cpuidle: Add RISC-V SBI CPU idle driver

The RISC-V SBI HSM extension provides HSM suspend call which can
be used by Linux RISC-V to enter platform specific low-power state.

This patch adds a CPU idle driver based on RISC-V SBI calls which
will populate idle states from device tree and use SBI calls to
entry these idle states.

Signed-off-by: Anup Patel <anup.patel@wdc.com>

MAINTAINERS

@@ -4641,6 +4641,13 @@ S:	Supported
 F:	drivers/cpuidle/cpuidle-psci.h
 F:	drivers/cpuidle/cpuidle-psci-domain.c
 
+CPUIDLE DRIVER - RISC-V SBI
+M:	Anup Patel <anup.patel@wdc.com>
+L:	linux-pm@vger.kernel.org
+L:	linux-riscv@lists.infradead.org
+S:	Supported
+F:	drivers/cpuidle/cpuidle-sbi.c
+
 CRAMFS FILESYSTEM
 M:	Nicolas Pitre <nico@fluxnic.net>
 S:	Maintained

drivers/cpuidle/Kconfig

@@ -66,6 +66,11 @@ depends on PPC
 source "drivers/cpuidle/Kconfig.powerpc"
 endmenu
 
+menu "RISC-V CPU Idle Drivers"
+depends on RISCV
+source "drivers/cpuidle/Kconfig.riscv"
+endmenu
+
 config HALTPOLL_CPUIDLE
 	tristate "Halt poll cpuidle driver"
 	depends on X86 && KVM_GUEST

drivers/cpuidle/Kconfig.riscv

@@ -0,0 +1,24 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# RISC-V CPU Idle drivers
+#
+
+config RISCV_SBI_CPUIDLE
+	bool "RISC-V SBI CPU idle Driver"
+	depends on RISCV_SBI
+	select DT_IDLE_STATES
+	select CPU_IDLE_MULTIPLE_DRIVERS
+	help
+	  Select this option to enable RISC-V SBI firmware based CPU idle
+	  driver for RISC-V systems.
+
+config RISCV_SBI_CPUIDLE_DOMAIN
+	bool "RISC-V SBI CPU idle Domain"
+	depends on RISCV_SBI_CPUIDLE
+	depends on PM_GENERIC_DOMAINS_OF
+	select DT_IDLE_GENPD
+	default y
+	help
+	  Select this to enable the RISC-V SBI based CPU idle driver to use
+	  PM domains, which is needed to support the hierarchical DT based
+	  layout of the idle states.

drivers/cpuidle/Makefile

@@ -35,3 +35,7 @@ obj-$(CONFIG_MIPS_CPS_CPUIDLE)		+= cpuidle-cps.o
 # POWERPC drivers
 obj-$(CONFIG_PSERIES_CPUIDLE)		+= cpuidle-pseries.o
 obj-$(CONFIG_POWERNV_CPUIDLE)		+= cpuidle-powernv.o
+
+###############################################################################
+# RISC-V drivers
+obj-$(CONFIG_RISCV_SBI_CPUIDLE)		+= cpuidle-sbi.o