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Subject[PATCH 1/4] clocksource: dw_apb_timer: Set clockevent any-possible-CPU mask
From: Serge Semin <>

Currently the DW APB Timer driver binds all clockevent timers to
CPU #0. This isn't good for multiple reasons. First of all seeing
the device is placed on APB bus (which makes it accessible from any
CPU core), accessible over MMIO and having the DYNIRQ flag set we
can be sure that manually binding the timer to any CPU just isn't
correct. By doing so we just set an extra limitation on device usage.
This also doesn't reflect the device actual capability, since by
setting the IRQ affinity we can make it virtually local to any CPU.
Secondly imagine if you had a real CPU-local timer with the same
rating and the same CPU-affinity. In this case if DW APB timer was
registered first, then due to the clockevent framework tick-timer
selection procedure we'll end up with the real CPU-local timer being
left unselected for clock-events tracking. But on most of the platforms
(MIPS/ARM/etc) such timers are normally embedded into the CPU core and
are accessible with much better performance then devices placed on APB.
For instance in MIPS architectures there is r4k-timer, which is
CPU-local, assigned with the same rating, and normally its
clockevent device is registered after the platform-specific one.

So in order to fix all of these issues lets set the DW APB clockevent
timer cpumask to be 'cpu_possible_mask'. By doing so the clockevent
framework would prefer to select the real CPU-local timer instead
of DW APB one. Otherwise if there is no other than DW APB device for
clockevents tracking then it will be selected.

Signed-off-by: Serge Semin <>
Signed-off-by: Alexey Malahov <>
Cc: Thomas Bogendoerfer <>
Cc: Paul Burton <>
Cc: Ralf Baechle <>
drivers/clocksource/dw_apb_timer.c | 18 +++++++-----------
drivers/clocksource/dw_apb_timer_of.c | 3 +--
include/linux/dw_apb_timer.h | 2 +-
3 files changed, 9 insertions(+), 14 deletions(-)

diff --git a/drivers/clocksource/dw_apb_timer.c b/drivers/clocksource/dw_apb_timer.c
index 654766538f93..f213bcb4cf71 100644
--- a/drivers/clocksource/dw_apb_timer.c
+++ b/drivers/clocksource/dw_apb_timer.c
@@ -106,6 +106,7 @@ static irqreturn_t dw_apb_clockevent_irq(int irq, void *data)


@@ -123,8 +124,7 @@ static int apbt_shutdown(struct clock_event_device *evt)
struct dw_apb_clock_event_device *dw_ced = ced_to_dw_apb_ced(evt);
u32 ctrl;

- pr_debug("%s CPU %d state=shutdown\n", __func__,
- cpumask_first(evt->cpumask));
+ pr_debug("%s state=shutdown\n", __func__);

ctrl = apbt_readl(&dw_ced->timer, APBTMR_N_CONTROL);
@@ -137,8 +137,7 @@ static int apbt_set_oneshot(struct clock_event_device *evt)
struct dw_apb_clock_event_device *dw_ced = ced_to_dw_apb_ced(evt);
u32 ctrl;

- pr_debug("%s CPU %d state=oneshot\n", __func__,
- cpumask_first(evt->cpumask));
+ pr_debug("%s state=oneshot\n", __func__);

ctrl = apbt_readl(&dw_ced->timer, APBTMR_N_CONTROL);
@@ -170,8 +169,7 @@ static int apbt_set_periodic(struct clock_event_device *evt)
unsigned long period = DIV_ROUND_UP(dw_ced->timer.freq, HZ);
u32 ctrl;

- pr_debug("%s CPU %d state=periodic\n", __func__,
- cpumask_first(evt->cpumask));
+ pr_debug("%s state=periodic\n", __func__);

ctrl = apbt_readl(&dw_ced->timer, APBTMR_N_CONTROL);
@@ -194,8 +192,7 @@ static int apbt_resume(struct clock_event_device *evt)
struct dw_apb_clock_event_device *dw_ced = ced_to_dw_apb_ced(evt);

- pr_debug("%s CPU %d state=resume\n", __func__,
- cpumask_first(evt->cpumask));
+ pr_debug("%s state=resume\n", __func__);

return 0;
@@ -222,7 +219,6 @@ static int apbt_next_event(unsigned long delta,
* dw_apb_clockevent_init() - use an APB timer as a clock_event_device
- * @cpu: The CPU the events will be targeted at.
* @name: The name used for the timer and the IRQ for it.
* @rating: The rating to give the timer.
* @base: I/O base for the timer registers.
@@ -237,7 +233,7 @@ static int apbt_next_event(unsigned long delta,
* releasing the IRQ.
struct dw_apb_clock_event_device *
-dw_apb_clockevent_init(int cpu, const char *name, unsigned rating,
+dw_apb_clockevent_init(const char *name, unsigned int rating,
void __iomem *base, int irq, unsigned long freq)
struct dw_apb_clock_event_device *dw_ced =
@@ -257,7 +253,7 @@ dw_apb_clockevent_init(int cpu, const char *name, unsigned rating,
dw_ced->ced.max_delta_ticks = 0x7fffffff;
dw_ced->ced.min_delta_ns = clockevent_delta2ns(5000, &dw_ced->ced);
dw_ced->ced.min_delta_ticks = 5000;
- dw_ced->ced.cpumask = cpumask_of(cpu);
+ dw_ced->ced.cpumask = cpu_possible_mask;
dw_ced->ced.features = CLOCK_EVT_FEAT_PERIODIC |
dw_ced->ced.set_state_shutdown = apbt_shutdown;
diff --git a/drivers/clocksource/dw_apb_timer_of.c b/drivers/clocksource/dw_apb_timer_of.c
index 8c28b127759f..0a2505b323d7 100644
--- a/drivers/clocksource/dw_apb_timer_of.c
+++ b/drivers/clocksource/dw_apb_timer_of.c
@@ -73,8 +73,7 @@ static void __init add_clockevent(struct device_node *event_timer)

timer_get_base_and_rate(event_timer, &iobase, &rate);

- ced = dw_apb_clockevent_init(0, event_timer->name, 300, iobase, irq,
- rate);
+ ced = dw_apb_clockevent_init(event_timer->name, 300, iobase, irq, rate);
if (!ced)
panic("Unable to initialise clockevent device");

diff --git a/include/linux/dw_apb_timer.h b/include/linux/dw_apb_timer.h
index 14f072edbca5..2f3597a199bb 100644
--- a/include/linux/dw_apb_timer.h
+++ b/include/linux/dw_apb_timer.h
@@ -40,7 +40,7 @@ void dw_apb_clockevent_resume(struct dw_apb_clock_event_device *dw_ced);
void dw_apb_clockevent_stop(struct dw_apb_clock_event_device *dw_ced);

struct dw_apb_clock_event_device *
-dw_apb_clockevent_init(int cpu, const char *name, unsigned rating,
+dw_apb_clockevent_init(const char *name, unsigned int rating,
void __iomem *base, int irq, unsigned long freq);
struct dw_apb_clocksource *
dw_apb_clocksource_init(unsigned rating, const char *name, void __iomem *base,
 \ /
  Last update: 2020-03-06 13:57    [W:0.043 / U:0.300 seconds]
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