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authorSerge Semin <Sergey.Semin@baikalelectronics.ru>2020-05-21 23:48:17 +0300
committerDaniel Lezcano <daniel.lezcano@linaro.org>2020-05-23 01:03:16 +0300
commit7d7de1a65349811b24971c5e8e040e6aac192dd4 (patch)
treeafdcf8929288d68c257b33529a1ca1571f18a5ca /drivers/clocksource
parent48016e78d328998b1f00bcfb639adeabca51abe5 (diff)
downloadlinux-7d7de1a65349811b24971c5e8e040e6aac192dd4.tar.xz
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
Diffstat (limited to 'drivers/clocksource')
-rw-r--r--drivers/clocksource/Kconfig1
-rw-r--r--drivers/clocksource/mips-gic-timer.c19
2 files changed, 19 insertions, 1 deletions
diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
index c82400273b0a..91418381fcd4 100644
--- a/drivers/clocksource/Kconfig
+++ b/drivers/clocksource/Kconfig
@@ -570,6 +570,7 @@ config CLKSRC_VERSATILE
config CLKSRC_MIPS_GIC
bool
depends on MIPS_GIC
+ select CLOCKSOURCE_WATCHDOG
select TIMER_OF
config CLKSRC_TANGO_XTAL
diff --git a/drivers/clocksource/mips-gic-timer.c b/drivers/clocksource/mips-gic-timer.c
index ef12c12c2432..be4175f415ba 100644
--- a/drivers/clocksource/mips-gic-timer.c
+++ b/drivers/clocksource/mips-gic-timer.c
@@ -24,6 +24,9 @@
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)
{
@@ -125,8 +128,10 @@ static int gic_clk_notifier(struct notifier_block *nb, unsigned long action,
{
struct clk_notifier_data *cnd = data;
- if (action == POST_RATE_CHANGE)
+ 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;
}
@@ -172,6 +177,18 @@ static struct clocksource gic_clocksource = {
.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;