-# SPDX-License-Identifier: GPL-2.0+
-#
-# Copyright (C) 2018, Bin Meng <bmeng.cn@gmail.com>
+.. SPDX-License-Identifier: GPL-2.0+
+.. sectionauthor:: Bin Meng <bmeng.cn@gmail.com>
VirtIO Support
==============
-This document describes the information about U-Boot support for VirtIO [1]
+This document describes the information about U-Boot support for VirtIO_
devices, including supported boards, build instructions, driver details etc.
What's VirtIO?
and cooperates with the hypervisor. This enables guests to get high performance
network and disk operations, and gives most of the performance benefits of
paravirtualization. In the U-Boot case, the guest is U-Boot itself, while the
-virtual environment are normally QEMU [2] targets like ARM, RISC-V and x86.
+virtual environment are normally QEMU_ targets like ARM, RISC-V and x86.
Status
------
For example, we can do the following with the CROSS_COMPILE environment
variable being properly set to a working toolchain for ARM:
+.. code-block:: bash
+
$ make qemu_arm_defconfig
$ make
MMIO and PCI buses. In this case, you can enable the PCI transport driver
from 'make menuconfig':
-Device Drivers --->
- ...
- VirtIO Drivers --->
- ...
- [*] PCI driver for virtio devices
+.. code-block:: none
+
+ Device Drivers --->
+ ...
+ VirtIO Drivers --->
+ ...
+ [*] PCI driver for virtio devices
Other drivers are at the same location and can be tuned to suit the needs.
The following QEMU command line is used to get U-Boot up and running with
VirtIO net and block devices on ARM.
+.. code-block:: bash
+
$ qemu-system-arm -nographic -machine virt -bios u-boot.bin \
-netdev tap,ifname=tap0,id=net0 \
-device virtio-net-device,netdev=net0 \
On x86, command is slightly different to create PCI VirtIO devices.
+.. code-block:: bash
+
$ qemu-system-i386 -nographic -bios u-boot.rom \
-netdev tap,ifname=tap0,id=net0 \
-device virtio-net-pci,netdev=net0 \
For example, the following commnad creates 3 VirtIO devices, with 1 on MMIO
and 2 on PCI bus.
+.. code-block:: bash
+
$ qemu-system-arm -nographic -machine virt -bios u-boot.bin \
-netdev tap,ifname=tap0,id=net0 \
-device virtio-net-pci,netdev=net0 \
By default QEMU creates VirtIO legacy devices by default. To create non-legacy
(aka modern) devices, pass additional device property/value pairs like below:
+.. code-block:: bash
+
$ qemu-system-i386 -nographic -bios u-boot.rom \
-netdev tap,ifname=tap0,id=net0 \
-device virtio-net-pci,netdev=net0,disable-legacy=true,disable-modern=false \
A 'virtio' command is provided in U-Boot shell.
+.. code-block:: none
+
=> virtio
virtio - virtio block devices sub-system
To probe all the VirtIO devices, type:
+.. code-block:: none
+
=> virtio scan
Then we can show the connected block device details by:
+.. code-block:: none
+
=> virtio info
Device 0: QEMU VirtIO Block Device
Type: Hard Disk
And list the directories and files on the disk by:
+.. code-block:: none
+
=> ls virtio 0 /
<DIR> 4096 .
<DIR> 4096 ..
----------------
There are 3 level of drivers in the VirtIO driver family.
+.. code-block:: none
+
+---------------------------------------+
| virtio device drivers |
| +-------------+ +------------+ |
virtio device driver to call. These ops APIs's parameter is designed to remind
the caller to pass the correct 'struct udevice' id of the virtio device, eg:
-int virtio_get_status(struct udevice *vdev, u8 *status)
+.. code-block:: C
+
+ int virtio_get_status(struct udevice *vdev, u8 *status)
So the parameter 'vdev' indicates the device should be the real virtio device.
But we also have an API like:
-struct virtqueue *vring_create_virtqueue(unsigned int index, unsigned int num,
- unsigned int vring_align,
- struct udevice *udev)
+.. code-block:: C
+
+ struct virtqueue *vring_create_virtqueue(unsigned int index, unsigned int num,
+ unsigned int vring_align,
+ struct udevice *udev)
Here the parameter 'udev' indicates the device should be the transport device.
Similar naming is applied in other functions that are even not APIs, eg:
-static int virtio_uclass_post_probe(struct udevice *udev)
-static int virtio_uclass_child_pre_probe(struct udevice *vdev)
+.. code-block:: C
+
+ static int virtio_uclass_post_probe(struct udevice *udev)
+ static int virtio_uclass_child_pre_probe(struct udevice *vdev)
So it's easy to tell which device these functions are operating on.
please follow the guideline below.
1. add new device ID in virtio.h
-#define VIRTIO_ID_XXX X
+
+.. code-block:: C
+
+ #define VIRTIO_ID_XXX X
2. update VIRTIO_ID_MAX_NUM to be the largest device ID plus 1
3. add new driver name string in virtio.h
-#define VIRTIO_XXX_DRV_NAME "virtio-xxx"
+
+.. code-block:: C
+
+ #define VIRTIO_XXX_DRV_NAME "virtio-xxx"
4. create a new driver with name set to the name string above
-U_BOOT_DRIVER(virtio_xxx) = {
- .name = VIRTIO_XXX_DRV_NAME,
- ...
- .remove = virtio_reset,
- .flags = DM_FLAG_ACTIVE_DMA,
-}
+
+.. code-block:: C
+
+ U_BOOT_DRIVER(virtio_xxx) = {
+ .name = VIRTIO_XXX_DRV_NAME,
+ ...
+ .remove = virtio_reset,
+ .flags = DM_FLAG_ACTIVE_DMA,
+ }
Note the driver needs to provide the remove method and normally this can be
hooked to virtio_reset(). The driver flags should contain DM_FLAG_ACTIVE_DMA
6. do funny stuff with the driver
-References
-----------
-[1] http://docs.oasis-open.org/virtio/virtio/v1.0/virtio-v1.0.pdf
-[2] https://www.qemu.org
+.. _VirtIO: http://docs.oasis-open.org/virtio/virtio/v1.0/virtio-v1.0.pdf
+.. _QEMU: https://www.qemu.org