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clocksource/drivers/arm_arch_timer: Control the evtstrm via the cmdline

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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@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
This commit is contained in:
Will Deacon 2016-06-27 17:30:13 +01:00 committed by Daniel Lezcano
parent 5cc87a4df5
commit 46fd5c6b30
3 changed files with 24 additions and 6 deletions
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8
Documentation/kernel-parameters.txt
View File

@ -687,6 +687,14 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
[SPARC64] tick [SPARC64] tick
[X86-64] hpet,tsc [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] clearcpuid=BITNUM [X86]
Disable CPUID feature X for the kernel. See Disable CPUID feature X for the kernel. See
arch/x86/include/asm/cpufeatures.h for the valid bit arch/x86/include/asm/cpufeatures.h for the valid bit

12
drivers/clocksource/Kconfig
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@ -288,14 +288,16 @@ config ARM_ARCH_TIMER
select CLKSRC_ACPI if ACPI select CLKSRC_ACPI if ACPI
config ARM_ARCH_TIMER_EVTSTREAM 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 default y if ARM_ARCH_TIMER
depends on ARM_ARCH_TIMER depends on ARM_ARCH_TIMER
help help
This option enables support for event stream generation based on This option enables support by default for event stream generation
the ARM architected timer. It is used for waking up CPUs executing based on the ARM architected timer. It is used for waking up CPUs
the wfe instruction at a frequency represented as a power-of-2 executing the wfe instruction at a frequency represented as a
divisor of the clock rate. 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 The main use of the event stream is wfe-based timeouts of userspace
locking implementations. It might also be useful for imposing timeout locking implementations. It might also be useful for imposing timeout
on wfe to safeguard against any programming errors in case an expected on wfe to safeguard against any programming errors in case an expected

10
drivers/clocksource/arm_arch_timer.c
View File

@ -79,6 +79,14 @@ static enum ppi_nr arch_timer_uses_ppi = VIRT_PPI;
static bool arch_timer_c3stop; static bool arch_timer_c3stop;
static bool arch_timer_mem_use_virtual; 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. * 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); enable_percpu_irq(arch_timer_ppi[PHYS_NONSECURE_PPI], 0);
arch_counter_set_user_access(); arch_counter_set_user_access();
if (IS_ENABLED(CONFIG_ARM_ARCH_TIMER_EVTSTREAM)) if (evtstrm_enable)
arch_timer_configure_evtstream(); arch_timer_configure_evtstream();
return 0; return 0;