[RFC PATCH] RISC-V: Use SBI SRST extension when available

[Anup Patel]

The SBI SRST extension provides a standard way to poweroff and
reboot the system irrespective to whether Linux RISC-V S-mode
is running natively (HS-mode) or inside Guest/VM (VS-mode).

The draft specification of SBI SRST extension is available in
srbt_v1 branch of: https://github.com/avpatel/riscv-sbi-doc.

This patch extends Linux RISC-V SBI implementation to detect
and use SBI SRST extension.

Signed-off-by: Anup Patel <anup.patel@xxxxxxx>
---
 arch/riscv/include/asm/sbi.h |  7 +++++++
 arch/riscv/kernel/sbi.c      | 25 +++++++++++++++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/arch/riscv/include/asm/sbi.h b/arch/riscv/include/asm/sbi.h
index 653edb25d495..2fcecec7dd0c 100644
--- a/arch/riscv/include/asm/sbi.h
+++ b/arch/riscv/include/asm/sbi.h
@@ -27,6 +27,7 @@ enum sbi_ext_id {
 	SBI_EXT_IPI = 0x735049,
 	SBI_EXT_RFENCE = 0x52464E43,
 	SBI_EXT_HSM = 0x48534D,
+	SBI_EXT_SRST = 0x53525354,
 };
 
 enum sbi_ext_base_fid {
@@ -70,6 +71,12 @@ enum sbi_hsm_hart_status {
 	SBI_HSM_HART_STATUS_STOP_PENDING,
 };
 
+enum sbi_ext_srst_fid {
+	SBI_EXT_SRST_SHUTDOWN = 0,
+	SBI_EXT_SRST_COLD_REBOOT,
+	SBI_EXT_SRST_WARM_REBOOT
+};
+
 #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 226ccce0f9e0..865e028a9a4b 100644
--- a/arch/riscv/kernel/sbi.c
+++ b/arch/riscv/kernel/sbi.c
@@ -7,6 +7,7 @@
 
 #include <linux/init.h>
 #include <linux/pm.h>
+#include <linux/reboot.h>
 #include <asm/sbi.h>
 #include <asm/smp.h>
 
@@ -501,6 +502,23 @@ int sbi_remote_hfence_vvma_asid(const unsigned long *hart_mask,
 }
 EXPORT_SYMBOL(sbi_remote_hfence_vvma_asid);
 
+static int sbi_srst_reboot(struct notifier_block *this,
+			   unsigned long mode, void *cmd)
+{
+	sbi_ecall(SBI_EXT_SRST, (mode == REBOOT_WARM || mode == REBOOT_SOFT) ?
+		  SBI_EXT_SRST_WARM_REBOOT : SBI_EXT_SRST_COLD_REBOOT,
+		  0, 0, 0, 0, 0, 0);
+
+	return NOTIFY_DONE;
+}
+
+static struct notifier_block sbi_srst_reboot_nb;
+
+static void sbi_srst_power_off(void)
+{
+	sbi_ecall(SBI_EXT_SRST, SBI_EXT_SRST_SHUTDOWN, 0, 0, 0, 0, 0, 0);
+}
+
 /**
  * sbi_probe_extension() - Check if an SBI extension ID is supported or not.
  * @extid: The extension ID to be probed.
@@ -593,6 +611,13 @@ int __init sbi_init(void)
 		} else {
 			__sbi_rfence	= __sbi_rfence_v01;
 		}
+		if (sbi_probe_extension(SBI_EXT_SRST) > 0) {
+			pr_info("SBI v0.2 SRST extension detected\n");
+			pm_power_off = sbi_srst_power_off;
+			sbi_srst_reboot_nb.notifier_call = sbi_srst_reboot;
+			sbi_srst_reboot_nb.priority = 192;
+			register_restart_handler(&sbi_srst_reboot_nb);
+		}
 	} else {
 		__sbi_set_timer = __sbi_set_timer_v01;
 		__sbi_send_ipi	= __sbi_send_ipi_v01;
-- 
2.25.1