mirror of
https://github.com/AsahiLinux/u-boot
synced 2024-11-10 15:14:43 +00:00
doc: Document virtio support
Add REAME.virtio to describe the information about U-Boot support for VirtIO devices, including supported boards, build instructions, driver details etc. Signed-off-by: Bin Meng <bmeng.cn@gmail.com> Reviewed-by: Simon Glass <sjg@chromium.org>
This commit is contained in:
Bin Meng
Simon Glass
parent
4f89d4947c
commit
216460ec12
1 changed files with 253 additions and 0 deletions
253
doc/README.virtio
Normal file
253
doc/README.virtio
Normal file
|
|
@ -0,0 +1,253 @@
|
||||||
|
# SPDX-License-Identifier: GPL-2.0+
|
||||||
|
#
|
||||||
|
# Copyright (C) 2018, Bin Meng <bmeng.cn@gmail.com>
|
||||||
|
|
||||||
|
VirtIO Support
|
||||||
|
==============
|
||||||
|
|
||||||
|
This document describes the information about U-Boot support for VirtIO [1]
|
||||||
|
devices, including supported boards, build instructions, driver details etc.
|
||||||
|
|
||||||
|
What's VirtIO?
|
||||||
|
--------------
|
||||||
|
VirtIO is a virtualization standard for network and disk device drivers where
|
||||||
|
just the guest's device driver "knows" it is running in a virtual environment,
|
||||||
|
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.
|
||||||
|
|
||||||
|
Status
|
||||||
|
------
|
||||||
|
VirtIO can use various different buses, aka transports as described in the
|
||||||
|
spec. While VirtIO devices are commonly implemented as PCI devices on x86,
|
||||||
|
embedded devices models like ARM/RISC-V, which does not normally come with
|
||||||
|
PCI support might use simple memory mapped device (MMIO) instead of the PCI
|
||||||
|
device. The memory mapped virtio device behaviour is based on the PCI device
|
||||||
|
specification. Therefore most operations including device initialization,
|
||||||
|
queues configuration and buffer transfers are nearly identical. Both MMIO
|
||||||
|
and PCI transport options are supported in U-Boot.
|
||||||
|
|
||||||
|
The VirtIO spec defines a lots of VirtIO device types, however at present only
|
||||||
|
network and block device, the most two commonly used devices, are supported.
|
||||||
|
|
||||||
|
The following QEMU targets are supported.
|
||||||
|
|
||||||
|
- qemu_arm_defconfig
|
||||||
|
- qemu_arm64_defconfig
|
||||||
|
- qemu-riscv32_defconfig
|
||||||
|
- qemu-riscv64_defconfig
|
||||||
|
- qemu-x86_defconfig
|
||||||
|
- qemu-x86_64_defconfig
|
||||||
|
|
||||||
|
Note ARM and RISC-V targets are configured with VirtIO MMIO transport driver,
|
||||||
|
and on x86 it's the PCI transport driver.
|
||||||
|
|
||||||
|
Build Instructions
|
||||||
|
------------------
|
||||||
|
Building U-Boot for pre-configured QEMU targets is no different from others.
|
||||||
|
For example, we can do the following with the CROSS_COMPILE environment
|
||||||
|
variable being properly set to a working toolchain for ARM:
|
||||||
|
|
||||||
|
$ make qemu_arm_defconfig
|
||||||
|
$ make
|
||||||
|
|
||||||
|
You can even create a QEMU ARM target with VirtIO devices showing up on both
|
||||||
|
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
|
||||||
|
|
||||||
|
Other drivers are at the same location and can be tuned to suit the needs.
|
||||||
|
|
||||||
|
Requirements
|
||||||
|
------------
|
||||||
|
It is required that QEMU v2.5.0+ should be used to test U-Boot VirtIO support
|
||||||
|
on QEMU ARM and x86, and v2.12.0+ on QEMU RISC-V.
|
||||||
|
|
||||||
|
Testing
|
||||||
|
-------
|
||||||
|
The following QEMU command line is used to get U-Boot up and running with
|
||||||
|
VirtIO net and block devices on ARM.
|
||||||
|
|
||||||
|
$ qemu-system-arm -nographic -machine virt -bios u-boot.bin \
|
||||||
|
-netdev tap,ifname=tap0,id=net0 \
|
||||||
|
-device virtio-net-device,netdev=net0 \
|
||||||
|
-drive if=none,file=test.img,format=raw,id=hd0 \
|
||||||
|
-device virtio-blk-device,drive=hd0
|
||||||
|
|
||||||
|
On x86, command is slightly different to create PCI VirtIO devices.
|
||||||
|
|
||||||
|
$ qemu-system-i386 -nographic -bios u-boot.rom \
|
||||||
|
-netdev tap,ifname=tap0,id=net0 \
|
||||||
|
-device virtio-net-pci,netdev=net0 \
|
||||||
|
-drive if=none,file=test.img,format=raw,id=hd0 \
|
||||||
|
-device virtio-blk-pci,drive=hd0
|
||||||
|
|
||||||
|
Additional net and block devices can be created by appending more '-device'
|
||||||
|
parameters. It is also possible to specify both MMIO and PCI VirtIO devices.
|
||||||
|
For example, the following commnad creates 3 VirtIO devices, with 1 on MMIO
|
||||||
|
and 2 on PCI bus.
|
||||||
|
|
||||||
|
$ qemu-system-arm -nographic -machine virt -bios u-boot.bin \
|
||||||
|
-netdev tap,ifname=tap0,id=net0 \
|
||||||
|
-device virtio-net-pci,netdev=net0 \
|
||||||
|
-drive if=none,file=test0.img,format=raw,id=hd0 \
|
||||||
|
-device virtio-blk-device,drive=hd0 \
|
||||||
|
-drive if=none,file=test1.img,format=raw,id=hd1 \
|
||||||
|
-device virtio-blk-pci,drive=hd1
|
||||||
|
|
||||||
|
By default QEMU creates VirtIO legacy devices by default. To create non-legacy
|
||||||
|
(aka modern) devices, pass additional device property/value pairs like below:
|
||||||
|
|
||||||
|
$ 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 \
|
||||||
|
-drive if=none,file=test.img,format=raw,id=hd0 \
|
||||||
|
-device virtio-blk-pci,drive=hd0,disable-legacy=true,disable-modern=false
|
||||||
|
|
||||||
|
A 'virtio' command is provided in U-Boot shell.
|
||||||
|
|
||||||
|
=> virtio
|
||||||
|
virtio - virtio block devices sub-system
|
||||||
|
|
||||||
|
Usage:
|
||||||
|
virtio scan - initialize virtio bus
|
||||||
|
virtio info - show all available virtio block devices
|
||||||
|
virtio device [dev] - show or set current virtio block device
|
||||||
|
virtio part [dev] - print partition table of one or all virtio block devices
|
||||||
|
virtio read addr blk# cnt - read `cnt' blocks starting at block
|
||||||
|
`blk#' to memory address `addr'
|
||||||
|
virtio write addr blk# cnt - write `cnt' blocks starting at block
|
||||||
|
`blk#' from memory address `addr'
|
||||||
|
|
||||||
|
To probe all the VirtIO devices, type:
|
||||||
|
|
||||||
|
=> virtio scan
|
||||||
|
|
||||||
|
Then we can show the connected block device details by:
|
||||||
|
|
||||||
|
=> virtio info
|
||||||
|
Device 0: QEMU VirtIO Block Device
|
||||||
|
Type: Hard Disk
|
||||||
|
Capacity: 4096.0 MB = 4.0 GB (8388608 x 512)
|
||||||
|
|
||||||
|
And list the directories and files on the disk by:
|
||||||
|
|
||||||
|
=> ls virtio 0 /
|
||||||
|
<DIR> 4096 .
|
||||||
|
<DIR> 4096 ..
|
||||||
|
<DIR> 16384 lost+found
|
||||||
|
<DIR> 4096 dev
|
||||||
|
<DIR> 4096 proc
|
||||||
|
<DIR> 4096 sys
|
||||||
|
<DIR> 4096 var
|
||||||
|
<DIR> 4096 etc
|
||||||
|
<DIR> 4096 usr
|
||||||
|
<SYM> 7 bin
|
||||||
|
<SYM> 8 sbin
|
||||||
|
<SYM> 7 lib
|
||||||
|
<SYM> 9 lib64
|
||||||
|
<DIR> 4096 run
|
||||||
|
<DIR> 4096 boot
|
||||||
|
<DIR> 4096 home
|
||||||
|
<DIR> 4096 media
|
||||||
|
<DIR> 4096 mnt
|
||||||
|
<DIR> 4096 opt
|
||||||
|
<DIR> 4096 root
|
||||||
|
<DIR> 4096 srv
|
||||||
|
<DIR> 4096 tmp
|
||||||
|
0 .autorelabel
|
||||||
|
|
||||||
|
Driver Internals
|
||||||
|
----------------
|
||||||
|
There are 3 level of drivers in the VirtIO driver family.
|
||||||
|
|
||||||
|
+---------------------------------------+
|
||||||
|
| virtio device drivers |
|
||||||
|
| +-------------+ +------------+ |
|
||||||
|
| | virtio-net | | virtio-blk | |
|
||||||
|
| +-------------+ +------------+ |
|
||||||
|
+---------------------------------------+
|
||||||
|
+---------------------------------------+
|
||||||
|
| virtio transport drivers |
|
||||||
|
| +-------------+ +------------+ |
|
||||||
|
| | virtio-mmio | | virtio-pci | |
|
||||||
|
| +-------------+ +------------+ |
|
||||||
|
+---------------------------------------+
|
||||||
|
+----------------------+
|
||||||
|
| virtio uclass driver |
|
||||||
|
+----------------------+
|
||||||
|
|
||||||
|
The root one is the virtio uclass driver (virtio-uclass.c), which does lots of
|
||||||
|
common stuff for the transport drivers (virtio_mmio.c, virtio_pci.c). The real
|
||||||
|
virtio device is discovered in the transport driver's probe() method, and its
|
||||||
|
device ID is saved in the virtio uclass's private data of the transport device.
|
||||||
|
Then in the virtio uclass's post_probe() method, the real virtio device driver
|
||||||
|
(virtio_net.c, virtio_blk.c) is bound if there is a match on the device ID.
|
||||||
|
|
||||||
|
The child_post_bind(), child_pre_probe() and child_post_probe() methods of the
|
||||||
|
virtio uclass driver help bring the virtio device driver online. They do things
|
||||||
|
like acknowledging device, feature negotiation, etc, which are really common
|
||||||
|
for all virtio devices.
|
||||||
|
|
||||||
|
The transport drivers provide a set of ops (struct dm_virtio_ops) for the real
|
||||||
|
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)
|
||||||
|
|
||||||
|
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)
|
||||||
|
|
||||||
|
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)
|
||||||
|
|
||||||
|
So it's easy to tell which device these functions are operating on.
|
||||||
|
|
||||||
|
Development Flow
|
||||||
|
----------------
|
||||||
|
At present only VirtIO network card (device ID 1) and block device (device
|
||||||
|
ID 2) are supported. If you want to develop new driver for new devices,
|
||||||
|
please follow the guideline below.
|
||||||
|
|
||||||
|
1. add new device ID in virtio.h
|
||||||
|
#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"
|
||||||
|
|
||||||
|
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,
|
||||||
|
}
|
||||||
|
|
||||||
|
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
|
||||||
|
for the remove method to be called before jumping to OS.
|
||||||
|
|
||||||
|
5. provide bind() method in the driver, where virtio_driver_features_init()
|
||||||
|
should be called for driver to negotiate feature support with the device.
|
||||||
|
|
||||||
|
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
|
||||||
Loading…
Reference in a new issue