target-arm: Implement BCM2835 hardware RNG

Recent vanilla Raspberry Pi kernels started to make use of
the hardware random number generator in BCM2835 SoC. As a
result, those kernels wouldn't work anymore under QEMU
but rather just freeze during the boot process.

This patch implements a trivial BCM2835 compatible RNG,
and adds it as a peripheral to BCM2835 platform, which
allows to boot a vanilla Raspberry Pi kernel under Qemu.

Changes since v1:
 * Prevented guest from writing [31..20] bits in rng_status
 * Removed redundant minimum_version_id_old
 * Added field entries for the state
 * Changed realize function to reset

Signed-off-by: Marcin Chojnacki <marcinch7@gmail.com>
Message-id: 20170210210857.47893-1-marcinch7@gmail.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 124 insertions, 0 deletions

diff --git a/hw/misc/bcm2835_rng.c b/hw/misc/bcm2835_rng.c
new file mode 100644
index 0000000000..2242bc5eb5
--- /dev/null
+++ b/hw/misc/bcm2835_rng.c
@@ -0,0 +1,124 @@
+/*
+ * BCM2835 Random Number Generator emulation
+ *
+ * Copyright (C) 2017 Marcin Chojnacki <marcinch7@gmail.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+#include "qemu/osdep.h"
+#include "qemu/log.h"
+#include "hw/misc/bcm2835_rng.h"
+
+static uint64_t bcm2835_rng_read(void *opaque, hwaddr offset,
+                                 unsigned size)
+{
+    BCM2835RngState *s = (BCM2835RngState *)opaque;
+    uint32_t res = 0;
+
+    assert(size == 4);
+
+    switch (offset) {
+    case 0x0:    /* rng_ctrl */
+        res = s->rng_ctrl;
+        break;
+    case 0x4:    /* rng_status */
+        res = s->rng_status | (1 << 24);
+        break;
+    case 0x8:    /* rng_data */
+        res = rand();
+        break;
+
+    default:
+        qemu_log_mask(LOG_GUEST_ERROR,
+                      "bcm2835_rng_read: Bad offset %x\n",
+                      (int)offset);
+        res = 0;
+        break;
+    }
+
+    return res;
+}
+
+static void bcm2835_rng_write(void *opaque, hwaddr offset,
+                              uint64_t value, unsigned size)
+{
+    BCM2835RngState *s = (BCM2835RngState *)opaque;
+
+    assert(size == 4);
+
+    switch (offset) {
+    case 0x0:    /* rng_ctrl */
+        s->rng_ctrl = value;
+        break;
+    case 0x4:    /* rng_status */
+        /* we shouldn't let the guest write to bits [31..20] */
+        s->rng_status &= ~0xFFFFF;        /* clear 20 lower bits */
+        s->rng_status |= value & 0xFFFFF; /* set them to new value */
+        break;
+
+    default:
+        qemu_log_mask(LOG_GUEST_ERROR,
+                      "bcm2835_rng_write: Bad offset %x\n",
+                      (int)offset);
+        break;
+    }
+}
+
+static const MemoryRegionOps bcm2835_rng_ops = {
+    .read = bcm2835_rng_read,
+    .write = bcm2835_rng_write,
+    .endianness = DEVICE_NATIVE_ENDIAN,
+};
+
+static const VMStateDescription vmstate_bcm2835_rng = {
+    .name = TYPE_BCM2835_RNG,
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .fields = (VMStateField[]) {
+        VMSTATE_UINT32(rng_ctrl, BCM2835RngState),
+        VMSTATE_UINT32(rng_status, BCM2835RngState),
+        VMSTATE_END_OF_LIST()
+    }
+};
+
+static void bcm2835_rng_init(Object *obj)
+{
+    BCM2835RngState *s = BCM2835_RNG(obj);
+
+    memory_region_init_io(&s->iomem, obj, &bcm2835_rng_ops, s,
+                          TYPE_BCM2835_RNG, 0x10);
+    sysbus_init_mmio(SYS_BUS_DEVICE(s), &s->iomem);
+}
+
+static void bcm2835_rng_reset(DeviceState *dev)
+{
+    BCM2835RngState *s = BCM2835_RNG(dev);
+
+    s->rng_ctrl = 0;
+    s->rng_status = 0;
+}
+
+static void bcm2835_rng_class_init(ObjectClass *klass, void *data)
+{
+    DeviceClass *dc = DEVICE_CLASS(klass);
+
+    dc->reset = bcm2835_rng_reset;
+    dc->vmsd = &vmstate_bcm2835_rng;
+}
+
+static TypeInfo bcm2835_rng_info = {
+    .name          = TYPE_BCM2835_RNG,
+    .parent        = TYPE_SYS_BUS_DEVICE,
+    .instance_size = sizeof(BCM2835RngState),
+    .class_init    = bcm2835_rng_class_init,
+    .instance_init = bcm2835_rng_init,
+};
+
+static void bcm2835_rng_register_types(void)
+{
+    type_register_static(&bcm2835_rng_info);
+}
+
+type_init(bcm2835_rng_register_types)