virtio: Add codes for virtual queue/ring management

This adds support for managing virtual queue/ring, the channel
for high performance I/O between host and guest.

Signed-off-by: Tuomas Tynkkynen <tuomas.tynkkynen@iki.fi>
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

1 files changed, 320 insertions, 0 deletions

diff --git a/include/virtio_ring.h b/include/virtio_ring.h
new file mode 100644
index 00000000000..6fc0593b14b
--- /dev/null
+++ b/include/virtio_ring.h
@@ -0,0 +1,320 @@
+/* SPDX-License-Identifier: BSD-3-Clause */
+/*
+ * Copyright (C) 2018, Tuomas Tynkkynen <tuomas.tynkkynen@iki.fi>
+ * Copyright (C) 2018, Bin Meng <bmeng.cn@gmail.com>
+ *
+ * From Linux kernel include/uapi/linux/virtio_ring.h
+ */
+
+#ifndef _LINUX_VIRTIO_RING_H
+#define _LINUX_VIRTIO_RING_H
+
+#include <virtio_types.h>
+
+/* This marks a buffer as continuing via the next field */
+#define VRING_DESC_F_NEXT		1
+/* This marks a buffer as write-only (otherwise read-only) */
+#define VRING_DESC_F_WRITE		2
+/* This means the buffer contains a list of buffer descriptors */
+#define VRING_DESC_F_INDIRECT		4
+
+/*
+ * The Host uses this in used->flags to advise the Guest: don't kick me when
+ * you add a buffer. It's unreliable, so it's simply an optimization. Guest
+ * will still kick if it's out of buffers.
+ */
+#define VRING_USED_F_NO_NOTIFY		1
+
+/*
+ * The Guest uses this in avail->flags to advise the Host: don't interrupt me
+ * when you consume a buffer. It's unreliable, so it's simply an optimization.
+ */
+#define VRING_AVAIL_F_NO_INTERRUPT	1
+
+/* We support indirect buffer descriptors */
+#define VIRTIO_RING_F_INDIRECT_DESC	28
+
+/*
+ * The Guest publishes the used index for which it expects an interrupt
+ * at the end of the avail ring. Host should ignore the avail->flags field.
+ *
+ * The Host publishes the avail index for which it expects a kick
+ * at the end of the used ring. Guest should ignore the used->flags field.
+ */
+#define VIRTIO_RING_F_EVENT_IDX		29
+
+/* Virtio ring descriptors: 16 bytes. These can chain together via "next". */
+struct vring_desc {
+	/* Address (guest-physical) */
+	__virtio64 addr;
+	/* Length */
+	__virtio32 len;
+	/* The flags as indicated above */
+	__virtio16 flags;
+	/* We chain unused descriptors via this, too */
+	__virtio16 next;
+};
+
+struct vring_avail {
+	__virtio16 flags;
+	__virtio16 idx;
+	__virtio16 ring[];
+};
+
+struct vring_used_elem {
+	/* Index of start of used descriptor chain */
+	__virtio32 id;
+	/* Total length of the descriptor chain which was used (written to) */
+	__virtio32 len;
+};
+
+struct vring_used {
+	__virtio16 flags;
+	__virtio16 idx;
+	struct vring_used_elem ring[];
+};
+
+struct vring {
+	unsigned int num;
+	struct vring_desc *desc;
+	struct vring_avail *avail;
+	struct vring_used *used;
+};
+
+/**
+ * virtqueue - a queue to register buffers for sending or receiving.
+ *
+ * @list: the chain of virtqueues for this device
+ * @vdev: the virtio device this queue was created for
+ * @index: the zero-based ordinal number for this queue
+ * @num_free: number of elements we expect to be able to fit
+ * @vring: actual memory layout for this queue
+ * @event: host publishes avail event idx
+ * @free_head: head of free buffer list
+ * @num_added: number we've added since last sync
+ * @last_used_idx: last used index we've seen
+ * @avail_flags_shadow: last written value to avail->flags
+ * @avail_idx_shadow: last written value to avail->idx in guest byte order
+ */
+struct virtqueue {
+	struct list_head list;
+	struct udevice *vdev;
+	unsigned int index;
+	unsigned int num_free;
+	struct vring vring;
+	bool event;
+	unsigned int free_head;
+	unsigned int num_added;
+	u16 last_used_idx;
+	u16 avail_flags_shadow;
+	u16 avail_idx_shadow;
+};
+
+/*
+ * Alignment requirements for vring elements.
+ * When using pre-virtio 1.0 layout, these fall out naturally.
+ */
+#define VRING_AVAIL_ALIGN_SIZE		2
+#define VRING_USED_ALIGN_SIZE		4
+#define VRING_DESC_ALIGN_SIZE		16
+
+/*
+ * We publish the used event index at the end of the available ring,
+ * and vice versa. They are at the end for backwards compatibility.
+ */
+#define vring_used_event(vr)	((vr)->avail->ring[(vr)->num])
+#define vring_avail_event(vr)	(*(__virtio16 *)&(vr)->used->ring[(vr)->num])
+
+static inline void vring_init(struct vring *vr, unsigned int num, void *p,
+			      unsigned long align)
+{
+	vr->num = num;
+	vr->desc = p;
+	vr->avail = p + num * sizeof(struct vring_desc);
+	vr->used = (void *)(((uintptr_t)&vr->avail->ring[num] +
+		   sizeof(__virtio16) + align - 1) & ~(align - 1));
+}
+
+static inline unsigned int vring_size(unsigned int num, unsigned long align)
+{
+	return ((sizeof(struct vring_desc) * num +
+		sizeof(__virtio16) * (3 + num)  + align - 1) & ~(align - 1)) +
+		sizeof(__virtio16) * 3 + sizeof(struct vring_used_elem) * num;
+}
+
+/*
+ * The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX.
+ * Assuming a given event_idx value from the other side, if we have just
+ * incremented index from old to new_idx, should we trigger an event?
+ */
+static inline int vring_need_event(__u16 event_idx, __u16 new_idx, __u16 old)
+{
+	/*
+	 * Note: Xen has similar logic for notification hold-off
+	 * in include/xen/interface/io/ring.h with req_event and req_prod
+	 * corresponding to event_idx + 1 and new_idx respectively.
+	 * Note also that req_event and req_prod in Xen start at 1,
+	 * event indexes in virtio start at 0.
+	 */
+	return (__u16)(new_idx - event_idx - 1) < (__u16)(new_idx - old);
+}
+
+struct virtio_sg;
+
+/**
+ * virtqueue_add - expose buffers to other end
+ *
+ * @vq:		the struct virtqueue we're talking about
+ * @sgs:	array of terminated scatterlists
+ * @out_sgs:	the number of scatterlists readable by other side
+ * @in_sgs:	the number of scatterlists which are writable
+ *		(after readable ones)
+ *
+ * Caller must ensure we don't call this with other virtqueue operations
+ * at the same time (except where noted).
+ *
+ * Returns zero or a negative error (ie. ENOSPC, ENOMEM, EIO).
+ */
+int virtqueue_add(struct virtqueue *vq, struct virtio_sg *sgs[],
+		  unsigned int out_sgs, unsigned int in_sgs);
+
+/**
+ * virtqueue_kick - update after add_buf
+ *
+ * @vq:		the struct virtqueue
+ *
+ * After one or more virtqueue_add() calls, invoke this to kick
+ * the other side.
+ *
+ * Caller must ensure we don't call this with other virtqueue
+ * operations at the same time (except where noted).
+ */
+void virtqueue_kick(struct virtqueue *vq);
+
+/**
+ * virtqueue_get_buf - get the next used buffer
+ *
+ * @vq:		the struct virtqueue we're talking about
+ * @len:	the length written into the buffer
+ *
+ * If the device wrote data into the buffer, @len will be set to the
+ * amount written. This means you don't need to clear the buffer
+ * beforehand to ensure there's no data leakage in the case of short
+ * writes.
+ *
+ * Caller must ensure we don't call this with other virtqueue
+ * operations at the same time (except where noted).
+ *
+ * Returns NULL if there are no used buffers, or the memory buffer
+ * handed to virtqueue_add_*().
+ */
+void *virtqueue_get_buf(struct virtqueue *vq, unsigned int *len);
+
+/**
+ * vring_create_virtqueue - create a virtqueue for a virtio device
+ *
+ * @index:	the index of the queue
+ * @num:	number of elements of the queue
+ * @vring_align:the alignment requirement of the descriptor ring
+ * @udev:	the virtio transport udevice
+ * @return: the virtqueue pointer or NULL if failed
+ *
+ * This creates a virtqueue and allocates the descriptor ring for a virtio
+ * device. The caller should query virtqueue_get_ring_size() to learn the
+ * actual size of the ring.
+ *
+ * This API is supposed to be called by the virtio transport driver in the
+ * virtio find_vqs() uclass method.
+ */
+struct virtqueue *vring_create_virtqueue(unsigned int index, unsigned int num,
+					 unsigned int vring_align,
+					 struct udevice *udev);
+
+/**
+ * vring_del_virtqueue - destroy a virtqueue
+ *
+ * @vq:		the struct virtqueue we're talking about
+ *
+ * This destroys a virtqueue. If created with vring_create_virtqueue(),
+ * this also frees the descriptor ring.
+ *
+ * This API is supposed to be called by the virtio transport driver in the
+ * virtio del_vqs() uclass method.
+ */
+void vring_del_virtqueue(struct virtqueue *vq);
+
+/**
+ * virtqueue_get_vring_size - get the size of the virtqueue's vring
+ *
+ * @vq:		the struct virtqueue containing the vring of interest
+ * @return: the size of the vring in a virtqueue.
+ */
+unsigned int virtqueue_get_vring_size(struct virtqueue *vq);
+
+/**
+ * virtqueue_get_desc_addr - get the vring descriptor table address
+ *
+ * @vq:		the struct virtqueue containing the vring of interest
+ * @return: the descriptor table address of the vring in a virtqueue.
+ */
+ulong virtqueue_get_desc_addr(struct virtqueue *vq);
+
+/**
+ * virtqueue_get_avail_addr - get the vring available ring address
+ *
+ * @vq:		the struct virtqueue containing the vring of interest
+ * @return: the available ring address of the vring in a virtqueue.
+ */
+ulong virtqueue_get_avail_addr(struct virtqueue *vq);
+
+/**
+ * virtqueue_get_used_addr - get the vring used ring address
+ *
+ * @vq:		the struct virtqueue containing the vring of interest
+ * @return: the used ring address of the vring in a virtqueue.
+ */
+ulong virtqueue_get_used_addr(struct virtqueue *vq);
+
+/**
+ * virtqueue_poll - query pending used buffers
+ *
+ * @vq:			the struct virtqueue we're talking about
+ * @last_used_idx:	virtqueue last used index
+ *
+ * Returns "true" if there are pending used buffers in the queue.
+ */
+bool virtqueue_poll(struct virtqueue *vq, u16 last_used_idx);
+
+/**
+ * virtqueue_dump - dump the virtqueue for debugging
+ *
+ * @vq:		the struct virtqueue we're talking about
+ *
+ * Caller must ensure we don't call this with other virtqueue operations
+ * at the same time (except where noted).
+ */
+void virtqueue_dump(struct virtqueue *vq);
+
+/*
+ * Barriers in virtio are tricky. Since we are not in a hyperviosr/guest
+ * scenario, having these as nops is enough to work as expected.
+ */
+
+static inline void virtio_mb(void)
+{
+}
+
+static inline void virtio_rmb(void)
+{
+}
+
+static inline void virtio_wmb(void)
+{
+}
+
+static inline void virtio_store_mb(__virtio16 *p, __virtio16 v)
+{
+	WRITE_ONCE(*p, v);
+}
+
+#endif /* _LINUX_VIRTIO_RING_H */