| Message ID | 1377788142-21388-5-git-send-email-Sudeep.KarkadaNagesha@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Thu, Aug 29, 2013 at 03:55:41PM +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 | 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. I would be a bit more assertive here, something like "the main use of the event stream is wfe-based timeouts of 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 Maybe "imposting timeout on wfe to safeguard against ...". We already mentioned wfe-based timeout above. Otherwise, for the whole series: Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
On 29/08/13 16:39, Catalin Marinas wrote: > On Thu, Aug 29, 2013 at 03:55:41PM +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 | 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. > > I would be a bit more assertive here, something like "the main use of > the event stream is wfe-based timeouts of 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 > > Maybe "imposting timeout on wfe to safeguard against ...". We already > mentioned wfe-based timeout above. > Ok will fix this Kconfig description. > Otherwise, for the whole series: > > Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> > Thanks. Regards, Sudeep
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);