Re: [PATCH v2 1/3] drivers: clocksource: configure event stream forARM arch timer

From: Catalin Marinas
Date: Tue Jul 23 2013 - 06:24:14 EST


On Mon, Jul 22, 2013 at 12:21:20PM +0100, Sudeep KarkadaNagesha wrote:
> From: Will Deacon <will.deacon@xxxxxxx>
>
> 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.
>
> This patch configures the event stream, aiming for a period of 100us
> between events. This can be used to implement wfe-based timeouts for
> userspace locking implementations.
...
> --- a/include/clocksource/arm_arch_timer.h
> +++ b/include/clocksource/arm_arch_timer.h
> @@ -29,6 +29,8 @@
> #define ARCH_TIMER_PHYS_ACCESS 0
> #define ARCH_TIMER_VIRT_ACCESS 1
>
> +#define ARCH_TIMER_EVT_STREAM_FREQ 10000 /* 100us */

BTW, if user-space starts using this, it will become an ABI. Is this the
right frequency?

In addition, do we want to expose this via hwcap? Something like
HWCAP_EVSTR100US?

--
Catalin
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