idle: add infrastructure for tickless support in nanokernels

An architecture that supports tickless idle in the nanokernel can allow
selecting TICKLESS_IDLE by forcing NANOKERNEL_TICKLESS_IDLE_SUPPORTED to
be enabled.

Change-Id: I4e45b619c599913d40b7bc19902094fb361b1e3b
Signed-off-by: Benjamin Walsh <benjamin.walsh@windriver.com>
Signed-off-by: Peter Mitsis <peter.mitsis@windriver.com>

kernel/Kconfig

@@ -182,28 +182,72 @@ endmenu
 endmenu
 source "kernel/nanokernel/Kconfig"
 
+config ADVANCED_POWER_MANAGEMENT
+	bool
+	prompt "Advanced power management"
+	default n
+	help
+	This option enables the platform to implement extra power management
+	policies whenever the kernel becomes idle. The kernel invokes
+	_sys_power_save_idle() to inform the power management subsystem of the
+	number of ticks until the next kernel timer is due to expire.
+
+menu "Advanced Power Management Features"
+	depends on ADVANCED_POWER_MANAGEMENT
+
+config  ADVANCED_IDLE
+	bool
+	prompt "Advanced idle state"
+	default n
+	depends on MICROKERNEL && ADVANCED_POWER_MANAGEMENT && ADVANCED_IDLE_SUPPORTED
+	help
+	This option enables the kernel to interface to a custom advanced idle
+	power saving manager. This permits the system to enter a custom
+	power saving state when the kernel becomes idle for extended periods,
+	and then to restore the system to its previous state (rather than
+	booting up from scratch) when the kernel is re-activated.
+
+config ADV_IDLE_STACK_SIZE
+	int
+	prompt "Advanced idle state stack size"
+	default 16
+	depends on ADVANCED_IDLE
+	help
+	This option defines the size of the separate stack used during the
+	system state check while the booting up. A separate stack is used
+	to avoid memory corruption on the system re-activation from power
+	down mode. The stack size must be large enough to hold the return
+	address (4 bytes) and the _AdvIdleCheckSleep() stack frame.
+
 config TICKLESS_IDLE
 	bool
 	prompt "Tickless idle"
 	default y
-	depends on ADVANCED_POWER_MANAGEMENT
+	depends on MICROKERNEL || NANOKERNEL_TICKLESS_IDLE_SUPPORTED
 	help
 	This option suppresses periodic system clock interrupts whenever the
 	kernel becomes idle. This permits the system to remain in a power
 	saving state for extended periods without having to wake up to
 	service each tick as it occurs.
 
+	As a policy, an architecture should always provide support for tickless in
+	the microkernel. If an architecture also provides support for nanokernel
+	systems, it must select the NANOKERNEL_TICKLESS_IDLE_SUPPORTED kconfig
+	option.
+
 config TICKLESS_IDLE_THRESH
 	int
 	prompt "Tickless idle threshold"
 	default 3
 	depends on TICKLESS_IDLE
 	help
-	This option disables clock interrupt suppression when the kernel idles
+	This option enables clock interrupt suppression when the kernel idles
 	for only a short period of time. It specifies the minimum number of
 	ticks that must occur before the next kernel timer expires in order
 	for suppression to happen.
 
+endmenu
+
 if MICROKERNEL
 source "kernel/microkernel/Kconfig"
 endif

kernel/microkernel/Kconfig

@@ -195,44 +195,4 @@ config  THREAD_MONITOR
 	  and fibers (excluding those that have not yet started or have
 	  already terminated).
 
-config ADVANCED_POWER_MANAGEMENT
-	bool
-	prompt "Advanced power management"
-	default n
-	depends on MICROKERNEL
-	help
-	This option enables the platform to implement extra power management
-	policies whenever the kernel becomes idle. The kernel invokes
-	_sys_power_save_idle() to inform the power management subsystem of the
-	number of ticks until the next kernel timer is due to expire.
-
-menu "Advanced Power Management Features"
-	depends on MICROKERNEL && ADVANCED_POWER_MANAGEMENT && ADVANCED_IDLE_SUPPORTED
-
-config  ADVANCED_IDLE
-	bool
-	prompt "Advanced idle state"
-	default n
-	depends on ADVANCED_POWER_MANAGEMENT && ADVANCED_IDLE_SUPPORTED
-	help
-	This option enables the kernel to interface to a custom advanced idle
-	power saving manager. This permits the system to enter a custom
-	power saving state when the kernel becomes idle for extended periods,
-	and then to restore the system to its previous state (rather than
-	booting up from scratch) when the kernel is re-activated.
-
-config ADV_IDLE_STACK_SIZE
-	int
-	prompt "Advanced idle state stack size"
-	default 16
-	depends on ADVANCED_IDLE
-	help
-	This option defines the size of the separate stack used during the
-	system state check while the booting up. A separate stack is used
-	to avoid memory corruption on the system re-activation from power
-	down mode. The stack size must be large enough to hold the return
-	address (4 bytes) and the _AdvIdleCheckSleep() stack frame.
-
-endmenu
-
 endmenu

kernel/nanokernel/Kconfig

@@ -83,6 +83,13 @@ config  NANO_TIMERS
 	Allow fibers and tasks to wait on nanokernel timers, which can be
 	accessed using the nano_timer_xxx() APIs.
 
+config NANOKERNEL_TICKLESS_IDLE_SUPPORTED
+	bool
+	default n
+	help
+	To be selected by an architecture if it does support tickless idle in
+	nanokernel systems.
+
 config ERRNO
 	bool
 	prompt "Enable errno support"
@@ -91,4 +98,5 @@ config ERRNO
 	Enable per-thread errno in the kernel. Application and library code must
 	include errno.h provided by the C library (libc) to use the errno symbol.
 	The C library must access the per-thread errno via the _get_errno() symbol.
+
 endmenu