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drivers: clocksource: add support for ARM architected timer event stream

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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 implement wfe-based timeouts for userspace locking implementations.
- To impose a timeout on a wfe for safeguarding against any programming
  error in case an expected event is not generated.

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>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Olof Johansson <olof@lixom.net>
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>
This commit is contained in:
Will Deacon 2013-08-23 15:32:29 +01:00 committed by Sudeep KarkadaNagesha
parent 46efe547ac
commit 037f637767
3 changed files with 32 additions and 0 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

15
drivers/clocksource/Kconfig
View file

@ -74,6 +74,21 @@ 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.
The main use of the event stream is wfe-based timeouts of userspace
locking implementations. It might also be useful for imposing timeout
on wfe to safeguard 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

15
drivers/clocksource/arm_arch_timer.c
View file

@ -294,6 +294,19 @@ static void __arch_timer_setup(unsigned type,
clockevents_config_and_register(clk, arch_timer_rate, 0xf, 0x7fffffff);
}
static void arch_timer_configure_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)
{
__arch_timer_setup(ARCH_CP15_TIMER, clk);
@ -307,6 +320,8 @@ 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_configure_evtstream();
return 0;
}

2
include/clocksource/arm_arch_timer.h
View file

@ -41,6 +41,8 @@ enum arch_timer_reg {
#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);