linux/drivers/clocksource/mips-gic-timer.c
Serge Semin 7d7de1a653 clocksource: mips-gic-timer: Mark GIC timer as unstable if ref clock changes
Currently clocksource framework doesn't support the clocks with variable
frequency. Since MIPS GIC timer ticks rate might be unstable on some
platforms, we must make sure that it justifies the clocksource
requirements. MIPS GIC timer is incremented with the CPU cluster reference
clocks rate. So in case if CPU frequency changes, the MIPS GIC tick rate
changes synchronously. Due to this the clocksource subsystem can't rely on
the timer to measure system clocks anymore. This commit marks the MIPS GIC
based clocksource as unstable if reference clock (normally it's a CPU
reference clocks) rate changes. The clocksource will execute a watchdog
thread, which lowers the MIPS GIC timer rating to zero and fallbacks to a
new stable one.

Note we don't need to set the CLOCK_SOURCE_MUST_VERIFY flag to the MIPS
GIC clocksource since normally the timer is stable. The only reason why
it gets unstable is due to the ref clock rate change, which event we
detect here in the driver by means of the clocks event notifier.

Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Cc: Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Paul Burton <paulburton@kernel.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: linux-mips@vger.kernel.org
Cc: linux-rtc@vger.kernel.org
Cc: devicetree@vger.kernel.org
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20200521204818.25436-9-Sergey.Semin@baikalelectronics.ru
2020-05-23 00:03:16 +02:00

275 lines
6.3 KiB
C

/*
* 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.
*
* Copyright (C) 2012 MIPS Technologies, Inc. All rights reserved.
*/
#define pr_fmt(fmt) "mips-gic-timer: " fmt
#include <linux/clk.h>
#include <linux/clockchips.h>
#include <linux/cpu.h>
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/notifier.h>
#include <linux/of_irq.h>
#include <linux/percpu.h>
#include <linux/sched_clock.h>
#include <linux/smp.h>
#include <linux/time.h>
#include <asm/mips-cps.h>
static DEFINE_PER_CPU(struct clock_event_device, gic_clockevent_device);
static int gic_timer_irq;
static unsigned int gic_frequency;
static bool __read_mostly gic_clock_unstable;
static void gic_clocksource_unstable(char *reason);
static u64 notrace gic_read_count_2x32(void)
{
unsigned int hi, hi2, lo;
do {
hi = read_gic_counter_32h();
lo = read_gic_counter_32l();
hi2 = read_gic_counter_32h();
} while (hi2 != hi);
return (((u64) hi) << 32) + lo;
}
static u64 notrace gic_read_count_64(void)
{
return read_gic_counter();
}
static u64 notrace gic_read_count(void)
{
if (mips_cm_is64)
return gic_read_count_64();
return gic_read_count_2x32();
}
static int gic_next_event(unsigned long delta, struct clock_event_device *evt)
{
int cpu = cpumask_first(evt->cpumask);
u64 cnt;
int res;
cnt = gic_read_count();
cnt += (u64)delta;
if (cpu == raw_smp_processor_id()) {
write_gic_vl_compare(cnt);
} else {
write_gic_vl_other(mips_cm_vp_id(cpu));
write_gic_vo_compare(cnt);
}
res = ((int)(gic_read_count() - cnt) >= 0) ? -ETIME : 0;
return res;
}
static irqreturn_t gic_compare_interrupt(int irq, void *dev_id)
{
struct clock_event_device *cd = dev_id;
write_gic_vl_compare(read_gic_vl_compare());
cd->event_handler(cd);
return IRQ_HANDLED;
}
static struct irqaction gic_compare_irqaction = {
.handler = gic_compare_interrupt,
.percpu_dev_id = &gic_clockevent_device,
.flags = IRQF_PERCPU | IRQF_TIMER,
.name = "timer",
};
static void gic_clockevent_cpu_init(unsigned int cpu,
struct clock_event_device *cd)
{
cd->name = "MIPS GIC";
cd->features = CLOCK_EVT_FEAT_ONESHOT |
CLOCK_EVT_FEAT_C3STOP;
cd->rating = 350;
cd->irq = gic_timer_irq;
cd->cpumask = cpumask_of(cpu);
cd->set_next_event = gic_next_event;
clockevents_config_and_register(cd, gic_frequency, 0x300, 0x7fffffff);
enable_percpu_irq(gic_timer_irq, IRQ_TYPE_NONE);
}
static void gic_clockevent_cpu_exit(struct clock_event_device *cd)
{
disable_percpu_irq(gic_timer_irq);
}
static void gic_update_frequency(void *data)
{
unsigned long rate = (unsigned long)data;
clockevents_update_freq(this_cpu_ptr(&gic_clockevent_device), rate);
}
static int gic_starting_cpu(unsigned int cpu)
{
gic_clockevent_cpu_init(cpu, this_cpu_ptr(&gic_clockevent_device));
return 0;
}
static int gic_clk_notifier(struct notifier_block *nb, unsigned long action,
void *data)
{
struct clk_notifier_data *cnd = data;
if (action == POST_RATE_CHANGE) {
gic_clocksource_unstable("ref clock rate change");
on_each_cpu(gic_update_frequency, (void *)cnd->new_rate, 1);
}
return NOTIFY_OK;
}
static int gic_dying_cpu(unsigned int cpu)
{
gic_clockevent_cpu_exit(this_cpu_ptr(&gic_clockevent_device));
return 0;
}
static struct notifier_block gic_clk_nb = {
.notifier_call = gic_clk_notifier,
};
static int gic_clockevent_init(void)
{
int ret;
if (!gic_frequency)
return -ENXIO;
ret = setup_percpu_irq(gic_timer_irq, &gic_compare_irqaction);
if (ret < 0) {
pr_err("IRQ %d setup failed (%d)\n", gic_timer_irq, ret);
return ret;
}
cpuhp_setup_state(CPUHP_AP_MIPS_GIC_TIMER_STARTING,
"clockevents/mips/gic/timer:starting",
gic_starting_cpu, gic_dying_cpu);
return 0;
}
static u64 gic_hpt_read(struct clocksource *cs)
{
return gic_read_count();
}
static struct clocksource gic_clocksource = {
.name = "GIC",
.read = gic_hpt_read,
.flags = CLOCK_SOURCE_IS_CONTINUOUS,
.vdso_clock_mode = VDSO_CLOCKMODE_GIC,
};
static void gic_clocksource_unstable(char *reason)
{
if (gic_clock_unstable)
return;
gic_clock_unstable = true;
pr_info("GIC timer is unstable due to %s\n", reason);
clocksource_mark_unstable(&gic_clocksource);
}
static int __init __gic_clocksource_init(void)
{
unsigned int count_width;
int ret;
/* Set clocksource mask. */
count_width = read_gic_config() & GIC_CONFIG_COUNTBITS;
count_width >>= __ffs(GIC_CONFIG_COUNTBITS);
count_width *= 4;
count_width += 32;
gic_clocksource.mask = CLOCKSOURCE_MASK(count_width);
/* Calculate a somewhat reasonable rating value. */
gic_clocksource.rating = 200 + gic_frequency / 10000000;
ret = clocksource_register_hz(&gic_clocksource, gic_frequency);
if (ret < 0)
pr_warn("Unable to register clocksource\n");
return ret;
}
static int __init gic_clocksource_of_init(struct device_node *node)
{
struct clk *clk;
int ret;
if (!mips_gic_present() || !node->parent ||
!of_device_is_compatible(node->parent, "mti,gic")) {
pr_warn("No DT definition\n");
return -ENXIO;
}
clk = of_clk_get(node, 0);
if (!IS_ERR(clk)) {
ret = clk_prepare_enable(clk);
if (ret < 0) {
pr_err("Failed to enable clock\n");
clk_put(clk);
return ret;
}
gic_frequency = clk_get_rate(clk);
} else if (of_property_read_u32(node, "clock-frequency",
&gic_frequency)) {
pr_err("Frequency not specified\n");
return -EINVAL;
}
gic_timer_irq = irq_of_parse_and_map(node, 0);
if (!gic_timer_irq) {
pr_err("IRQ not specified\n");
return -EINVAL;
}
ret = __gic_clocksource_init();
if (ret)
return ret;
ret = gic_clockevent_init();
if (!ret && !IS_ERR(clk)) {
if (clk_notifier_register(clk, &gic_clk_nb) < 0)
pr_warn("Unable to register clock notifier\n");
}
/* And finally start the counter */
clear_gic_config(GIC_CONFIG_COUNTSTOP);
/*
* It's safe to use the MIPS GIC timer as a sched clock source only if
* its ticks are stable, which is true on either the platforms with
* stable CPU frequency or on the platforms with CM3 and CPU frequency
* change performed by the CPC core clocks divider.
*/
if (mips_cm_revision() >= CM_REV_CM3 || !IS_ENABLED(CONFIG_CPU_FREQ)) {
sched_clock_register(mips_cm_is64 ?
gic_read_count_64 : gic_read_count_2x32,
64, gic_frequency);
}
return 0;
}
TIMER_OF_DECLARE(mips_gic_timer, "mti,gic-timer",
gic_clocksource_of_init);