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Commit 46fd5c6b authored by Will Deacon's avatar Will Deacon Committed by Daniel Lezcano
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clocksource/drivers/arm_arch_timer: Control the evtstrm via the cmdline 



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: default avatarWill Deacon <will.deacon@arm.com>
Signed-off-by: default avatarDaniel Lezcano <daniel.lezcano@linaro.org>
parent 5cc87a4d

Documentation/kernel-parameters.txt

+8 −0
Original line number Diff line number Diff line
@@ -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

drivers/clocksource/Kconfig

+7 −5
Original line number Diff line number Diff line
@@ -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

drivers/clocksource/arm_arch_timer.c

+9 −1
Original line number Diff line number Diff line
@@ -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;