From 037f637767a82907efedda78d3ff405c34020075 Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Fri, 23 Aug 2013 15:32:29 +0100 Subject: drivers: clocksource: add support for ARM architected timer event stream 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 implement wfe-based timeouts for userspace locking implementations. - To impose a timeout on a wfe for safeguarding against any programming error in case an expected event is not generated. 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: Lorenzo Pieralisi Reviewed-by: Catalin Marinas Acked-by: Olof Johansson Signed-off-by: Will Deacon [sudeep: moving ARM/ARM64 changes into separate patches and adding Kconfig option] Signed-off-by: Sudeep KarkadaNagesha --- drivers/clocksource/Kconfig | 15 +++++++++++++++ drivers/clocksource/arm_arch_timer.c | 15 +++++++++++++++ include/clocksource/arm_arch_timer.h | 2 ++ 3 files changed, 32 insertions(+) diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig index 41c69469ce20..559d80335446 100644 --- a/drivers/clocksource/Kconfig +++ b/drivers/clocksource/Kconfig @@ -74,6 +74,21 @@ 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. + 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 + event is not generated. + This must be disabled for hardware validation purposes to detect any + hardware anomalies 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 fbd9ccd5e114..105f8ffa66a8 100644 --- a/drivers/clocksource/arm_arch_timer.c +++ b/drivers/clocksource/arm_arch_timer.c @@ -294,6 +294,19 @@ static void __arch_timer_setup(unsigned type, clockevents_config_and_register(clk, arch_timer_rate, 0xf, 0x7fffffff); } +static void arch_timer_configure_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_enable(min(pos, 15)); +} + static int arch_timer_setup(struct clock_event_device *clk) { __arch_timer_setup(ARCH_CP15_TIMER, clk); @@ -307,6 +320,8 @@ static int arch_timer_setup(struct clock_event_device *clk) } arch_counter_set_user_access(); + if (IS_ENABLED(CONFIG_ARM_ARCH_TIMER_EVTSTREAM)) + arch_timer_configure_evtstream(); return 0; } diff --git a/include/clocksource/arm_arch_timer.h b/include/clocksource/arm_arch_timer.h index 8707dae4cee2..6d26b40cbf5d 100644 --- a/include/clocksource/arm_arch_timer.h +++ b/include/clocksource/arm_arch_timer.h @@ -41,6 +41,8 @@ enum arch_timer_reg { #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); -- cgit v1.2.3