From: Will Deacon <will.dea...@arm.com>
The ARM architected timer can generate events (used for waking up
CPUs executing the wfe instruction) at a frequency represented as a
power-of-2 divisor of the clock rate.
An event stream might be used:
- To impose a time-out on a wfe polling loop.
- To safeguard against any programming error in case an expected event
is not generated.
- To implement wfe-based timeouts for userspace locking implementations.
This patch computes the event stream frequency aiming for a period
of 100us between events. It uses ARM/ARM64 specific backends to configure
and enable the event stream.
Cc: Catalin Marinas <catalin.mari...@arm.com>
Cc: Lorenzo Pieralisi <lorenzo.pieral...@arm.com>
Signed-off-by: Will Deacon <will.dea...@arm.com>
[sudeep: moving ARM/ARM64 changes into separate patches
and adding Kconfig option]
Signed-off-by: Sudeep KarkadaNagesha <sudeep.karkadanage...@arm.com>
---
drivers/clocksource/Kconfig | 14 ++++++++++++++
drivers/clocksource/arm_arch_timer.c | 23 +++++++++++++++++++++++
include/clocksource/arm_arch_timer.h | 2 ++
3 files changed, 39 insertions(+)
diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
index b7b9b04..8c10d9a 100644
--- a/drivers/clocksource/Kconfig
+++ b/drivers/clocksource/Kconfig
@@ -74,6 +74,20 @@ config ARM_ARCH_TIMER
bool
select CLKSRC_OF if OF
+config ARM_ARCH_TIMER_EVTSTREAM
+ bool "Support for ARM architected timer event stream generation"
+ default y if ARM_ARCH_TIMER
+ help
+ This option enables support for event stream generation based on
+ the ARM architected timer. It is used for waking up CPUs executing
+ the wfe instruction at a frequency represented as a power-of-2
+ divisor of the clock rate. An event stream might be useful for
+ imposing timeout on a wfe, safeguarding against any programming
+ errors in case an expected event is not generated or even to
+ implement wfe-based timeouts for userspace locking implementations.
+ This can be disabled for hardware validation purposes to detect any
+ hardware anamolies of missing events.
+
config ARM_GLOBAL_TIMER
bool
select CLKSRC_OF if OF
diff --git a/drivers/clocksource/arm_arch_timer.c
b/drivers/clocksource/arm_arch_timer.c
index ffadd83..e331818 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -123,6 +123,28 @@ static int arch_timer_set_next_event_phys(unsigned long
evt,
return 0;
}
+#ifdef CONFIG_ARM_ARCH_TIMER_EVTSTREAM
+static void arch_timer_setup_evtstream(void)
+{
+ int evt_stream_div, pos;
+
+ /* Find the closest power of two to the divisor */
+ evt_stream_div = arch_timer_rate / ARCH_TIMER_EVT_STREAM_FREQ;
+ pos = fls(evt_stream_div);
+ if (pos > 1 && !(evt_stream_div & (1 << (pos - 2))))
+ pos--;
+ /* enable event stream */
+ arch_timer_evtstrm_config(true, min(pos, 15));
+ /* enable hwcap definition to the users for event stream feature */
+ arch_timer_set_hwcap_evtstrm();
+}
+#else
+static void arch_timer_setup_evtstream(void)
+{
+ arch_timer_evtstrm_config(false, 0);
+}
+#endif
+
static int arch_timer_setup(struct clock_event_device *clk)
{
clk->features = CLOCK_EVT_FEAT_ONESHOT | CLOCK_EVT_FEAT_C3STOP;
@@ -154,6 +176,7 @@ static int arch_timer_setup(struct clock_event_device *clk)
}
arch_counter_set_user_access();
+ arch_timer_setup_evtstream();
return 0;
}
diff --git a/include/clocksource/arm_arch_timer.h
b/include/clocksource/arm_arch_timer.h
index 551f7e9..c4d0fc4 100644
--- a/include/clocksource/arm_arch_timer.h
+++ b/include/clocksource/arm_arch_timer.h
@@ -37,6 +37,8 @@
#define ARCH_TIMER_USR_VT_ACCESS_EN (1 << 8) /* virtual timer registers */
#define ARCH_TIMER_USR_PT_ACCESS_EN (1 << 9) /* physical timer registers */
+#define ARCH_TIMER_EVT_STREAM_FREQ 10000 /* 100us */
+
#ifdef CONFIG_ARM_ARCH_TIMER
extern u32 arch_timer_get_rate(void);
--
1.8.1.2
--
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