Messages in this thread Patch in this message | | | From | Sudeep KarkadaNagesha <> | Subject | [PATCH v6 4/5] drivers: clocksource: add support for ARM architected timer event stream | Date | Thu, 29 Aug 2013 15:55:41 +0100 |
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From: Will Deacon <will.deacon@arm.com>
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 impose a time-out on a wfe polling loop. - To safeguard against any programming error in case an expected event is not generated. - To implement wfe-based timeouts for userspace locking implementations.
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 <lorenzo.pieralisi@arm.com> Cc: Catalin Marinas <catalin.marinas@arm.com> Signed-off-by: Will Deacon <will.deacon@arm.com> [sudeep: moving ARM/ARM64 changes into separate patches and adding Kconfig option] Signed-off-by: Sudeep KarkadaNagesha <sudeep.karkadanagesha@arm.com> --- drivers/clocksource/Kconfig | 14 ++++++++++++++ drivers/clocksource/arm_arch_timer.c | 15 +++++++++++++++ include/clocksource/arm_arch_timer.h | 2 ++ 3 files changed, 31 insertions(+)
diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig index b7b9b04..49f1f6e 100644 --- a/drivers/clocksource/Kconfig +++ b/drivers/clocksource/Kconfig @@ -74,6 +74,20 @@ 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. An event stream might be mainly useful + for wfe-based timeouts for userspace locking implementations. + It might also be useful for imposing timeout on a wfe or even + safeguarding 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 ffadd83..9777b36 100644 --- a/drivers/clocksource/arm_arch_timer.c +++ b/drivers/clocksource/arm_arch_timer.c @@ -123,6 +123,19 @@ static int arch_timer_set_next_event_phys(unsigned long evt, return 0; } +static void arch_timer_enable_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) { clk->features = CLOCK_EVT_FEAT_ONESHOT | CLOCK_EVT_FEAT_C3STOP; @@ -154,6 +167,8 @@ 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_enable_evtstream(); return 0; } diff --git a/include/clocksource/arm_arch_timer.h b/include/clocksource/arm_arch_timer.h index 551f7e9..c4d0fc4 100644 --- a/include/clocksource/arm_arch_timer.h +++ b/include/clocksource/arm_arch_timer.h @@ -37,6 +37,8 @@ #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); -- 1.8.1.2
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