During MPIPL (aka fadump), OPAL triggers the S0 SBE interrupt to trigger
MPIPL.

Currently S0 interrupt is unimplemented in QEMU.

Implement S0 interrupt as 'pause_vcpus' + 'guest_reset' in QEMU, as the
SBE's implementation of S0 seems to be basically "stop all clocks" and
then "host reset".

pause_vcpus is done in a later patch when register preserving support is
added

See 'stopClocksS0' in SBE source code for more information.

Also log both S0 and S1 interrupts.

Signed-off-by: Aditya Gupta <adityag@linux.ibm.com>
---
 hw/ppc/meson.build         |  1 +
 hw/ppc/pnv_mpipl.c         | 26 ++++++++++++++++++++++++++
 hw/ppc/pnv_sbe.c           | 29 +++++++++++++++++++++++++++++
 include/hw/ppc/pnv.h       |  6 ++++++
 include/hw/ppc/pnv_mpipl.h | 19 +++++++++++++++++++
 5 files changed, 81 insertions(+)
 create mode 100644 hw/ppc/pnv_mpipl.c
 create mode 100644 include/hw/ppc/pnv_mpipl.h

diff --git a/hw/ppc/meson.build b/hw/ppc/meson.build
index f7dac87a2a48..c61fba4ec8f2 100644
--- a/hw/ppc/meson.build
+++ b/hw/ppc/meson.build
@@ -56,6 +56,7 @@ ppc_ss.add(when: 'CONFIG_POWERNV', if_true: files(
   'pnv_pnor.c',
   'pnv_nest_pervasive.c',
   'pnv_n1_chiplet.c',
+  'pnv_mpipl.c',
 ))
 # PowerPC 4xx boards
 ppc_ss.add(when: 'CONFIG_PPC405', if_true: files(
diff --git a/hw/ppc/pnv_mpipl.c b/hw/ppc/pnv_mpipl.c
new file mode 100644
index 000000000000..d8c9b7a428b7
--- /dev/null
+++ b/hw/ppc/pnv_mpipl.c
@@ -0,0 +1,26 @@
+/*
+ * Emulation of MPIPL (Memory Preserving Initial Program Load), aka fadump
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include "qemu/osdep.h"
+#include "system/runstate.h"
+#include "hw/ppc/pnv.h"
+#include "hw/ppc/pnv_mpipl.h"
+
+void do_mpipl_preserve(PnvMachineState *pnv)
+{
+    /* Mark next boot as Memory-preserving boot */
+    pnv->mpipl_state.is_next_boot_mpipl = true;
+
+    /*
+     * Do a guest reset.
+     * Next reset will see 'is_next_boot_mpipl' as true, and trigger MPIPL
+     *
+     * Requirement:
+     * GUEST_RESET is expected to NOT clear the memory, as is the case when
+     * this is merged
+     */
+    qemu_system_reset_request(SHUTDOWN_CAUSE_GUEST_RESET);
+}
diff --git a/hw/ppc/pnv_sbe.c b/hw/ppc/pnv_sbe.c
index b9b28c5deaef..d004b7d5c225 100644
--- a/hw/ppc/pnv_sbe.c
+++ b/hw/ppc/pnv_sbe.c
@@ -21,11 +21,14 @@
 #include "qapi/error.h"
 #include "qemu/log.h"
 #include "qemu/module.h"
+#include "system/cpus.h"
+#include "system/runstate.h"
 #include "hw/irq.h"
 #include "hw/qdev-properties.h"
 #include "hw/ppc/pnv.h"
 #include "hw/ppc/pnv_xscom.h"
 #include "hw/ppc/pnv_sbe.h"
+#include "hw/ppc/pnv_mpipl.h"
 #include "trace.h"
 
 /*
@@ -113,11 +116,37 @@ static uint64_t pnv_sbe_power9_xscom_ctrl_read(void *opaque, hwaddr addr,
 static void pnv_sbe_power9_xscom_ctrl_write(void *opaque, hwaddr addr,
                                        uint64_t val, unsigned size)
 {
+    PnvMachineState *pnv = PNV_MACHINE(qdev_get_machine());
+    PnvSBE *sbe = opaque;
     uint32_t offset = addr >> 3;
 
     trace_pnv_sbe_xscom_ctrl_write(addr, val);
 
     switch (offset) {
+    case SBE_CONTROL_REG_RW:
+        switch (val) {
+        case SBE_CONTROL_REG_S0:
+            qemu_log_mask(LOG_UNIMP, "SBE: S0 Interrupt triggered\n");
+
+            pnv_sbe_set_host_doorbell(sbe, sbe->host_doorbell | SBE_HOST_RESPONSE_MASK);
+
+            /* Preserve memory regions and CPU state, if MPIPL is registered */
+            do_mpipl_preserve(pnv);
+
+            /*
+             * Control may not come back here as 'do_mpipl_preserve' triggers
+             * a guest reboot
+             */
+            break;
+        case SBE_CONTROL_REG_S1:
+            qemu_log_mask(LOG_UNIMP, "SBE: S1 Interrupt triggered\n");
+            break;
+        default:
+            qemu_log_mask(LOG_UNIMP,
+                "SBE: CONTROL_REG_RW: Unknown value: Ox%."
+                  HWADDR_PRIx "\n", val);
+        }
+        break;
     default:
         qemu_log_mask(LOG_UNIMP, "SBE Unimplemented register: Ox%"
                       HWADDR_PRIx "\n", addr >> 3);
diff --git a/include/hw/ppc/pnv.h b/include/hw/ppc/pnv.h
index cbdddfc73cd4..02baa0012460 100644
--- a/include/hw/ppc/pnv.h
+++ b/include/hw/ppc/pnv.h
@@ -25,6 +25,7 @@
 #include "hw/sysbus.h"
 #include "hw/ipmi/ipmi.h"
 #include "hw/ppc/pnv_pnor.h"
+#include "hw/ppc/pnv_mpipl.h"
 
 #define TYPE_PNV_CHIP "pnv-chip"
 
@@ -111,6 +112,8 @@ struct PnvMachineState {
 
     bool         big_core;
     bool         lpar_per_core;
+
+    MpiplPreservedState mpipl_state;
 };
 
 PnvChip *pnv_get_chip(PnvMachineState *pnv, uint32_t chip_id);
@@ -290,4 +293,7 @@ void pnv_bmc_set_pnor(IPMIBmc *bmc, PnvPnor *pnor);
 
 #define PNV11_OCC_SENSOR_BASE(chip) PNV10_OCC_SENSOR_BASE(chip)
 
+/* MPIPL helpers */
+void do_mpipl_preserve(PnvMachineState *pnv);
+
 #endif /* PPC_PNV_H */
diff --git a/include/hw/ppc/pnv_mpipl.h b/include/hw/ppc/pnv_mpipl.h
new file mode 100644
index 000000000000..c544984dc76d
--- /dev/null
+++ b/include/hw/ppc/pnv_mpipl.h
@@ -0,0 +1,19 @@
+/*
+ * Emulation of MPIPL (Memory Preserving Initial Program Load), aka fadump
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#ifndef PNV_MPIPL_H
+#define PNV_MPIPL_H
+
+#include "qemu/osdep.h"
+
+typedef struct MpiplPreservedState MpiplPreservedState;
+
+/* Preserved state to be saved in PnvMachineState */
+struct MpiplPreservedState {
+    bool       is_next_boot_mpipl;
+};
+
+#endif
-- 
2.52.0