From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sudeep.KarkadaNagesha@arm.com (Sudeep KarkadaNagesha) Date: Thu, 29 Aug 2013 16:42:23 +0100 Subject: [PATCH v6 4/5] drivers: clocksource: add support for ARM architected timer event stream In-Reply-To: <20130829153914.GA10707@darko.cambridge.arm.com> References: <1377788142-21388-1-git-send-email-Sudeep.KarkadaNagesha@arm.com> <1377788142-21388-5-git-send-email-Sudeep.KarkadaNagesha@arm.com> <20130829153914.GA10707@darko.cambridge.arm.com> Message-ID: <521F6BDF.2050909@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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 >> >> 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 >> Cc: Catalin Marinas >> 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 | 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 > Thanks. Regards, Sudeep