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authorLorenzo Pieralisi <lorenzo.pieralisi@arm.com>2014-04-08 10:04:32 +0100
committerDaniel Lezcano <daniel.lezcano@linaro.org>2014-04-29 15:06:36 +0200
commit82a5619410d4c4df65c04272db198eca5a867c18 (patch)
tree979fe711832417f1ff2ed9d31a69d804f5393483 /Documentation
parent27630532ef5ead28b98cfe28d8f95222ef91c2b7 (diff)
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clocksource: arch_arm_timer: Fix age-old arch timer C3STOP detection issue
ARM arch timers are tightly coupled with the CPU logic and lose context on platform implementing HW power management when cores are powered down at run-time. Marking the arch timers as C3STOP regardless of power management capabilities causes issues on platforms with no power management, since in that case the arch timers cannot possibly enter states where the timer loses context at runtime and therefore can always be used as a high resolution clockevent device. In order to fix the C3STOP issue in a way compliant with how real HW works, this patch adds a boolean property to the arch timer bindings to define if the arch timer is managed by an always-on power domain. This power domain is present on all ARM platforms to date, and manages HW that must not be turned off, whatever the state of other HW components (eg power controller). On platforms with no power management capabilities, it is the only power domain present, which encompasses and manages power supply for all HW components in the system. If the timer is powered by the always-on power domain, the always-on property must be present in the bindings which means that the timer cannot be shutdown at runtime, so it is not a C3STOP clockevent device. If the timer binding does not contain the always-on property, the timer is assumed to be power-gateable, hence it must be defined as a C3STOP clockevent device. Cc: Daniel Lezcano <daniel.lezcano@linaro.org> Cc: Magnus Damm <damm@opensource.se> Cc: Marc Carino <marc.ceeeee@gmail.com> Cc: Mark Rutland <mark.rutland@arm.com> Acked-by: Marc Zyngier <marc.zyngier@arm.com> Acked-by: Rob Herring <robh@kernel.org> Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com> Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/devicetree/bindings/arm/arch_timer.txt3
1 files changed, 3 insertions, 0 deletions
diff --git a/Documentation/devicetree/bindings/arm/arch_timer.txt b/Documentation/devicetree/bindings/arm/arch_timer.txt
index 06fc760..37b2caf 100644
--- a/Documentation/devicetree/bindings/arm/arch_timer.txt
+++ b/Documentation/devicetree/bindings/arm/arch_timer.txt
@@ -19,6 +19,9 @@ to deliver its interrupts via SPIs.
- clock-frequency : The frequency of the main counter, in Hz. Optional.
+- always-on : a boolean property. If present, the timer is powered through an
+ always-on power domain, therefore it never loses context.
+
Example:
timer {
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