From: Will Deacon <[email protected]> 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 <[email protected]> Cc: Mark Rutland <[email protected]> Signed-off-by: Will Deacon <[email protected]> Signed-off-by: Daniel Lezcano <[email protected]> --- 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
