drivers: entropy: add driver for VirtIO Entropy device

Add VirtIO Entropy driver.

The `virtio,device4` is a somewhat unfamiliar naming convention,
but it follows the convention used in Linux.

Signed-off-by: TOKITA Hiroshi <tokita.hiroshi@gmail.com>

drivers/entropy/CMakeLists.txt

@@ -43,6 +43,7 @@ zephyr_library_sources_ifdef(CONFIG_ENTROPY_SMARTBOND_TRNG      entropy_smartbon
 zephyr_library_sources_ifdef(CONFIG_ENTROPY_STM32_RNG           entropy_stm32.c)
 zephyr_library_sources_ifdef(CONFIG_ENTROPY_SY1XX_TRNG          entropy_sy1xx_trng.c)
 zephyr_library_sources_ifdef(CONFIG_ENTROPY_TELINK_B91_TRNG     entropy_b91_trng.c)
+zephyr_library_sources_ifdef(CONFIG_ENTROPY_VIRTIO              entropy_virtio.c)
 # zephyr-keep-sorted-stop
 
 zephyr_library_link_libraries_ifdef(CONFIG_BUILD_WITH_TFM tfm_api)

drivers/entropy/Kconfig

@@ -45,6 +45,7 @@ source "drivers/entropy/Kconfig.siwx91x"
 source "drivers/entropy/Kconfig.smartbond"
 source "drivers/entropy/Kconfig.stm32"
 source "drivers/entropy/Kconfig.sy1xx"
+source "drivers/entropy/Kconfig.virtio"
 # zephyr-keep-sorted-stop
 
 config ENTROPY_HAS_DRIVER

drivers/entropy/Kconfig.virtio

@@ -0,0 +1,11 @@
+# Copyright (c) 2025 TOKITA Hiroshi
+# SPDX-License-Identifier: Apache-2.0
+
+config ENTROPY_VIRTIO
+	bool "Driver for VirtIO Entropy device"
+	depends on DT_HAS_VIRTIO_DEVICE4_ENABLED
+	depends on VIRTIO
+	select ENTROPY_HAS_DRIVER
+	default y
+	help
+	  Enable driver for the VirtIO Entropy device.

drivers/entropy/entropy_virtio.c

@@ -0,0 +1,114 @@
+/**
+ * Copyright (c) 2025 TOKITA Hiroshi
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <zephyr/drivers/entropy.h>
+#include <zephyr/virtio/virtio.h>
+#include <zephyr/virtio/virtqueue.h>
+#include <zephyr/logging/log.h>
+
+#define VIRTIO_ENTROPY_QUEUE_IDX 0
+
+#define DT_DRV_COMPAT virtio_device4
+
+LOG_MODULE_REGISTER(virtio_entropy, CONFIG_ENTROPY_LOG_LEVEL);
+
+struct entropy_virtio_config {
+	const struct device *vdev;
+};
+
+struct entropy_virtio_data {
+	struct k_sem sem;
+	uint32_t received_len;
+};
+
+static void entropy_virtio_virtq_recv_cb(void *priv, uint32_t len)
+{
+	struct entropy_virtio_data *data = priv;
+
+	data->received_len = len;
+	k_sem_give(&data->sem);
+}
+
+static uint16_t entropy_virtio_enum_queues_cb(uint16_t q_index, uint16_t q_size_max, void *unused)
+{
+	if (q_index == VIRTIO_ENTROPY_QUEUE_IDX) {
+		return MIN(1, q_size_max);
+	}
+
+	return 0;
+}
+
+static int entropy_virtio_get_entropy(const struct device *dev, uint8_t *buffer, uint16_t length)
+{
+	struct virtq_buf buf[] = {{.addr = buffer, .len = length}};
+	const struct entropy_virtio_config *cfg = dev->config;
+	struct entropy_virtio_data *data = dev->data;
+	struct virtq *vq = virtio_get_virtqueue(cfg->vdev, VIRTIO_ENTROPY_QUEUE_IDX);
+	int ret;
+
+	if (!vq) {
+		LOG_ERR("failed to get virtqueue %d", VIRTIO_ENTROPY_QUEUE_IDX);
+		return -ENODEV;
+	}
+
+	data->received_len = 0;
+	ret = virtq_add_buffer_chain(vq, buf, 1, 0, entropy_virtio_virtq_recv_cb, data, K_FOREVER);
+	if (ret) {
+		LOG_ERR("virtq_add_buffer_chain failed: %d", ret);
+		return -EIO;
+	}
+
+	virtio_notify_virtqueue(cfg->vdev, VIRTIO_ENTROPY_QUEUE_IDX);
+
+	k_sem_take(&data->sem, K_FOREVER);
+
+	if (data->received_len != length) {
+		LOG_ERR("insufficient number of values: %d/%d", data->received_len, length);
+		return -EIO;
+	}
+
+	return 0;
+}
+
+static DEVICE_API(entropy, entropy_virtio_api) = {
+	.get_entropy = entropy_virtio_get_entropy,
+};
+
+static int entropy_virtio_init(const struct device *dev)
+{
+	const struct entropy_virtio_config *cfg = dev->config;
+	struct entropy_virtio_data *data = dev->data;
+	int ret;
+
+	ret = virtio_commit_feature_bits(cfg->vdev);
+	if (ret != 0) {
+		return ret;
+	}
+
+	ret = virtio_init_virtqueues(cfg->vdev, 1, entropy_virtio_enum_queues_cb, NULL);
+	if (ret) {
+		LOG_ERR("virtio_init_virtqueues failed: %d", ret);
+		return ret;
+	}
+
+	virtio_finalize_init(cfg->vdev);
+
+	k_sem_init(&data->sem, 0, 1);
+
+	LOG_DBG("VirtIO entropy driver initialized");
+	return 0;
+}
+
+#define ENTROPY_VIRTIO_INST(n)                                                                     \
+	static struct entropy_virtio_data entropy_virtio_data_##n;                                 \
+	static const struct entropy_virtio_config entropy_virtio_config_##n = {                    \
+		.vdev = DEVICE_DT_GET(DT_PARENT(DT_DRV_INST(n))),                                  \
+	};                                                                                         \
+	DEVICE_DT_INST_DEFINE(n, entropy_virtio_init, NULL, &entropy_virtio_data_##n,              \
+			      &entropy_virtio_config_##n, POST_KERNEL,                             \
+			      CONFIG_ENTROPY_INIT_PRIORITY, &entropy_virtio_api);
+
+DT_INST_FOREACH_STATUS_OKAY(ENTROPY_VIRTIO_INST);

dts/bindings/rng/virtio,device4.yaml

@@ -0,0 +1,8 @@
+# Copyright (c) 2025 TOKITA Hiroshi
+# SPDX-License-Identifier: Apache-2.0
+
+description: VirtIO Entropy device (ID:4)
+
+compatible: "virtio,device4"
+
+include: base.yaml