riscv: add SBI system reset extension

The System Reset extension provides functions to shutdown or reboot the
system via SBI firmware. This newly defined extension supersedes the
functionality of the legacy shutdown extension.

Update the SBI code to use the new System Reset extension when
available, and fall back to the legacy one.

Reviewed By:	kp, jhb
MFC after:	3 days
Differential Revision:	https://reviews.freebsd.org/D28226

3 files changed, 39 insertions, 11 deletions

diff --git a/sys/riscv/include/sbi.h b/sys/riscv/include/sbi.h
index 50cacb3e6e5a..9d3f4076dcb2 100644
--- a/sys/riscv/include/sbi.h
+++ b/sys/riscv/include/sbi.h
@@ -99,6 +99,15 @@
 #define	 SBI_HSM_STATUS_START_PENDING	2
 #define	 SBI_HSM_STATUS_STOP_PENDING	3
 
+/* System Reset (SRST) Extension */
+#define	SBI_EXT_ID_SRST			0x53525354
+#define	SBI_SRST_SYSTEM_RESET		0
+#define	 SBI_SRST_TYPE_SHUTDOWN		0
+#define	 SBI_SRST_TYPE_COLD_REBOOT	1
+#define	 SBI_SRST_TYPE_WARM_REBOOT	2
+#define	 SBI_SRST_REASON_NONE		0
+#define	 SBI_SRST_REASON_SYSTEM_FAILURE	1
+
 /* Legacy Extensions */
 #define	SBI_SET_TIMER			0
 #define	SBI_CONSOLE_PUTCHAR		1
@@ -199,6 +208,18 @@ void sbi_hsm_hart_stop(void);
  */
 int sbi_hsm_hart_status(u_long hart);
 
+/* System Reset extension functions. */
+
+/*
+ * Reset the system based on the following 'type' and 'reason' chosen from:
+ *  - SBI_SRST_TYPE_SHUTDOWN
+ *  - SBI_SRST_TYPE_COLD_REBOOT
+ *  - SBI_SRST_TYPE_WARM_REBOOT
+ *  - SBI_SRST_REASON_NONE
+ *  - SBI_SRST_REASON_SYSTEM_FAILURE
+ */
+void sbi_system_reset(u_long reset_type, u_long reset_reason);
+
 /* Legacy extension functions. */
 static __inline void
 sbi_console_putchar(int ch)
@@ -218,13 +239,6 @@ sbi_console_getchar(void)
 	return (SBI_CALL0(SBI_CONSOLE_GETCHAR, 0).error);
 }
 
-static __inline void
-sbi_shutdown(void)
-{
-
-	(void)SBI_CALL0(SBI_SHUTDOWN, 0);
-}
-
 void sbi_print_version(void);
 void sbi_init(void);
 
diff --git a/sys/riscv/riscv/sbi.c b/sys/riscv/riscv/sbi.c
index a7688b13f283..6897fce9cad3 100644
--- a/sys/riscv/riscv/sbi.c
+++ b/sys/riscv/riscv/sbi.c
@@ -49,6 +49,7 @@ u_long sbi_impl_version;
 static bool has_time_extension = false;
 static bool has_ipi_extension = false;
 static bool has_rfnc_extension = false;
+static bool has_srst_extension = false;
 
 static struct sbi_ret
 sbi_get_spec_version(void)
@@ -90,7 +91,18 @@ static void
 sbi_shutdown_final(void *dummy __unused, int howto)
 {
 	if ((howto & RB_POWEROFF) != 0)
-		sbi_shutdown();
+		sbi_system_reset(SBI_SRST_TYPE_SHUTDOWN, SBI_SRST_REASON_NONE);
+}
+
+void
+sbi_system_reset(u_long reset_type, u_long reset_reason)
+{
+	/* Use the SRST extension, if available. */
+	if (has_srst_extension) {
+		(void)SBI_CALL2(SBI_EXT_ID_SRST, SBI_SRST_SYSTEM_RESET,
+		    reset_type, reset_reason);
+	}
+	(void)SBI_CALL0(SBI_SHUTDOWN, 0);
 }
 
 void
@@ -277,6 +289,8 @@ sbi_init(void)
 		has_ipi_extension = true;
 	if (sbi_probe_extension(SBI_EXT_ID_RFNC) != 0)
 		has_rfnc_extension = true;
+	if (sbi_probe_extension(SBI_EXT_ID_SRST) != 0)
+		has_srst_extension = true;
 
 	/*
 	 * Probe for legacy extensions. We still rely on many of them to be
@@ -299,8 +313,8 @@ sbi_init(void)
 	KASSERT(has_rfnc_extension ||
 	    sbi_probe_extension(SBI_REMOTE_SFENCE_VMA_ASID) != 0,
 	    ("SBI doesn't implement sbi_remote_sfence_vma_asid()"));
-	KASSERT(sbi_probe_extension(SBI_SHUTDOWN) != 0,
-	    ("SBI doesn't implement sbi_shutdown()"));
+	KASSERT(has_srst_extension || sbi_probe_extension(SBI_SHUTDOWN) != 0,
+	    ("SBI doesn't implement a shutdown or reset extension"));
 }
 
 static void
diff --git a/sys/riscv/riscv/vm_machdep.c b/sys/riscv/riscv/vm_machdep.c
index f38f1c04caa8..094662413f4e 100644
--- a/sys/riscv/riscv/vm_machdep.c
+++ b/sys/riscv/riscv/vm_machdep.c
@@ -110,7 +110,7 @@ void
 cpu_reset(void)
 {
 
-	sbi_shutdown();
+	sbi_system_reset(SBI_SRST_TYPE_COLD_REBOOT, SBI_SRST_REASON_NONE);
 
 	while(1);
 }