From: Will Deacon <will.deacon@xxxxxxx>
Disabling the eventstream can be useful for both remotely debugging a
deployed production system and development of code using WFE-based
polling loops. Whilst this can currently be controlled via a Kconfig
option (CONFIG_ARM_ARCH_TIMER_EVTSTREAM), it's often desirable to toggle
the feature on the command line, so this patch adds a new command-line
option ("clocksource.arm_arch_timer.evtstrm") to do just that. The
default behaviour is determined based on CONFIG_ARM_ARCH_TIMER_EVTSTREAM.
Cc: Marc Zyngier <marc.zyngier@xxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>
---
Documentation/kernel-parameters.txt | 8 ++++++++
drivers/clocksource/Kconfig | 12 +++++++-----
drivers/clocksource/arm_arch_timer.c | 10 +++++++++-
3 files changed, 24 insertions(+), 6 deletions(-)
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 82b42c9..2c92f1d 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -687,6 +687,14 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
[SPARC64] tick
[X86-64] hpet,tsc
+ clocksource.arm_arch_timer.evtstrm=
+ [ARM,ARM64]
+ Format: <bool>
+ Enable/disable the eventstream feature of the ARM
+ architected timer so that code using WFE-based polling
+ loops can be debugged more effectively on production
+ systems.
+
clearcpuid=BITNUM [X86]
Disable CPUID feature X for the kernel. See
arch/x86/include/asm/cpufeatures.h for the valid bit
diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
index 7acdf3d..5677886 100644
--- a/drivers/clocksource/Kconfig
+++ b/drivers/clocksource/Kconfig
@@ -288,14 +288,16 @@ config ARM_ARCH_TIMER
select CLKSRC_ACPI if ACPI
config ARM_ARCH_TIMER_EVTSTREAM
- bool "Support for ARM architected timer event stream generation"
+ bool "Enable ARM architected timer event stream generation by default"
default y if ARM_ARCH_TIMER
depends on 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.
+ This option enables support by default 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. The behaviour can also be
+ overridden on the command line using the
+ clocksource.arm_arch_timer.evtstream parameter.
The main use of the event stream is wfe-based timeouts of userspace
locking implementations. It might also be useful for imposing timeout
on wfe to safeguard against any programming errors in case an expected
diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index 9e33309..5effd30 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -79,6 +79,14 @@ static enum ppi_nr arch_timer_uses_ppi = VIRT_PPI;
static bool arch_timer_c3stop;
static bool arch_timer_mem_use_virtual;
+static bool evtstrm_enable = IS_ENABLED(CONFIG_ARM_ARCH_TIMER_EVTSTREAM);
+
+static int __init early_evtstrm_cfg(char *buf)
+{
+ return strtobool(buf, &evtstrm_enable);
+}
+early_param("clocksource.arm_arch_timer.evtstrm", early_evtstrm_cfg);
+
/*
* Architected system timer support.
*/
@@ -372,7 +380,7 @@ static int arch_timer_setup(struct clock_event_device *clk)
enable_percpu_irq(arch_timer_ppi[PHYS_NONSECURE_PPI], 0);
arch_counter_set_user_access();
- if (IS_ENABLED(CONFIG_ARM_ARCH_TIMER_EVTSTREAM))
+ if (evtstrm_enable)
arch_timer_configure_evtstream();
return 0;
--
1.9.1
--
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