lkml.org 
[lkml]   [2013]   [Aug]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v6 4/5] drivers: clocksource: add support for ARM architected timer event stream
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>


\
 
 \ /
  Last update: 2013-08-29 19:21    [W:0.457 / U:0.032 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site