
> +	struct jcore_pit *pit = container_of(ced, struct jcore_pit, ced);
> +
> +	return jcore_pit_set(pit->periodic_delta, pit);
> +}
> +
> +static int jcore_pit_set_next_event(unsigned long delta,
> +				    struct clock_event_device *ced)
> +{
> +	struct jcore_pit *pit = container_of(ced, struct jcore_pit, ced);
> +
> +	return jcore_pit_set(delta, pit);
> +}
> +
> +static int jcore_pit_local_init(unsigned cpu)
> +{
> +	struct jcore_pit *pit = this_cpu_ptr(jcore_pit_percpu);
> +	unsigned buspd, freq, min_delta;
> +
> +	pr_info("Local J-Core PIT init on cpu %u\n", pit->cpu);
> +
> +	buspd = readl(pit->base + REG_BUSPD);
> +	freq = DIV_ROUND_CLOSEST(NSEC_PER_SEC, buspd);
> +	pit->periodic_delta = DIV_ROUND_CLOSEST(NSEC_PER_SEC, HZ * buspd);
> +
> +	/*
> +	 * This is a workaround. When the timer system schedules oneshot
> +	 * events so soon that the interrupt occurs before the softirq
> +	 * part of the timer handler runs, a feedback loop ensues and
> +	 * results in long stalls that are broken up only by other
> +	 * interrupt activity.
> +	 */
> +	min_delta = DIV_ROUND_CLOSEST(5000000, buspd);
> +
> +	clockevents_config_and_register(&pit->ced, freq, min_delta, ULONG_MAX);
> +
> +	return 0;
> +}
> +
> +static irqreturn_t jcore_timer_interrupt(int irq, void *dev_id)
> +{
> +	struct jcore_pit *pit = this_cpu_ptr(dev_id);
> +
> +	if (clockevent_state_oneshot(&pit->ced))
> +		jcore_pit_disable(pit);
> +
> +	pit->ced.event_handler(&pit->ced);
> +
> +	return IRQ_HANDLED;
> +}
> +
> +static int __init jcore_pit_init(struct device_node *node)
> +{
> +	int err;
> +	unsigned pit_irq, cpu;
> +	unsigned long hwirq;
> +	u32 irqprio, enable_val;
> +
> +	jcore_pit_base = of_iomap(node, 0);
> +	if (!jcore_pit_base) {
> +		pr_err("Error: Cannot map base address for J-Core PIT\n");
> +		return -ENXIO;
> +	}
> +
> +	pit_irq = irq_of_parse_and_map(node, 0);
> +	if (!pit_irq) {
> +		pr_err("Error: J-Core PIT has no IRQ\n");
> +		return -ENXIO;
> +	}
> +
> +	pr_info("Initializing J-Core PIT at %p IRQ %d\n",
> +		jcore_pit_base, pit_irq);
> +
> +	err = clocksource_mmio_init(jcore_pit_base, "jcore_pit_cs",
> +				    NSEC_PER_SEC, 400, 32,
> +				    jcore_clocksource_read);
> +	if (err) {
> +		pr_err("Error registering clocksource device: %d\n", err);
> +		return err;
> +	}
> +
> +	sched_clock_register(jcore_sched_clock_read, 32, NSEC_PER_SEC);
> +
> +	jcore_pit_percpu = alloc_percpu(struct jcore_pit);
> +	if (!jcore_pit_percpu) {
> +		pr_err("Failed to allocate memory for clock event device\n");
> +		return -ENOMEM;
> +	}
> +
> +	err = request_irq(pit_irq, jcore_timer_interrupt,
> +			  IRQF_TIMER | IRQF_PERCPU,
> +			  "jcore_pit", jcore_pit_percpu);
> +	if (err) {
> +		pr_err("pit irq request failed: %d\n", err);
> +		free_percpu(jcore_pit_percpu);
> +		return err;
> +	}
> +
> +	/*
> +	 * The J-Core PIT is not hard-wired to a particular IRQ, but
> +	 * integrated with the interrupt controller such that the IRQ it
> +	 * generates is programmable. The programming interface has a
> +	 * legacy field which was an interrupt priority for AIC1, but
> +	 * which is OR'd onto bits 2-5 of the generated IRQ number when
> +	 * used with J-Core AIC2, so set it to match these bits.
> +	 */
> +	hwirq = irq_get_irq_data(pit_irq)->hwirq;
> +	irqprio = (hwirq >> 2) & PIT_PRIO_MASK;
> +	enable_val = (1U << PIT_ENABLE_SHIFT)
> +		   | (hwirq << PIT_IRQ_SHIFT)
> +		   | (irqprio << PIT_PRIO_SHIFT);
> +
> +	for_each_present_cpu(cpu) {
> +		struct jcore_pit *pit = per_cpu_ptr(jcore_pit_percpu, cpu);
> +
> +		pit->base = of_iomap(node, cpu);
> +		if (!pit->base) {
> +			pr_err("Unable to map PIT for cpu %u\n", cpu);
> +			continue;
> +		}
> +
> +		pit->ced.name = "jcore_pit";
> +		pit->ced.features = CLOCK_EVT_FEAT_PERIODIC
> +				  | CLOCK_EVT_FEAT_ONESHOT
> +				  | CLOCK_EVT_FEAT_PERCPU;
> +		pit->ced.cpumask = cpumask_of(cpu);
> +		pit->ced.rating = 400;
> +		pit->ced.irq = pit_irq;
> +		pit->ced.set_state_shutdown = jcore_pit_set_state_shutdown;
> +		pit->ced.set_state_periodic = jcore_pit_set_state_periodic;
> +		pit->ced.set_state_oneshot = jcore_pit_set_state_oneshot;
> +		pit->ced.set_next_event = jcore_pit_set_next_event;
> +
> +		pit->cpu = cpu;
> +		pit->enable_val = enable_val;
> +	}
> +
> +	cpuhp_setup_state(CPUHP_AP_JCORE_TIMER_STARTING,
> +			  "AP_JCORE_TIMER_STARTING",
> +			  jcore_pit_local_init, NULL);
> +
> +	return 0;
> +}
> +
> +CLOCKSOURCE_OF_DECLARE(jcore_pit, "jcore,pit", jcore_pit_init);
> diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
> index 34bd805..e2e6c8c 100644
> --- a/include/linux/cpuhotplug.h
> +++ b/include/linux/cpuhotplug.h
> @@ -52,6 +52,7 @@ enum cpuhp_state {
>  	CPUHP_AP_ARM_ARCH_TIMER_STARTING,
>  	CPUHP_AP_ARM_GLOBAL_TIMER_STARTING,
>  	CPUHP_AP_DUMMY_TIMER_STARTING,
> +	CPUHP_AP_JCORE_TIMER_STARTING,
>  	CPUHP_AP_EXYNOS4_MCT_TIMER_STARTING,
>  	CPUHP_AP_ARM_TWD_STARTING,
>  	CPUHP_AP_METAG_TIMER_STARTING,
> -- 
> 2.10.0

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