diff --git a/include/hw/fsi/fsi.h b/include/hw/fsi/fsi.h
index 50e8f5c888f1..e00f6ef078c8 100644
--- a/include/hw/fsi/fsi.h
+++ b/include/hw/fsi/fsi.h
@@ -7,7 +7,13 @@
 #ifndef FSI_FSI_H
 #define FSI_FSI_H
 
+#include "exec/memory.h"
 #include "hw/qdev-core.h"
+#include "hw/fsi/lbus.h"
+#include "qemu/bitops.h"
+
+/* Bitwise operations at the word level. */
+#define BE_GENMASK(hb, lb)  MAKE_64BIT_MASK((lb), ((hb) - (lb) + 1))
 
 #define TYPE_FSI_BUS "fsi.bus"
 OBJECT_DECLARE_SIMPLE_TYPE(FSIBus, FSI_BUS)
@@ -16,4 +22,16 @@ typedef struct FSIBus {
     BusState bus;
 } FSIBus;
 
+#define TYPE_FSI_SLAVE "fsi.slave"
+OBJECT_DECLARE_SIMPLE_TYPE(FSISlaveState, FSI_SLAVE)
+
+#define FSI_SLAVE_CONTROL_NR_REGS ((0x40 >> 2) + 1)
+
+typedef struct FSISlaveState {
+    DeviceState parent;
+
+    MemoryRegion iomem;
+    uint32_t regs[FSI_SLAVE_CONTROL_NR_REGS];
+} FSISlaveState;
+
 #endif /* FSI_FSI_H */
diff --git a/hw/fsi/fsi.c b/hw/fsi/fsi.c
index 60cb03f7a24e..9a5f4e616f16 100644
--- a/hw/fsi/fsi.c
+++ b/hw/fsi/fsi.c
@@ -5,18 +5,98 @@
  * IBM Flexible Service Interface
  */
 #include "qemu/osdep.h"
+#include "qapi/error.h"
+#include "qemu/log.h"
+#include "trace.h"
 
 #include "hw/fsi/fsi.h"
 
+#define TO_REG(x)                               ((x) >> 2)
+
 static const TypeInfo fsi_bus_info = {
     .name = TYPE_FSI_BUS,
     .parent = TYPE_BUS,
     .instance_size = sizeof(FSIBus),
 };
 
-static void fsi_bus_register_types(void)
+static uint64_t fsi_slave_read(void *opaque, hwaddr addr, unsigned size)
+{
+    FSISlaveState *s = FSI_SLAVE(opaque);
+    int reg = TO_REG(addr);
+
+    trace_fsi_slave_read(addr, size);
+
+    if (reg >= FSI_SLAVE_CONTROL_NR_REGS) {
+        qemu_log_mask(LOG_GUEST_ERROR,
+                      "%s: Out of bounds read: 0x%"HWADDR_PRIx" for %u\n",
+                      __func__, addr, size);
+        return 0;
+    }
+
+    return s->regs[reg];
+}
+
+static void fsi_slave_write(void *opaque, hwaddr addr, uint64_t data,
+                                 unsigned size)
+{
+    FSISlaveState *s = FSI_SLAVE(opaque);
+    int reg = TO_REG(addr);
+
+    trace_fsi_slave_write(addr, size, data);
+
+    if (reg >= FSI_SLAVE_CONTROL_NR_REGS) {
+        qemu_log_mask(LOG_GUEST_ERROR,
+                      "%s: Out of bounds write: 0x%"HWADDR_PRIx" for %u\n",
+                      __func__, addr, size);
+        return;
+    }
+
+    s->regs[reg] = data;
+}
+
+static const struct MemoryRegionOps fsi_slave_ops = {
+    .read = fsi_slave_read,
+    .write = fsi_slave_write,
+    .endianness = DEVICE_BIG_ENDIAN,
+};
+
+static void fsi_slave_reset(DeviceState *dev)
+{
+    FSISlaveState *s = FSI_SLAVE(dev);
+
+    /* Initialize registers */
+    memset(s->regs, 0, sizeof(s->regs));
+}
+
+static void fsi_slave_init(Object *o)
+{
+    FSISlaveState *s = FSI_SLAVE(o);
+
+    memory_region_init_io(&s->iomem, OBJECT(s), &fsi_slave_ops,
+                          s, TYPE_FSI_SLAVE, 0x400);
+}
+
+static void fsi_slave_class_init(ObjectClass *klass, void *data)
+{
+    DeviceClass *dc = DEVICE_CLASS(klass);
+
+    dc->bus_type = TYPE_FSI_BUS;
+    dc->desc = "FSI Slave";
+    dc->reset = fsi_slave_reset;
+}
+
+static const TypeInfo fsi_slave_info = {
+    .name = TYPE_FSI_SLAVE,
+    .parent = TYPE_DEVICE,
+    .instance_init = fsi_slave_init,
+    .instance_size = sizeof(FSISlaveState),
+    .class_init = fsi_slave_class_init,
+};
+
+static void fsi_register_types(void)
 {
     type_register_static(&fsi_bus_info);
+    type_register_static(&fsi_slave_info);
 }
 
-type_init(fsi_bus_register_types);
+type_init(fsi_register_types);
diff --git a/hw/fsi/trace-events b/hw/fsi/trace-events
index c5753e27910a..8f29adb7df92 100644
--- a/hw/fsi/trace-events
+++ b/hw/fsi/trace-events
@@ -1,2 +1,4 @@
 fsi_scratchpad_read(uint64_t addr, uint32_t size) "@0x%" PRIx64 " size=%d"
 fsi_scratchpad_write(uint64_t addr, uint32_t size, uint64_t data) "@0x%" PRIx64 " size=%d value=0x%"PRIx64
+fsi_slave_read(uint64_t addr, uint32_t size) "@0x%" PRIx64 " size=%d"
+fsi_slave_write(uint64_t addr, uint32_t size, uint64_t data) "@0x%" PRIx64 " size=%d value=0x%"PRIx64
