[PATCH v4 2/2] clocksource: add J-Core timer/clocksource driver

[Rich Felker]

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. The code has been
tested and works on SMP, but will not be usable without additional
J-Core SMP-support patches and appropriate hardware capable of running
SMP.

A nanosecond-resolution clocksource is provided using the J-Core "RTC"
registers, which give a 64-bit seconds count and 32-bit nanoseconds.
The driver converts these to a 64-bit nanoseconds count.

Signed-off-by: Rich Felker <dalias@xxxxxxxx>
---
 drivers/clocksource/Kconfig     |   8 ++
 drivers/clocksource/Makefile    |   1 +
 drivers/clocksource/jcore-pit.c | 277 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 286 insertions(+)
 create mode 100644 drivers/clocksource/jcore-pit.c

diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
index 47352d2..b6d4d43 100644
--- a/drivers/clocksource/Kconfig
+++ b/drivers/clocksource/Kconfig
@@ -313,6 +313,14 @@ config SYS_SUPPORTS_SH_TMU
 config SYS_SUPPORTS_EM_STI
         bool
 
+config CLKSRC_JCORE_PIT
+	bool "J-Core PIT timer driver"
+	depends on GENERIC_CLOCKEVENTS
+	depends on HAS_IOMEM
+	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 473974f..b41a834 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..373b9f9
--- /dev/null
+++ b/drivers/clocksource/jcore-pit.c
@@ -0,0 +1,277 @@
+/*
+ * 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/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_clocksource {
+	struct clocksource cs;
+	__iomem void *base;
+};
+
+struct jcore_pit {
+	struct clock_event_device ced;
+	__iomem void *base;
+	unsigned long periodic_delta;
+	unsigned cpu;
+	u32 enable_val;
+};
+
+struct jcore_pit_nb {
+	struct notifier_block nb;
+	struct jcore_pit __percpu *pit_percpu;
+};
+
+static struct clocksource *jcore_cs;
+
+static cycle_t jcore_clocksource_read(struct clocksource *cs)
+{
+	__iomem void *base =
+		container_of(cs, struct jcore_clocksource, cs)->base;
+	u32 sechi, seclo, nsec, sechi0, seclo0;
+
+	sechi = __raw_readl(base + REG_SECHI);
+	seclo = __raw_readl(base + REG_SECLO);
+	do {
+		sechi0 = sechi;
+		seclo0 = seclo;
+		nsec  = __raw_readl(base + REG_NSEC);
+		sechi = __raw_readl(base + REG_SECHI);
+		seclo = __raw_readl(base + REG_SECLO);
+	} while (sechi0 != sechi || seclo0 != seclo);
+
+	return ((u64)sechi << 32 | seclo) * NSEC_PER_SEC + nsec;
+}
+
+static notrace u64 jcore_sched_clock_read(void)
+{
+	return jcore_clocksource_read(jcore_cs);
+}
+
+static int jcore_pit_disable(struct jcore_pit *pit)
+{
+	__raw_writel(0, pit->base + REG_PITEN);
+	return 0;
+}
+
+static int jcore_pit_set(unsigned long delta, struct jcore_pit *pit)
+{
+	jcore_pit_disable(pit);
+	__raw_writel(delta, pit->base + REG_THROT);
+	__raw_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(struct jcore_pit *pit)
+{
+	unsigned buspd, freq;
+
+	pr_info("Local J-Core PIT init on cpu %u\n", pit->cpu);
+
+	buspd = __raw_readl(pit->base + REG_BUSPD);
+	freq = DIV_ROUND_CLOSEST(NSEC_PER_SEC, buspd);
+	pit->periodic_delta = DIV_ROUND_CLOSEST(NSEC_PER_SEC, HZ*buspd);
+
+	clockevents_config_and_register(&pit->ced, freq, 1, ULONG_MAX);
+
+	return 0;
+}
+
+static int jcore_pit_cpu_notify(struct notifier_block *self,
+			unsigned long action, void *hcpu)
+{
+	struct jcore_pit_nb *nb = container_of(self, struct jcore_pit_nb, nb);
+	switch (action & ~CPU_TASKS_FROZEN) {
+	case CPU_STARTING:
+		jcore_pit_local_init(this_cpu_ptr(nb->pit_percpu));
+		break;
+	}
+	return NOTIFY_OK;
+}
+
+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 void __init jcore_pit_init(struct device_node *node)
+{
+	int err;
+	__iomem void *pit_base;
+	unsigned pit_irq;
+	unsigned cpu;
+	struct jcore_pit_nb *nb = 0;
+	struct jcore_clocksource *cs = 0;
+	struct jcore_pit __percpu *pit_percpu = 0;
+	unsigned long hwirq;
+	u32 irqprio, enable_val;
+
+	pit_base = of_iomap(node, 0);
+	if (!pit_base) {
+		pr_err("Error: Cannot map base address for J-Core PIT\n");
+		goto out;
+	}
+
+	pit_irq = irq_of_parse_and_map(node, 0);
+	if (!pit_irq) {
+		pr_err("Error: J-Core PIT has no IRQ\n");
+		goto out;
+	}
+
+	pr_info("Initializing J-Core PIT at %p IRQ %d\n", pit_base, pit_irq);
+
+	cs = kzalloc(sizeof *cs, GFP_KERNEL);
+	if (!cs) {
+		pr_err("Failed to allocate memory for clocksource\n");
+		goto out;
+	}
+	jcore_cs = &cs->cs;
+
+	cs->base = pit_base;
+	cs->cs.name = "jcore_pit_cs";
+	cs->cs.rating = 400;
+	cs->cs.read = jcore_clocksource_read;
+	cs->cs.mult = 1;
+	cs->cs.shift = 0;
+	cs->cs.mask = CLOCKSOURCE_MASK(64);
+	cs->cs.flags = CLOCK_SOURCE_IS_CONTINUOUS;
+
+	err = clocksource_register_hz(&cs->cs, NSEC_PER_SEC);
+	if (err) {
+		pr_err("Error registering clocksource device: %d\n", err);
+		goto out;
+	}
+
+	sched_clock_register(jcore_sched_clock_read, 64, NSEC_PER_SEC);
+
+	pit_percpu = alloc_percpu(struct jcore_pit);
+	if (!pit_percpu) {
+		pr_err("Failed to allocate memory for clock event device\n");
+		goto out;
+	}
+
+	nb = kzalloc(sizeof *nb, GFP_KERNEL);
+	if (!nb) {
+		pr_err("Failed to allocate memory for J-Core PIT notifier\n");
+		goto out;
+	}
+
+	nb->pit_percpu = pit_percpu;
+	nb->nb.notifier_call = jcore_pit_cpu_notify;
+	err = register_cpu_notifier(&nb->nb);
+	if (err) {
+		pr_err("Error registering J-Core PIT notifier: %d\n", err);
+		goto out;
+	}
+
+	err = request_irq(pit_irq, jcore_timer_interrupt,
+		IRQF_TIMER | IRQF_PERCPU, "jcore_pit", pit_percpu);
+	if (err) {
+		pr_err("pit irq request failed: %d\n", err);
+		goto out;
+	}
+
+	/* 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_possible_cpu(cpu) {
+		struct jcore_pit *pit = per_cpu_ptr(pit_percpu, cpu);
+
+		pit->base = of_iomap(node, cpu);
+		if (!pit->base)
+			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;
+	}
+
+	jcore_pit_local_init(this_cpu_ptr(pit_percpu));
+
+	return;
+
+out:
+	pr_err("Could not initialize J-Core PIT driver\n");
+}
+
+CLOCKSOURCE_OF_DECLARE(jcore_pit, "jcore,pit", jcore_pit_init);
-- 
2.8.1