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authorRussell King <rmk+kernel@arm.linux.org.uk>2010-12-15 19:23:07 +0000
committerRussell King <rmk+kernel@arm.linux.org.uk>2010-12-22 22:44:43 +0000
commit112f38a4a31668eb6a7d91d128296a26afdf7c4b (patch)
tree9f5ce228978cf13c9e23a4762b062733ff0cbcd5 /arch/arm/Kconfig
parentb5776c4a6d0afc13697e8452b9ebe1cc4d961b74 (diff)
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ARM: sched_clock: provide common infrastructure for sched_clock()
Provide common sched_clock() infrastructure for platforms to use to create a 64-bit ns based sched_clock() implementation from a counter running at a non-variable clock rate. This implementation is based upon maintaining an epoch for the counter and an epoch for the nanosecond time. When we desire a sched_clock() time, we calculate the number of counter ticks since the last epoch update, convert this to nanoseconds and add to the epoch nanoseconds. We regularly refresh these epochs within the counter wrap interval. We perform a similar calculation as above, and store the new epochs. We read and write the epochs in such a way that sched_clock() can easily (and locklessly) detect when an update is in progress, and repeat the loading of these constants when they're known not to be stable. The one caveat is that sched_clock() is not called in the middle of an update. We achieve that by disabling IRQs. Finally, if the clock rate is known at compile time, the counter to ns conversion factors can be specified, allowing sched_clock() to be tightly optimized. We ensure that these factors are correct by providing an initialization function which performs a run-time check. Acked-by: Peter Zijlstra <peterz@infradead.org> Tested-by: Santosh Shilimkar <santosh.shilimkar@ti.com> Tested-by: Will Deacon <will.deacon@arm.com> Tested-by: Mikael Pettersson <mikpe@it.uu.se> Tested-by: Eric Miao <eric.y.miao@gmail.com> Tested-by: Olof Johansson <olof@lixom.net> Tested-by: Jamie Iles <jamie@jamieiles.com> Reviewed-by: Nicolas Pitre <nicolas.pitre@linaro.org> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Diffstat (limited to 'arch/arm/Kconfig')
-rw-r--r--arch/arm/Kconfig3
1 files changed, 3 insertions, 0 deletions
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 49778bb43782..ed7a0a729d9c 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -38,6 +38,9 @@ config HAVE_PWM
config SYS_SUPPORTS_APM_EMULATION
bool
+config HAVE_SCHED_CLOCK
+ bool
+
config GENERIC_GPIO
bool