clocksource: ep93xx: Add driver for Cirrus Logic EP93xx

Rewrite EP93xx timer driver located in arch/arm/mach-ep93xx/timer-ep93xx.c
trying to do everything the device tree way:

- Make every IO-access relative to a base address and dynamic
  so we can do a dynamic ioremap and get going.
- Find register range and interrupt from the device tree.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Tested-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>
Signed-off-by: Nikita Shubin <nikita.shubin@maquefel.me>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20230915-ep93xx-v4-12-a1d779dcec10@maquefel.me

drivers/clocksource/Kconfig

@@ -732,4 +732,15 @@ config GOLDFISH_TIMER
 	help
 	  Support for the timer/counter of goldfish-rtc
 
+config EP93XX_TIMER
+	bool "Cirrus Logic ep93xx timer driver" if COMPILE_TEST
+	depends on ARCH_EP93XX
+	depends on GENERIC_CLOCKEVENTS
+	depends on HAS_IOMEM
+	select CLKSRC_MMIO
+	select TIMER_OF
+	help
+	  Enables support for the Cirrus Logic timer block
+	  EP93XX.
+
 endmenu

drivers/clocksource/Makefile

@@ -89,3 +89,4 @@ obj-$(CONFIG_MSC313E_TIMER)		+= timer-msc313e.o
 obj-$(CONFIG_GOLDFISH_TIMER)		+= timer-goldfish.o
 obj-$(CONFIG_GXP_TIMER)			+= timer-gxp.o
 obj-$(CONFIG_CLKSRC_LOONGSON1_PWM)	+= timer-loongson1-pwm.o
+obj-$(CONFIG_EP93XX_TIMER)		+= timer-ep93xx.o

drivers/clocksource/timer-ep93xx.c

@@ -0,0 +1,190 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Cirrus Logic EP93xx timer driver.
+ * Copyright (C) 2021 Nikita Shubin <nikita.shubin@maquefel.me>
+ *
+ * Based on a rewrite of arch/arm/mach-ep93xx/timer.c:
+ */
+
+#include <linux/clockchips.h>
+#include <linux/clocksource.h>
+#include <linux/init.h>
+#include <linux/interrupt.h>
+#include <linux/io.h>
+#include <linux/io-64-nonatomic-lo-hi.h>
+#include <linux/irq.h>
+#include <linux/kernel.h>
+#include <linux/of_address.h>
+#include <linux/of_irq.h>
+#include <linux/sched_clock.h>
+
+#include <asm/mach/time.h>
+
+/*************************************************************************
+ * Timer handling for EP93xx
+ *************************************************************************
+ * The ep93xx has four internal timers.  Timers 1, 2 (both 16 bit) and
+ * 3 (32 bit) count down at 508 kHz, are self-reloading, and can generate
+ * an interrupt on underflow.  Timer 4 (40 bit) counts down at 983.04 kHz,
+ * is free-running, and can't generate interrupts.
+ *
+ * The 508 kHz timers are ideal for use for the timer interrupt, as the
+ * most common values of HZ divide 508 kHz nicely.  We pick the 32 bit
+ * timer (timer 3) to get as long sleep intervals as possible when using
+ * CONFIG_NO_HZ.
+ *
+ * The higher clock rate of timer 4 makes it a better choice than the
+ * other timers for use as clock source and for sched_clock(), providing
+ * a stable 40 bit time base.
+ *************************************************************************
+ */
+
+#define EP93XX_TIMER1_LOAD		0x00
+#define EP93XX_TIMER1_VALUE		0x04
+#define EP93XX_TIMER1_CONTROL		0x08
+#define EP93XX_TIMER123_CONTROL_ENABLE	BIT(7)
+#define EP93XX_TIMER123_CONTROL_MODE	BIT(6)
+#define EP93XX_TIMER123_CONTROL_CLKSEL	BIT(3)
+#define EP93XX_TIMER1_CLEAR		0x0c
+#define EP93XX_TIMER2_LOAD		0x20
+#define EP93XX_TIMER2_VALUE		0x24
+#define EP93XX_TIMER2_CONTROL		0x28
+#define EP93XX_TIMER2_CLEAR		0x2c
+/*
+ * This read-only register contains the low word of the time stamp debug timer
+ * ( Timer4). When this register is read, the high byte of the Timer4 counter is
+ * saved in the Timer4ValueHigh register.
+ */
+#define EP93XX_TIMER4_VALUE_LOW		0x60
+#define EP93XX_TIMER4_VALUE_HIGH	0x64
+#define EP93XX_TIMER4_VALUE_HIGH_ENABLE	BIT(8)
+#define EP93XX_TIMER3_LOAD		0x80
+#define EP93XX_TIMER3_VALUE		0x84
+#define EP93XX_TIMER3_CONTROL		0x88
+#define EP93XX_TIMER3_CLEAR		0x8c
+
+#define EP93XX_TIMER123_RATE		508469
+#define EP93XX_TIMER4_RATE		983040
+
+struct ep93xx_tcu {
+	void __iomem *base;
+};
+
+static struct ep93xx_tcu *ep93xx_tcu;
+
+static u64 ep93xx_clocksource_read(struct clocksource *c)
+{
+	struct ep93xx_tcu *tcu = ep93xx_tcu;
+
+	return lo_hi_readq(tcu->base + EP93XX_TIMER4_VALUE_LOW) & GENMASK_ULL(39, 0);
+}
+
+static u64 notrace ep93xx_read_sched_clock(void)
+{
+	return ep93xx_clocksource_read(NULL);
+}
+
+static int ep93xx_clkevt_set_next_event(unsigned long next,
+					struct clock_event_device *evt)
+{
+	struct ep93xx_tcu *tcu = ep93xx_tcu;
+	/* Default mode: periodic, off, 508 kHz */
+	u32 tmode = EP93XX_TIMER123_CONTROL_MODE |
+	EP93XX_TIMER123_CONTROL_CLKSEL;
+
+	/* Clear timer */
+	writel(tmode, tcu->base + EP93XX_TIMER3_CONTROL);
+
+	/* Set next event */
+	writel(next, tcu->base + EP93XX_TIMER3_LOAD);
+	writel(tmode | EP93XX_TIMER123_CONTROL_ENABLE,
+	       tcu->base + EP93XX_TIMER3_CONTROL);
+	return 0;
+}
+
+static int ep93xx_clkevt_shutdown(struct clock_event_device *evt)
+{
+	struct ep93xx_tcu *tcu = ep93xx_tcu;
+	/* Disable timer */
+	writel(0, tcu->base + EP93XX_TIMER3_CONTROL);
+
+	return 0;
+}
+
+static struct clock_event_device ep93xx_clockevent = {
+	.name			= "timer1",
+	.features		= CLOCK_EVT_FEAT_ONESHOT,
+	.set_state_shutdown	= ep93xx_clkevt_shutdown,
+	.set_state_oneshot	= ep93xx_clkevt_shutdown,
+	.tick_resume		= ep93xx_clkevt_shutdown,
+	.set_next_event		= ep93xx_clkevt_set_next_event,
+	.rating			= 300,
+};
+
+static irqreturn_t ep93xx_timer_interrupt(int irq, void *dev_id)
+{
+	struct ep93xx_tcu *tcu = ep93xx_tcu;
+	struct clock_event_device *evt = dev_id;
+
+	/* Writing any value clears the timer interrupt */
+	writel(1, tcu->base + EP93XX_TIMER3_CLEAR);
+
+	evt->event_handler(evt);
+
+	return IRQ_HANDLED;
+}
+
+static int __init ep93xx_timer_of_init(struct device_node *np)
+{
+	int irq;
+	unsigned long flags = IRQF_TIMER | IRQF_IRQPOLL;
+	struct ep93xx_tcu *tcu;
+	int ret;
+
+	tcu = kzalloc(sizeof(*tcu), GFP_KERNEL);
+	if (!tcu)
+		return -ENOMEM;
+
+	tcu->base = of_iomap(np, 0);
+	if (!tcu->base) {
+		pr_err("Can't remap registers\n");
+		ret = -ENXIO;
+		goto out_free;
+	}
+
+	ep93xx_tcu = tcu;
+
+	irq = irq_of_parse_and_map(np, 0);
+	if (irq == 0)
+		irq = -EINVAL;
+	if (irq < 0) {
+		pr_err("EP93XX Timer Can't parse IRQ %d", irq);
+		goto out_free;
+	}
+
+	/* Enable and register clocksource and sched_clock on timer 4 */
+	writel(EP93XX_TIMER4_VALUE_HIGH_ENABLE,
+	       tcu->base + EP93XX_TIMER4_VALUE_HIGH);
+	clocksource_mmio_init(NULL, "timer4",
+				EP93XX_TIMER4_RATE, 200, 40,
+				ep93xx_clocksource_read);
+	sched_clock_register(ep93xx_read_sched_clock, 40,
+			     EP93XX_TIMER4_RATE);
+
+	/* Set up clockevent on timer 3 */
+	if (request_irq(irq, ep93xx_timer_interrupt, flags, "ep93xx timer",
+		&ep93xx_clockevent))
+		pr_err("Failed to request irq %d (ep93xx timer)\n", irq);
+
+	clockevents_config_and_register(&ep93xx_clockevent,
+				EP93XX_TIMER123_RATE,
+				1,
+				UINT_MAX);
+
+	return 0;
+
+out_free:
+	kfree(tcu);
+	return ret;
+}
+TIMER_OF_DECLARE(ep93xx_timer, "cirrus,ep9301-timer", ep93xx_timer_of_init);