[ot] hw/opentitan: ot_rstmgr: add a debug property to shutdown the VM on reset

Signed-off-by: Emmanuel Blot <eblot@rivosinc.com>

Author: rivos-eblot

docs/opentitan/darjeeling.md

@@ -135,7 +135,8 @@ See [`tools.md`](tools.md)
   is set to 10 MHz. This option is very useful/mandatory to run many OpenTitan tests that rely on
   time or CPU cycle to validate features. Using `-icount` option slows down execution speed though,
   so it is not recommended to use it when the main goal is to develop SW to run on the virtual
-  machine.
+  machine. An alternative is to use `-icount shift=auto`, which offers fatest emulation execution,
+  while preserving an accurate ratio between the vCPU clock and the virtual devices.
 
 * `no_epmp_cfg=true` can be appended to the machine option switch, _i.e._
   `-M ot-darjeeeling,no_epmp_cfg=true` to disable the initial ePMP configuration, which can be very
@@ -162,6 +163,10 @@ See [`tools.md`](tools.md)
 * `-cpu lowrisc-ibex,x-zbr=false` can be used to force disable the Zbr experimental-and-deprecated
   RISC-V bitmap extension for CRC32 extension.
 
+* `-global ot-rstmgr.fatal_reset=N`, where `N` is an unsigned integer. Force QEMU VM to exit the
+  N^th^ time the reset manager received a reset request, rather than rebooting the whole machine as
+  the default behavior.
+
 ### AES
 
 * `-global ot-aes.fast-mode=false` can be used to better emulate AES HW IP, as some OT tests expect

hw/opentitan/ot_rstmgr.c

@@ -44,6 +44,7 @@
 #include "hw/riscv/ibex_irq.h"
 #include "hw/sysbus.h"
 #include "sysemu/hw_accel.h"
+#include "sysemu/runstate.h"
 #include "trace.h"
 
 
@@ -154,6 +155,7 @@ struct OtRstMgrState {
     uint32_t *regs;
 
     char *ot_id;
+    uint32_t fatal_reset;
     bool por; /* Power-On Reset property */
 };
 
@@ -381,6 +383,14 @@ static void ot_rstmgr_regs_write(void *opaque, hwaddr addr, uint64_t val64,
              * hardware."
              */
             ibex_irq_set(&s->sw_reset, (int)true);
+            if (s->fatal_reset) {
+                s->fatal_reset--;
+                if (!s->fatal_reset) {
+                    error_report("fatal reset triggered");
+                    qemu_system_shutdown_request_with_code(
+                        SHUTDOWN_CAUSE_GUEST_SHUTDOWN, 1);
+                }
+            }
         }
         break;
     case R_RESET_INFO:
@@ -469,6 +479,7 @@ static void ot_rstmgr_regs_write(void *opaque, hwaddr addr, uint64_t val64,
 
 static Property ot_rstmgr_properties[] = {
     DEFINE_PROP_STRING("ot_id", OtRstMgrState, ot_id),
+    DEFINE_PROP_UINT32("fatal_reset", OtRstMgrState, fatal_reset, 0),
     /* this property is only used to store initial reset reason state */
     DEFINE_PROP_BOOL("por", OtRstMgrState, por, true),
     DEFINE_PROP_END_OF_LIST(),