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>

1 files changed, 139 insertions, 0 deletions

diff --git a/hw/misc/max78000_trng.c b/hw/misc/max78000_trng.c
new file mode 100644
index 0000000000..ecdaef53b6
--- /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)