[PATCH v6 4/5] drivers: clocksource: add support for ARM architected timer event stream
catalin.marinas at arm.com
Thu Aug 29 11:39:14 EDT 2013
On Thu, Aug 29, 2013 at 03:55:41PM +0100, Sudeep KarkadaNagesha wrote:
> From: Will Deacon <will.deacon at 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 at arm.com>
> Cc: Catalin Marinas <catalin.marinas at arm.com>
> Signed-off-by: Will Deacon <will.deacon at arm.com>
> [sudeep: moving ARM/ARM64 changes into separate patches
> and adding Kconfig option]
> Signed-off-by: Sudeep KarkadaNagesha <sudeep.karkadanagesha at 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
> 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
> + 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 at arm.com>
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