[PATCH 8/9] arm64: support cpuidle-haltpoll

[Ankur Arora <ankur.a.arora@oracle.com>]

Add architectural support for the cpuidle-haltpoll driver by defining
arch_haltpoll_*(). Also select ARCH_HAS_OPTIMIZED_POLL since we have
an optimized polling mechanism via smp_cond_load*().

Add the configuration option, ARCH_CPUIDLE_HALTPOLL to allow
cpuidle-haltpoll to be selected.

Note that we limit cpuidle-haltpoll support to when the event-stream is
available. This is necessary because polling via smp_cond_load_relaxed()
uses WFE to wait for a store which might not happen for an prolonged
period of time. So, ensure the event-stream is around to provide a
terminating condition.

Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
 arch/arm64/Kconfig                        | 10 ++++++++++
 arch/arm64/include/asm/cpuidle_haltpoll.h | 21 +++++++++++++++++++++
 2 files changed, 31 insertions(+)
 create mode 100644 arch/arm64/include/asm/cpuidle_haltpoll.h

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 7b11c98b3e84..6f2df162b10e 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -34,6 +34,7 @@ config ARM64
 	select ARCH_HAS_MEMBARRIER_SYNC_CORE
 	select ARCH_HAS_NMI_SAFE_THIS_CPU_OPS
 	select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
+	select ARCH_HAS_OPTIMIZED_POLL
 	select ARCH_HAS_PTE_DEVMAP
 	select ARCH_HAS_PTE_SPECIAL
 	select ARCH_HAS_HW_PTE_YOUNG
@@ -2331,6 +2332,15 @@ config ARCH_HIBERNATION_HEADER
 config ARCH_SUSPEND_POSSIBLE
 	def_bool y
 
+config ARCH_CPUIDLE_HALTPOLL
+	bool "Enable selection of the cpuidle-haltpoll driver"
+	default n
+	help
+	  cpuidle-haltpoll allows for adaptive polling based on
+	  current load before entering the idle state.
+
+	  Some virtualized workloads benefit from using it.
+
 endmenu # "Power management options"
 
 menu "CPU Power Management"
diff --git a/arch/arm64/include/asm/cpuidle_haltpoll.h b/arch/arm64/include/asm/cpuidle_haltpoll.h
new file mode 100644
index 000000000000..a79bdec7f516
--- /dev/null
+++ b/arch/arm64/include/asm/cpuidle_haltpoll.h
@@ -0,0 +1,21 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_HALTPOLL_H
+#define _ASM_HALTPOLL_H
+
+static inline void arch_haltpoll_enable(unsigned int cpu)
+{
+}
+
+static inline void arch_haltpoll_disable(unsigned int cpu)
+{
+}
+
+static inline bool arch_haltpoll_supported(void)
+{
+	/*
+	 * Ensure the event stream is available to provide a terminating
+	 * condition to the WFE in the poll loop.
+	 */
+	return arch_timer_evtstrm_available();
+}
+#endif
-- 
2.39.3