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Diffstat (limited to 'Documentation/devicetree/bindings/arm/idle-states.txt')
| -rw-r--r-- | Documentation/devicetree/bindings/arm/idle-states.txt | 32 |
1 files changed, 16 insertions, 16 deletions
diff --git a/Documentation/devicetree/bindings/arm/idle-states.txt b/Documentation/devicetree/bindings/arm/idle-states.txt index 2d325bed37e5..771f5d20ae18 100644 --- a/Documentation/devicetree/bindings/arm/idle-states.txt +++ b/Documentation/devicetree/bindings/arm/idle-states.txt @@ -28,7 +28,7 @@ PM implementation to put the processor in different idle states (which include states listed above; "off" state is not an idle state since it does not have wake-up capabilities, hence it is not considered in this document). -Idle state parameters (eg entry latency) are platform specific and need to be +Idle state parameters (e.g. entry latency) are platform specific and need to be characterized with bindings that provide the required information to OS PM code so that it can build the required tables and use them at runtime. @@ -90,24 +90,24 @@ These timing parameters can be used by an OS in different circumstances. An idle CPU requires the expected min-residency time to select the most appropriate idle state based on the expected expiry time of the next IRQ -(ie wake-up) that causes the CPU to return to the EXEC phase. +(i.e. wake-up) that causes the CPU to return to the EXEC phase. An operating system scheduler may need to compute the shortest wake-up delay for CPUs in the system by detecting how long will it take to get a CPU out -of an idle state, eg: +of an idle state, e.g.: wakeup-delay = exit-latency + max(entry-latency - (now - entry-timestamp), 0) In other words, the scheduler can make its scheduling decision by selecting -(eg waking-up) the CPU with the shortest wake-up latency. -The wake-up latency must take into account the entry latency if that period +(e.g. waking-up) the CPU with the shortest wake-up delay. +The wake-up delay must take into account the entry latency if that period has not expired. The abortable nature of the PREP period can be ignored if it cannot be relied upon (e.g. the PREP deadline may occur much sooner than -the worst case since it depends on the CPU operating conditions, ie caches +the worst case since it depends on the CPU operating conditions, i.e. caches state). An OS has to reliably probe the wakeup-latency since some devices can enforce -latency constraints guarantees to work properly, so the OS has to detect the +latency constraint guarantees to work properly, so the OS has to detect the worst case wake-up latency it can incur if a CPU is allowed to enter an idle state, and possibly to prevent that to guarantee reliable device functioning. @@ -183,15 +183,15 @@ and IDLE2: Graph 2: idle states min-residency example In graph 2 above, that takes into account idle states entry/exit energy -costs, it is clear that if the idle state residency time (ie time till next +costs, it is clear that if the idle state residency time (i.e. time till next wake-up IRQ) is less than IDLE2-min-residency, IDLE1 is the better idle state choice energywise. This is mainly down to the fact that IDLE1 entry/exit energy costs are lower than IDLE2. -However, the lower power consumption (ie shallower energy curve slope) of idle -state IDLE2 implies that after a suitable time, IDLE2 becomes more energy +However, the lower power consumption (i.e. shallower energy curve slope) of +idle state IDLE2 implies that after a suitable time, IDLE2 becomes more energy efficient. The time at which IDLE2 becomes more energy efficient than IDLE1 (and other @@ -214,8 +214,8 @@ processor idle states, defined as device tree nodes, are listed. Usage: Optional - On ARM systems, it is a container of processor idle states nodes. If the system does not provide CPU - power management capabilities or the processor just - supports idle_standby an idle-states node is not + power management capabilities, or the processor just + supports idle_standby, an idle-states node is not required. Description: idle-states node is a container node, where its @@ -287,14 +287,14 @@ follows: Value type: <prop-encoded-array> Definition: u32 value representing worst case latency in microseconds required to enter the idle state. - The exit-latency-us duration may be guaranteed - only after entry-latency-us has passed. - exit-latency-us Usage: Required Value type: <prop-encoded-array> Definition: u32 value representing worst case latency in microseconds required to exit the idle state. + The exit-latency-us duration may be guaranteed + only after entry-latency-us has passed. - min-residency-us Usage: Required @@ -342,8 +342,8 @@ follows: state. In addition to the properties listed above, a state node may require - additional properties specifics to the entry-method defined in the - idle-states node, please refer to the entry-method bindings + additional properties specific to the entry-method defined in the + idle-states node. Please refer to the entry-method bindings documentation for properties definitions. =========================================== |