realtek: resurrect timer driver

Now that we provide a clock driver for the Reltek SOCs the CPU frequency might
change on demand. This has direct visible effects during operation

- the CEVT 4K timer is no longer a stable clocksource
- after CPU frequencies changes time calculation works wrong
- sched_clock falls back to kernel default interval (100 Hz)
- timestamps in dmesg have only 2 digits left

[    0.000000] sched_clock: 32 bits at 100 Hz, resolution 10000000ns, wraps ...
[    0.060000] pid_max: default: 32768 minimum: 301
[    0.070000] Mount-cache hash table entries: 1024 (order: 0, 4096 bytes, linear)
[    0.070000] Mountpoint-cache hash table entries: 1024 (order: 0, 4096 bytes, linear)
[    0.080000] dyndbg: Ignore empty _ddebug table in a CONFIG_DYNAMIC_DEBUG_CORE build
[    0.090000] clocksource: jiffies: mask: 0xffffffff max_cycles: 0xffffffff, ...

Looking around where we can start the CEVT timer for RTL930X is a good basis.
Initially it was developed as a clocksource driver for the broken timer in that
specific SOC series. Afterwards it was shifted around to the CEVT location,
got SMP enablement and lost its clocksource feature. So we at least have
something to copy from. As the timers on these devices are well understood
the implementation follows this way:

- leave the RTL930X implementation as is
- provide a new driver for RTL83XX devices only
- swap RTL930X driver at a later time

Like the clock driver this patch contains a self contained module that is SOC
independet and already provides full support for the RTL838X, RTL839X and
RTL930X devices. Some of the new (or reestablished) features are:

- simplified initialization routines
- SMP setup with CPU hotplug framework
- derived from LXB clock speed
- supplied clocksource
- dedicated register functions for better readability
- documentation about some caveats

Signed-off-by: Markus Stockhausen <markus.stockhausen@gmx.de>
[remove unused header includes, remove old CONFIG_MIPS dependency, add
REALTEK_ prefix to driver symbol]
Signed-off-by: Sander Vanheule <sander@svanheule.net>

target/linux/realtek/files-5.10/drivers/clocksource/timer-rtl-otto.c

@@ -0,0 +1,298 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include <linux/clk.h>
+#include <linux/clockchips.h>
+#include <linux/cpu.h>
+#include <linux/cpuhotplug.h>
+#include <linux/interrupt.h>
+#include <linux/sched_clock.h>
+
+#include "timer-of.h"
+
+#define RTTM_DATA		0x0
+#define RTTM_CNT		0x4
+#define RTTM_CTRL		0x8
+#define RTTM_INT		0xc
+
+#define RTTM_CTRL_ENABLE	BIT(28)
+#define RTTM_INT_PENDING	BIT(16)
+#define RTTM_INT_ENABLE		BIT(20)
+
+/*
+ * The Otto platform provides multiple 28 bit timers/counters with the following
+ * operating logic. If enabled the timer counts up. Per timer one can set a
+ * maximum counter value as an end marker. If end marker is reached the timer
+ * fires an interrupt. If the timer "overflows" by reaching the end marker or
+ * by adding 1 to 0x0fffffff the counter is reset to 0. When this happens and
+ * the timer is in operating mode COUNTER it stops. In mode TIMER it will
+ * continue to count up.
+ */
+
+#define RTTM_CTRL_COUNTER	0
+#define RTTM_CTRL_TIMER		BIT(24)
+
+#define RTTM_BIT_COUNT		28
+#define RTTM_MIN_DELTA		8
+#define RTTM_MAX_DELTA		CLOCKSOURCE_MASK(28)
+
+/*
+ * Timers are derived from the LXB clock frequency. Usually this is a fixed
+ * multiple of the 25 MHz oscillator. The 930X SOC is an exception from that.
+ * Its LXB clock has only dividers and uses the switch PLL of 2.45 GHz as its
+ * base. The only meaningful frequencies we can achieve from that are 175.000
+ * MHz and 153.125 MHz. The greatest common divisor of all explained possible
+ * speeds is 3125000. Pin the timers to this 3.125 MHz reference frequency.
+ */
+
+#define RTTM_TICKS_PER_SEC	3125000
+
+struct rttm_cs {
+	struct timer_of		to;
+	struct clocksource	cs;
+};
+
+/*
+ * Simple internal register functions
+ */
+
+static inline void rttm_set_counter(void __iomem *base, unsigned int counter)
+{
+	iowrite32(counter, base + RTTM_CNT);
+}
+
+static inline unsigned int rttm_get_counter(void __iomem *base)
+{
+	return ioread32(base + RTTM_CNT);
+}
+
+static inline void rttm_set_period(void __iomem *base, unsigned int period)
+{
+	iowrite32(period, base + RTTM_DATA);
+}
+
+static inline void rttm_disable_timer(void __iomem *base)
+{
+	iowrite32(0, base + RTTM_CTRL);
+}
+
+static inline void rttm_enable_timer(void __iomem *base, u32 mode, u32 divisor)
+{
+	iowrite32(RTTM_CTRL_ENABLE | mode | divisor, base + RTTM_CTRL);
+}
+
+static inline void rttm_ack_irq(void __iomem *base)
+{
+	iowrite32(ioread32(base + RTTM_INT) | RTTM_INT_PENDING, base + RTTM_INT);
+}
+
+static inline void rttm_enable_irq(void __iomem *base)
+{
+	iowrite32(RTTM_INT_ENABLE, base + RTTM_INT);
+}
+
+static inline void rttm_disable_irq(void __iomem *base)
+{
+	iowrite32(0, base + RTTM_INT);
+}
+
+/*
+ * Aggregated control functions for kernel clock framework
+ */
+
+#define RTTM_DEBUG(base)					\
+	pr_debug("------------- %s %d %08x\n", __func__,	\
+	smp_processor_id(), (u32)base)
+
+static irqreturn_t rttm_timer_interrupt(int irq, void *dev_id)
+{
+	struct clock_event_device *clkevt = dev_id;
+	struct timer_of *to = to_timer_of(clkevt);
+
+	rttm_ack_irq(to->of_base.base);
+	RTTM_DEBUG(to->of_base.base);
+	clkevt->event_handler(clkevt);
+
+	return IRQ_HANDLED;
+}
+
+static void rttm_stop_timer(void __iomem *base)
+{
+	rttm_disable_timer(base);
+	rttm_ack_irq(base);
+}
+
+static void rttm_start_timer(struct timer_of *to, u32 mode)
+{
+	rttm_set_counter(to->of_base.base, 0);
+	rttm_enable_timer(to->of_base.base, mode, to->of_clk.rate / RTTM_TICKS_PER_SEC);
+}
+
+static int rttm_next_event(unsigned long delta, struct clock_event_device *clkevt)
+{
+	struct timer_of *to = to_timer_of(clkevt);
+
+	RTTM_DEBUG(to->of_base.base);
+	rttm_stop_timer(to->of_base.base);
+	rttm_set_period(to->of_base.base, delta);
+	rttm_start_timer(to, RTTM_CTRL_COUNTER);
+
+	return 0;
+}
+
+static int rttm_state_oneshot(struct clock_event_device *clkevt)
+{
+	struct timer_of *to = to_timer_of(clkevt);
+
+	RTTM_DEBUG(to->of_base.base);
+	rttm_stop_timer(to->of_base.base);
+	rttm_set_period(to->of_base.base, RTTM_TICKS_PER_SEC / HZ);
+	rttm_start_timer(to, RTTM_CTRL_COUNTER);
+
+	return 0;
+}
+
+static int rttm_state_periodic(struct clock_event_device *clkevt)
+{
+	struct timer_of *to = to_timer_of(clkevt);
+
+	RTTM_DEBUG(to->of_base.base);
+	rttm_stop_timer(to->of_base.base);
+	rttm_set_period(to->of_base.base, RTTM_TICKS_PER_SEC / HZ);
+	rttm_start_timer(to, RTTM_CTRL_TIMER);
+
+	return 0;
+}
+
+static int rttm_state_shutdown(struct clock_event_device *clkevt)
+{
+	struct timer_of *to = to_timer_of(clkevt);
+
+	RTTM_DEBUG(to->of_base.base);
+	rttm_stop_timer(to->of_base.base);
+
+	return 0;
+}
+
+static void rttm_setup_timer(void __iomem *base)
+{
+	RTTM_DEBUG(base);
+	rttm_stop_timer(base);
+	rttm_set_period(base, 0);
+}
+
+static u64 rttm_read_clocksource(struct clocksource *cs)
+{
+	struct rttm_cs *rcs = container_of(cs, struct rttm_cs, cs);
+
+	return (u64)rttm_get_counter(rcs->to.of_base.base);
+}
+
+/*
+ * Module initialization part.
+ */
+
+static DEFINE_PER_CPU(struct timer_of, rttm_to) = {
+	.flags				= TIMER_OF_BASE | TIMER_OF_CLOCK | TIMER_OF_IRQ,
+	.of_irq = {
+		.flags			= IRQF_PERCPU | IRQF_TIMER,
+		.handler		= rttm_timer_interrupt,
+	},
+	.clkevt = {
+		.rating			= 400,
+		.features		= CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT,
+		.set_state_periodic	= rttm_state_periodic,
+		.set_state_shutdown	= rttm_state_shutdown,
+		.set_state_oneshot	= rttm_state_oneshot,
+		.set_next_event		= rttm_next_event
+	},
+};
+
+static int rttm_enable_clocksource(struct clocksource *cs)
+{
+	struct rttm_cs *rcs = container_of(cs, struct rttm_cs, cs);
+
+	rttm_disable_irq(rcs->to.of_base.base);
+	rttm_setup_timer(rcs->to.of_base.base);
+	rttm_enable_timer(rcs->to.of_base.base, RTTM_CTRL_TIMER,
+			  rcs->to.of_clk.rate / RTTM_TICKS_PER_SEC);
+
+	return 0;
+}
+
+struct rttm_cs rttm_cs = {
+	.to = {
+		.flags	= TIMER_OF_BASE | TIMER_OF_CLOCK,
+	},
+	.cs = {
+		.name	= "realtek_otto_timer",
+		.rating	= 400,
+		.mask	= CLOCKSOURCE_MASK(RTTM_BIT_COUNT),
+		.read	= rttm_read_clocksource,
+		.enable	= rttm_enable_clocksource
+	}
+};
+
+static u64 notrace rttm_read_clock(void)
+{
+	return (u64)rttm_get_counter(rttm_cs.to.of_base.base);
+}
+
+static int rttm_cpu_starting(unsigned int cpu)
+{
+	struct timer_of *to = per_cpu_ptr(&rttm_to, cpu);
+
+	RTTM_DEBUG(to->of_base.base);
+	to->clkevt.cpumask = cpumask_of(cpu);
+	irq_set_affinity(to->of_irq.irq, to->clkevt.cpumask);
+	clockevents_config_and_register(&to->clkevt, RTTM_TICKS_PER_SEC,
+					RTTM_MIN_DELTA, RTTM_MAX_DELTA);
+	rttm_enable_irq(to->of_base.base);
+
+	return 0;
+}
+
+static int __init rttm_probe(struct device_node *np)
+{
+	int cpu, cpu_rollback;
+	struct timer_of *to;
+	int clkidx = num_possible_cpus();
+/*
+ * Use the first n timers as per CPU clock event generators
+ */
+	for_each_possible_cpu(cpu) {
+		to = per_cpu_ptr(&rttm_to, cpu);
+		to->of_irq.index = to->of_base.index = cpu;
+		if (timer_of_init(np, to)) {
+			pr_err("%s: setup of timer %d failed\n", __func__, cpu);
+			goto rollback;
+		}
+		rttm_setup_timer(to->of_base.base);
+	}
+/*
+ * Activate the n'th+1 timer as a stable CPU clocksource.
+ */
+	to = &rttm_cs.to;
+	to->of_base.index = clkidx;
+	timer_of_init(np, to);
+	if (rttm_cs.to.of_base.base && rttm_cs.to.of_clk.rate) {
+		clocksource_register_hz(&rttm_cs.cs, RTTM_TICKS_PER_SEC);
+		sched_clock_register(rttm_read_clock, RTTM_BIT_COUNT, RTTM_TICKS_PER_SEC);
+	} else
+		pr_err("%s: setup of timer %d as clocksoure failed", __func__, clkidx);
+
+	return cpuhp_setup_state(CPUHP_AP_REALTEK_TIMER_STARTING,
+				"timer/realtek:online",
+				rttm_cpu_starting, NULL);
+rollback:
+	pr_err("%s: timer registration failed\n", __func__);
+	for_each_possible_cpu(cpu_rollback) {
+		if (cpu_rollback == cpu)
+			break;
+		to = per_cpu_ptr(&rttm_to, cpu_rollback);
+		timer_of_cleanup(to);
+	}
+
+	return -EINVAL;
+}
+
+TIMER_OF_DECLARE(otto_timer, "realtek,otto-timer", rttm_probe);

target/linux/realtek/patches-5.10/302-clocksource-add-otto-driver.patch

@@ -0,0 +1,40 @@
+--- a/drivers/clocksource/Kconfig
++++ b/drivers/clocksource/Kconfig
+@@ -127,6 +127,17 @@ config RDA_TIMER
+ 	help
+ 	  Enables the support for the RDA Micro timer driver.
+ 
++config REALTEK_OTTO_TIMER
++	bool "Clocksource/timer for the Realtek Otto platform"
++	select COMMON_CLK
++	select TIMER_OF
++	help
++	  This driver adds support for the timers found in the Realtek RTL83xx
++	  and RTL93xx SoCs series. This includes chips such as RTL8380, RTL8381
++	  and RTL832, as well as chips from the RTL839x series, such as RTL8390
++	  RT8391, RTL8392, RTL8393 and RTL8396 and chips of the RTL930x series
++	  such as RTL9301, RTL9302 or RTL9303.
++
+ config SUN4I_TIMER
+ 	bool "Sun4i timer driver" if COMPILE_TEST
+ 	depends on HAS_IOMEM
+--- a/drivers/clocksource/Makefile
++++ b/drivers/clocksource/Makefile
+@@ -63,6 +63,7 @@ obj-$(CONFIG_MILBEAUT_TIMER)	+= timer-mi
+ obj-$(CONFIG_SPRD_TIMER)	+= timer-sprd.o
+ obj-$(CONFIG_NPCM7XX_TIMER)	+= timer-npcm7xx.o
+ obj-$(CONFIG_RDA_TIMER)		+= timer-rda.o
++obj-$(CONFIG_REALTEK_OTTO_TIMER)	+= timer-rtl-otto.o
+ 
+ obj-$(CONFIG_ARC_TIMERS)		+= arc_timer.o
+ obj-$(CONFIG_ARM_ARCH_TIMER)		+= arm_arch_timer.o
+--- a/include/linux/cpuhotplug.h
++++ b/include/linux/cpuhotplug.h
+@@ -133,6 +133,7 @@ enum cpuhp_state {
+ 	CPUHP_AP_MARCO_TIMER_STARTING,
+ 	CPUHP_AP_MIPS_GIC_TIMER_STARTING,
+ 	CPUHP_AP_ARC_TIMER_STARTING,
++	CPUHP_AP_REALTEK_TIMER_STARTING,
+ 	CPUHP_AP_RISCV_TIMER_STARTING,
+ 	CPUHP_AP_CLINT_TIMER_STARTING,
+ 	CPUHP_AP_CSKY_TIMER_STARTING,