riscv: add SBI SUSP extension support

RISC-V SBI spec 2.0 [1] introduces System Suspend Extension which can be
used to suspend the platform via SBI firmware.

This patch can be tested on Qemu with recent OpenSBI with
`system-suspend-test` enabled like [2] in DTB.

[1] https://github.com/riscv-non-isa/riscv-sbi-doc/blob/maste...
[2] https://github.com/woodyzhang666/qemu/commit/e4a5120133c1...

Signed-off-by: Woody Zhang <woodylab@foxmail.com>
---
 arch/riscv/include/asm/sbi.h | 10 ++++++++++
 arch/riscv/kernel/sbi.c      | 26 ++++++++++++++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/arch/riscv/include/asm/sbi.h b/arch/riscv/include/asm/sbi.h
index 5b4a1bf5f439..3b04016da671 100644
--- a/arch/riscv/include/asm/sbi.h
+++ b/arch/riscv/include/asm/sbi.h
@@ -30,6 +30,7 @@ enum sbi_ext_id {
 	SBI_EXT_HSM = 0x48534D,
 	SBI_EXT_SRST = 0x53525354,
 	SBI_EXT_PMU = 0x504D55,
+	SBI_EXT_SUSP = 0x53555350,
 
 	/* Experimentals extensions must lie within this range */
 	SBI_EXT_EXPERIMENTAL_START = 0x08000000,
@@ -236,6 +237,15 @@ enum sbi_pmu_ctr_type {
 /* Flags defined for counter stop function */
 #define SBI_PMU_STOP_FLAG_RESET (1 << 0)
 
+enum sbi_ext_susp_fid {
+	SBI_EXT_SUSP_SYSTEM_SUSPEND = 0,
+};
+
+/* SBI suspend sleep types */
+enum sbi_susp_sleep_type {
+	SBI_SUSP_SLEEP_TYPE_SUSPEND = 0x0,
+};
+
 #define SBI_SPEC_VERSION_DEFAULT	0x1
 #define SBI_SPEC_VERSION_MAJOR_SHIFT	24
 #define SBI_SPEC_VERSION_MAJOR_MASK	0x7f
diff --git a/arch/riscv/kernel/sbi.c b/arch/riscv/kernel/sbi.c
index c672c8ba9a2a..9a68959f9f18 100644
--- a/arch/riscv/kernel/sbi.c
+++ b/arch/riscv/kernel/sbi.c
@@ -9,8 +9,10 @@
 #include <linux/init.h>
 #include <linux/pm.h>
 #include <linux/reboot.h>
+#include <linux/suspend.h>
 #include <asm/sbi.h>
 #include <asm/smp.h>
+#include <asm/suspend.h>
 
 /* default SBI version is 0.1 */
 unsigned long sbi_spec_version __ro_after_init = SBI_SPEC_VERSION_DEFAULT;
@@ -520,6 +522,26 @@ static void sbi_srst_power_off(void)
 		       SBI_SRST_RESET_REASON_NONE);
 }
 
+static int sbi_system_suspend(unsigned long arg,
+		unsigned long resume_entry, unsigned long context)
+{
+	struct sbiret ret = {0};
+
+	ret = sbi_ecall(SBI_EXT_SUSP, SBI_EXT_SUSP_SYSTEM_SUSPEND,
+			SBI_SUSP_SLEEP_TYPE_SUSPEND, resume_entry, context, 0, 0, 0);
+	return ret.error;
+}
+
+static int sbi_system_suspend_enter(suspend_state_t state)
+{
+	return cpu_suspend(0, sbi_system_suspend);
+}
+
+static const struct platform_suspend_ops sbi_suspend_ops = {
+	.valid          = suspend_valid_only_mem,
+	.enter          = sbi_system_suspend_enter,
+};
+
 /**
  * sbi_probe_extension() - Check if an SBI extension ID is supported or not.
  * @extid: The extension ID to be probed.
@@ -624,6 +646,10 @@ void __init sbi_init(void)
 			sbi_srst_reboot_nb.priority = 192;
 			register_restart_handler(&sbi_srst_reboot_nb);
 		}
+		if (sbi_probe_extension(SBI_EXT_SUSP)) {
+			pr_info("SBI SUSP extension detected\n");
+			suspend_set_ops(&sbi_suspend_ops);
+		}
 	} else {
 		__sbi_set_timer = __sbi_set_timer_v01;
 		__sbi_send_ipi	= __sbi_send_ipi_v01;
-- 
2.39.2