MAX78000: TRNG Implementation

This commit implements the True Random Number
Generator for the MAX78000

Signed-off-by: Jackson Donaldson <jcksn@duck.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20250704223239.248781-9-jcksn@duck.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

7 files changed, 186 insertions, 0 deletions

diff --git a/hw/arm/Kconfig b/hw/arm/Kconfig
index a96349e..c7aae4c 100644
--- a/hw/arm/Kconfig
+++ b/hw/arm/Kconfig
@@ -369,6 +369,7 @@ config MAX78000_SOC
     select MAX78000_ICC
     select MAX78000_UART
     select MAX78000_GCR
+    select MAX78000_TRNG
 
 config RASPI
     bool
diff --git a/hw/misc/Kconfig b/hw/misc/Kconfig
index fde2266..dd6a6e5 100644
--- a/hw/misc/Kconfig
+++ b/hw/misc/Kconfig
@@ -53,6 +53,9 @@ config MAX78000_GCR
 config MAX78000_ICC
     bool
 
+config MAX78000_TRNG
+    bool
+
 config MOS6522
     bool
 
diff --git a/hw/misc/max78000_gcr.c b/hw/misc/max78000_gcr.c
index 8c282f3..5916ee6 100644
--- a/hw/misc/max78000_gcr.c
+++ b/hw/misc/max78000_gcr.c
@@ -14,6 +14,7 @@
 #include "migration/vmstate.h"
 #include "hw/qdev-properties.h"
 #include "hw/char/max78000_uart.h"
+#include "hw/misc/max78000_trng.h"
 #include "hw/misc/max78000_gcr.h"
 
 
@@ -157,6 +158,9 @@ static void max78000_gcr_write(void *opaque, hwaddr addr,
         if (val & UART0_RESET) {
             device_cold_reset(s->uart0);
         }
+        if (val & TRNG_RESET) {
+            device_cold_reset(s->trng);
+        }
         /* TODO: As other devices are implemented, add them here */
         break;
 
@@ -257,6 +261,8 @@ static const Property max78000_gcr_properties[] = {
                      TYPE_MAX78000_UART, DeviceState*),
     DEFINE_PROP_LINK("uart2", Max78000GcrState, uart2,
                      TYPE_MAX78000_UART, DeviceState*),
+    DEFINE_PROP_LINK("trng", Max78000GcrState, trng,
+                        TYPE_MAX78000_TRNG, DeviceState*),
 };
 
 static const MemoryRegionOps max78000_gcr_ops = {
diff --git a/hw/misc/max78000_trng.c b/hw/misc/max78000_trng.c
new file mode 100644
index 0000000..ecdaef5
--- /dev/null
+++ b/hw/misc/max78000_trng.c
@@ -0,0 +1,139 @@
+/*
+ * MAX78000 True Random Number Generator
+ *
+ * Copyright (c) 2025 Jackson Donaldson <jcksn@duck.com>
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include "qemu/osdep.h"
+#include "qemu/log.h"
+#include "trace.h"
+#include "hw/irq.h"
+#include "migration/vmstate.h"
+#include "hw/misc/max78000_trng.h"
+#include "qemu/guest-random.h"
+
+static uint64_t max78000_trng_read(void *opaque, hwaddr addr,
+                                    unsigned int size)
+{
+    uint32_t data;
+
+    Max78000TrngState *s = opaque;
+    switch (addr) {
+    case CTRL:
+        return s->ctrl;
+
+    case STATUS:
+        return 1;
+
+    case DATA:
+        /*
+         * When interrupts are enabled, reading random data should cause a
+         * new interrupt to be generated; since there's always a random number
+         * available, we could qemu_set_irq(s->irq, s->ctrl & RND_IE). Because
+         * of how trng_write is set up, this is always a noop, so don't
+         */
+        qemu_guest_getrandom_nofail(&data, sizeof(data));
+        return data;
+
+    default:
+        qemu_log_mask(LOG_GUEST_ERROR, "%s: Bad offset 0x%"
+            HWADDR_PRIx "\n", __func__, addr);
+        break;
+    }
+    return 0;
+}
+
+static void max78000_trng_write(void *opaque, hwaddr addr,
+                    uint64_t val64, unsigned int size)
+{
+    Max78000TrngState *s = opaque;
+    uint32_t val = val64;
+    switch (addr) {
+    case CTRL:
+        /* TODO: implement AES keygen */
+        s->ctrl = val;
+
+        /*
+         * This device models random number generation as taking 0 time.
+         * A new random number is always available, so the condition for the
+         * RND interrupt is always fulfilled; we can just set irq to 1.
+         */
+        if (val & RND_IE) {
+            qemu_set_irq(s->irq, 1);
+        } else{
+            qemu_set_irq(s->irq, 0);
+        }
+        break;
+
+    default:
+        qemu_log_mask(LOG_GUEST_ERROR, "%s: Bad offset 0x%"
+            HWADDR_PRIx "\n", __func__, addr);
+        break;
+    }
+}
+
+static void max78000_trng_reset_hold(Object *obj, ResetType type)
+{
+    Max78000TrngState *s = MAX78000_TRNG(obj);
+    s->ctrl = 0;
+    s->status = 0;
+    s->data = 0;
+}
+
+static const MemoryRegionOps max78000_trng_ops = {
+    .read = max78000_trng_read,
+    .write = max78000_trng_write,
+    .endianness = DEVICE_LITTLE_ENDIAN,
+    .valid.min_access_size = 4,
+    .valid.max_access_size = 4,
+};
+
+static const VMStateDescription max78000_trng_vmstate = {
+    .name = TYPE_MAX78000_TRNG,
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .fields = (const VMStateField[]) {
+        VMSTATE_UINT32(ctrl, Max78000TrngState),
+        VMSTATE_UINT32(status, Max78000TrngState),
+        VMSTATE_UINT32(data, Max78000TrngState),
+        VMSTATE_END_OF_LIST()
+    }
+};
+
+static void max78000_trng_init(Object *obj)
+{
+    Max78000TrngState *s = MAX78000_TRNG(obj);
+    sysbus_init_irq(SYS_BUS_DEVICE(obj), &s->irq);
+
+    memory_region_init_io(&s->mmio, obj, &max78000_trng_ops, s,
+                        TYPE_MAX78000_TRNG, 0x1000);
+    sysbus_init_mmio(SYS_BUS_DEVICE(obj), &s->mmio);
+
+}
+
+static void max78000_trng_class_init(ObjectClass *klass, const void *data)
+{
+    ResettableClass *rc = RESETTABLE_CLASS(klass);
+    DeviceClass *dc = DEVICE_CLASS(klass);
+
+    rc->phases.hold = max78000_trng_reset_hold;
+    dc->vmsd = &max78000_trng_vmstate;
+
+}
+
+static const TypeInfo max78000_trng_info = {
+    .name          = TYPE_MAX78000_TRNG,
+    .parent        = TYPE_SYS_BUS_DEVICE,
+    .instance_size = sizeof(Max78000TrngState),
+    .instance_init = max78000_trng_init,
+    .class_init    = max78000_trng_class_init,
+};
+
+static void max78000_trng_register_types(void)
+{
+    type_register_static(&max78000_trng_info);
+}
+
+type_init(max78000_trng_register_types)
diff --git a/hw/misc/meson.build b/hw/misc/meson.build
index 283d06d..c7c57d9 100644
--- a/hw/misc/meson.build
+++ b/hw/misc/meson.build
@@ -72,6 +72,7 @@ system_ss.add(when: 'CONFIG_IMX', if_true: files(
 ))
 system_ss.add(when: 'CONFIG_MAX78000_GCR', if_true: files('max78000_gcr.c'))
 system_ss.add(when: 'CONFIG_MAX78000_ICC', if_true: files('max78000_icc.c'))
+system_ss.add(when: 'CONFIG_MAX78000_TRNG', if_true: files('max78000_trng.c'))
 system_ss.add(when: 'CONFIG_NPCM7XX', if_true: files(
   'npcm_clk.c',
   'npcm_gcr.c',
diff --git a/include/hw/misc/max78000_gcr.h b/include/hw/misc/max78000_gcr.h
index f04c8a3..23ddf08 100644
--- a/include/hw/misc/max78000_gcr.h
+++ b/include/hw/misc/max78000_gcr.h
@@ -123,6 +123,7 @@ struct Max78000GcrState {
     DeviceState *uart0;
     DeviceState *uart1;
     DeviceState *uart2;
+    DeviceState *trng;
 
 };
 
diff --git a/include/hw/misc/max78000_trng.h b/include/hw/misc/max78000_trng.h
new file mode 100644
index 0000000..c5a8129
--- /dev/null
+++ b/include/hw/misc/max78000_trng.h
@@ -0,0 +1,35 @@
+/*
+ * MAX78000 True Random Number Generator
+ *
+ * Copyright (c) 2025 Jackson Donaldson <jcksn@duck.com>
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+#ifndef HW_MAX78000_TRNG_H
+#define HW_MAX78000_TRNG_H
+
+#include "hw/sysbus.h"
+#include "qom/object.h"
+
+#define TYPE_MAX78000_TRNG "max78000-trng"
+OBJECT_DECLARE_SIMPLE_TYPE(Max78000TrngState, MAX78000_TRNG)
+
+#define CTRL 0
+#define STATUS 4
+#define DATA 8
+
+#define RND_IE (1 << 1)
+
+struct Max78000TrngState {
+    SysBusDevice parent_obj;
+
+    MemoryRegion mmio;
+
+    uint32_t ctrl;
+    uint32_t status;
+    uint32_t data;
+
+    qemu_irq irq;
+};
+
+#endif