| Message ID | 1377686689-30828-5-git-send-email-Sudeep.KarkadaNagesha@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Wed, Aug 28, 2013 at 11:44:48AM +0100, Sudeep KarkadaNagesha wrote: > 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 | 21 +++++++++++++++++++++ > include/clocksource/arm_arch_timer.h | 2 ++ > 3 files changed, 37 insertions(+) > > diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig > index b7b9b04..74946ca 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 useful for > + imposing timeout on a wfe, safeguarding against any programming > + errors in case an expected event is not generated or even to > + implement wfe-based timeouts for userspace locking implementations. > + This can be disabled for hardware validation purposes to detect any > + hardware anomalies of missing events. Maybe we should reorder this a bit and make the wfe-based timeouts as the main reason. > + > 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..f42bef4 100644 > --- a/drivers/clocksource/arm_arch_timer.c > +++ b/drivers/clocksource/arm_arch_timer.c > @@ -123,6 +123,26 @@ static int arch_timer_set_next_event_phys(unsigned long evt, > return 0; > } > > +#ifdef CONFIG_ARM_ARCH_TIMER_EVTSTREAM > +static void arch_timer_setup_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_config(true, min(pos, 15)); > +} > +#else > +static void arch_timer_setup_evtstream(void) > +{ > + arch_timer_evtstrm_config(false, 0); > +} > +#endif I think we only need an arch_timer_evtstrm_enable() function without the bool argument. We don't need to disable it at run-time. > + > static int arch_timer_setup(struct clock_event_device *clk) > { > clk->features = CLOCK_EVT_FEAT_ONESHOT | CLOCK_EVT_FEAT_C3STOP; > @@ -154,6 +174,7 @@ static int arch_timer_setup(struct clock_event_device *clk) > } > > arch_counter_set_user_access(); > + arch_timer_setup_evtstream(); and here just: if (IS_ENABLED(CONFIG_ARM_ARCH_TIMER_EVTSTREAM)) arch_timer_evtstrm_enable();
diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig index b7b9b04..74946ca 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 useful for + imposing timeout on a wfe, safeguarding against any programming + errors in case an expected event is not generated or even to + implement wfe-based timeouts for userspace locking implementations. + This can 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..f42bef4 100644 --- a/drivers/clocksource/arm_arch_timer.c +++ b/drivers/clocksource/arm_arch_timer.c @@ -123,6 +123,26 @@ static int arch_timer_set_next_event_phys(unsigned long evt, return 0; } +#ifdef CONFIG_ARM_ARCH_TIMER_EVTSTREAM +static void arch_timer_setup_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_config(true, min(pos, 15)); +} +#else +static void arch_timer_setup_evtstream(void) +{ + arch_timer_evtstrm_config(false, 0); +} +#endif + static int arch_timer_setup(struct clock_event_device *clk) { clk->features = CLOCK_EVT_FEAT_ONESHOT | CLOCK_EVT_FEAT_C3STOP; @@ -154,6 +174,7 @@ static int arch_timer_setup(struct clock_event_device *clk) } arch_counter_set_user_access(); + arch_timer_setup_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);