[PATCH v3 3/6] virtio: 9p: Add 9P transport driver

[Kuan-Wei Chiu <visitorckw@gmail.com>]

Add virtio transport driver for the 9P filesystem.

This driver binds to the virtio-9p device exposed by the hypervisor and
registers as a DM UCLASS_9P device. It implements the transmit and
receive routines.

Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
---
Changes in v3:
- Return received length from virtio_9p_request().
- Call virtio_del_vqs() before virtio_reset() in virtio_9p_remove().
---
 drivers/virtio/Kconfig         |   7 ++
 drivers/virtio/Makefile        |   1 +
 drivers/virtio/virtio-uclass.c |   1 +
 drivers/virtio/virtio_9p.c     | 120 +++++++++++++++++++++++++++++++++
 include/virtio.h               |  12 +++-
 5 files changed, 140 insertions(+), 1 deletion(-)
 create mode 100644 drivers/virtio/virtio_9p.c

diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
index 512ac376f18..55b44428026 100644
--- a/drivers/virtio/Kconfig
+++ b/drivers/virtio/Kconfig
@@ -77,4 +77,11 @@ config VIRTIO_RNG
 	help
 	  This is the virtual random number generator driver. It can be used
 	  with QEMU based targets.
+
+config VIRTIO_9P
+	bool "virtio 9P transport driver"
+	depends on VIRTIO && NET_9P
+	help
+	  This enables the 9P transport driver over virtio.
+	  It can be used with QEMU based targets.
 endmenu
diff --git a/drivers/virtio/Makefile b/drivers/virtio/Makefile
index 4c63a6c6904..6e7bcfc8eaa 100644
--- a/drivers/virtio/Makefile
+++ b/drivers/virtio/Makefile
@@ -11,3 +11,4 @@ obj-$(CONFIG_VIRTIO_SANDBOX) += virtio_sandbox.o
 obj-$(CONFIG_VIRTIO_NET) += virtio_net.o
 obj-$(CONFIG_VIRTIO_BLK) += virtio_blk.o
 obj-$(CONFIG_VIRTIO_RNG) += virtio_rng.o
+obj-$(CONFIG_VIRTIO_9P) += virtio_9p.o
diff --git a/drivers/virtio/virtio-uclass.c b/drivers/virtio/virtio-uclass.c
index a871a1439d4..c163b2fd7d5 100644
--- a/drivers/virtio/virtio-uclass.c
+++ b/drivers/virtio/virtio-uclass.c
@@ -30,6 +30,7 @@ static const char *const virtio_drv_name[VIRTIO_ID_MAX_NUM] = {
 	[VIRTIO_ID_NET]		= VIRTIO_NET_DRV_NAME,
 	[VIRTIO_ID_BLOCK]	= VIRTIO_BLK_DRV_NAME,
 	[VIRTIO_ID_RNG]		= VIRTIO_RNG_DRV_NAME,
+	[VIRTIO_ID_9P]		= VIRTIO_9P_DRV_NAME,
 };
 
 int virtio_get_config(struct udevice *vdev, unsigned int offset,
diff --git a/drivers/virtio/virtio_9p.c b/drivers/virtio/virtio_9p.c
new file mode 100644
index 00000000000..fb2eb0c7223
--- /dev/null
+++ b/drivers/virtio/virtio_9p.c
@@ -0,0 +1,120 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2026, Kuan-Wei Chiu <visitorckw@gmail.com>
+ */
+
+#define LOG_CATEGORY UCLASS_VIRTIO
+
+#include <9p.h>
+#include <dm.h>
+#include <time.h>
+#include <virtio.h>
+#include <virtio_ring.h>
+#include <virtio_types.h>
+#include <linux/errno.h>
+
+#define VIRTIO_9P_TIMEOUT_MS 5000
+
+struct virtio_9p_priv {
+	struct virtqueue *vq;
+	char mount_tag[32];
+};
+
+static const u32 feature[] = {
+	VIRTIO_9P_MOUNT_TAG,
+};
+
+static int virtio_9p_request(struct udevice *dev, void *tx, int tx_len, void *rx, int rx_len)
+{
+	struct virtio_9p_priv *priv = dev_get_priv(dev);
+	struct virtio_sg sg[2];
+	struct virtio_sg *sgs[2];
+	int len, ret;
+	ulong start;
+
+	sg[0].addr = tx;
+	sg[0].length = tx_len;
+	sgs[0] = &sg[0];
+
+	sg[1].addr = rx;
+	sg[1].length = rx_len;
+	sgs[1] = &sg[1];
+
+	ret = virtqueue_add(priv->vq, sgs, 1, 1);
+	if (ret)
+		return ret;
+
+	virtqueue_kick(priv->vq);
+
+	start = get_timer(0);
+	while (!virtqueue_get_buf(priv->vq, &len)) {
+		if (get_timer(start) > VIRTIO_9P_TIMEOUT_MS)
+			return -ETIMEDOUT;
+	}
+
+	if (len < (int)sizeof(struct p9_header))
+		return -EIO;
+
+	return len;
+}
+
+static const char *virtio_9p_get_mount_tag(struct udevice *dev)
+{
+	struct virtio_9p_priv *priv = dev_get_priv(dev);
+
+	return priv->mount_tag;
+}
+
+static const struct dm_p9_ops virtio_9p_ops = {
+	.request = virtio_9p_request,
+	.get_mount_tag = virtio_9p_get_mount_tag,
+};
+
+static int virtio_9p_bind(struct udevice *dev)
+{
+	struct virtio_dev_priv *uc_priv = dev_get_uclass_priv(dev->parent);
+
+	virtio_driver_features_init(uc_priv, feature, ARRAY_SIZE(feature), NULL, 0);
+	return 0;
+}
+
+static int virtio_9p_probe(struct udevice *dev)
+{
+	struct virtio_9p_priv *priv = dev_get_priv(dev);
+	int ret;
+
+	ret = virtio_find_vqs(dev, 1, &priv->vq);
+	if (ret)
+		return ret;
+
+	if (virtio_has_feature(dev, VIRTIO_9P_MOUNT_TAG)) {
+		u16 tag_len;
+
+		virtio_cread(dev, struct virtio_9p_config, tag_len, &tag_len);
+		if (tag_len > 0 && tag_len < sizeof(priv->mount_tag)) {
+			virtio_cread_bytes(dev, offsetof(struct virtio_9p_config, tag),
+					   priv->mount_tag, tag_len);
+			priv->mount_tag[tag_len] = '\0';
+			log_debug("virtio-9p: mount_tag=%s\n", priv->mount_tag);
+		}
+	}
+
+	return 0;
+}
+
+static int virtio_9p_remove(struct udevice *dev)
+{
+	virtio_del_vqs(dev);
+	return virtio_reset(dev);
+}
+
+U_BOOT_DRIVER(virtio_9p) = {
+	.name       = VIRTIO_9P_DRV_NAME,
+	.id         = UCLASS_9P,
+	.ops        = &virtio_9p_ops,
+	.bind       = virtio_9p_bind,
+	.probe      = virtio_9p_probe,
+	.remove     = virtio_9p_remove,
+	.priv_auto  = sizeof(struct virtio_9p_priv),
+	.flags      = DM_FLAG_ACTIVE_DMA,
+};
diff --git a/include/virtio.h b/include/virtio.h
index 3edf023463d..b981eead5d7 100644
--- a/include/virtio.h
+++ b/include/virtio.h
@@ -31,11 +31,21 @@
 #define VIRTIO_ID_NET		1 /* virtio net */
 #define VIRTIO_ID_BLOCK		2 /* virtio block */
 #define VIRTIO_ID_RNG		4 /* virtio rng */
-#define VIRTIO_ID_MAX_NUM	5
+#define VIRTIO_ID_9P		9 /* virtio 9p */
+#define VIRTIO_ID_MAX_NUM	10
 
 #define VIRTIO_NET_DRV_NAME	"virtio-net"
 #define VIRTIO_BLK_DRV_NAME	"virtio-blk"
 #define VIRTIO_RNG_DRV_NAME	"virtio-rng"
+#define VIRTIO_9P_DRV_NAME	"virtio-9p"
+
+/* Feature bits for virtio 9P */
+#define VIRTIO_9P_MOUNT_TAG	0
+
+struct virtio_9p_config {
+	__virtio16 tag_len;
+	u8 tag[];
+} __packed;
 
 /* Status byte for guest to report progress, and synchronize features */
 
-- 
2.56.0.rc1.310.g51773c2048-goog