[U-Boot] [PATCH 12/12] riscv: Add QEMU virt board support

[Tuomas Tynkkynen]

Hi Bin,

On Fri, 7 Sep 2018 09:49:24 +0800
Bin Meng <bmeng.cn at gmail.com> wrote:

> Hi Tuomas,
> 
> On Fri, Sep 7, 2018 at 5:03 AM Tuomas Tynkkynen
> <tuomas.tynkkynen at iki.fi> wrote:
> >
> > Hi Bin,
> >
> > On 09/04/2018 12:31 PM, Bin Meng wrote:  
> > > Hi Lukas,
> > >
> > > On Tue, Sep 4, 2018 at 5:39 AM Auer, Lukas
> > > <lukas.auer at aisec.fraunhofer.de> wrote:  
> > >>
> > >> On Thu, 2018-08-30 at 00:54 -0700, Bin Meng wrote:  
> > >>> This adds QEMU RISC-V 'virt' board target support, with the
> > >>> hope of helping people easily test U-Boot on RISC-V.
> > >>>
> > >>> The QEMU virt machine models a generic RISC-V virtual machine
> > >>> with support for the VirtIO standard networking and block
> > >>> storage devices. It has CLINT, PLIC, 16550A UART devices in
> > >>> addition to VirtIO and it also uses device-tree to pass
> > >>> configuration information to guest software. It implements
> > >>> RISC-V privileged architecture spec v1.10.
> > >>>
> > >>> Both 32-bit and 64-bit builds are supported. Support is pretty
> > >>> much preliminary, only booting to U-Boot shell with the UART
> > >>> driver on a single core. Booting Linux is not supported yet.
> > >>>  
> > >>
> > >> For your information and to avoid duplicate work, I am working
> > >> on a patch set that improves RISC-V support in u-boot. I am
> > >> currently able to boot Linux on a multi-core setup in QEMU, but
> > >> they are not quite ready to submit yet.
> > >>  
> > >
> > > This is great! My next step is to work on virtio driver support in
> > > U-Boot as qemu-riscv virt machine has these devices but we don't
> > > have corresponding drivers in U-Boot.  
> > At some point I was working on porting the virtio stack from Linux
> > to U-Boot and IIRC got virtio-blk and virtio-net working on ARM.
> > But other things consumed my time and I never quite finished that
> > work. Let me know if you want to take a look.  
> 
> This is great. I just finished reading the virtio 1.0 spec and was
> about to start the work. My interest was to add virtio-blk and
> virtio-net driver to U-Boot too since they are most common devices
> (others are not used too much I believe). If you already have the
> drivers working, I can help to bring them upstream.

You can find my branch here:

https://github.com/dezgeg/u-boot/tree/virtio

It should work under qemu_arm64_defconfig as follows:

qemu-system-aarch64 -machine virt -cpu cortex-a57 -m 512 \
  -bios u-boot.bin -s -nographic \
  -netdev user,id=net0 -device virtio-net-device,netdev=net0 \
  -drive if=none,file=disk.img,id=disk0 \
  -device virtio-blk-device,drive=disk0

I tried with Fedora-Server-netinst-aarch64-28-1.1.iso I had lying
around and letting it auto-boot worked fine.

Also interrupting the boot and doing 'virtio scan; dhcp' gets a
successful DHCP lease from QEMU's internal server.

I took a brief look and these things still need work:

- Some of the virtio headers imported verbatim cause compiler
  warnings because we don't disable strict aliasing.

- Architectures need to import various definitions from Linux.
  At least PAGE_SIZE & PAGE_SHIFT and wmb() & rmb().
  (currently there are just gross hacks around this)

- Feature negotiation (needed for virtio-net to be able to
  set/get a MAC address) is not implemented yet.

- The virtio-pci transport is not implemented, only virtio-mmio.

- Error handling is missing in many places.

- Resource cleanup in some places, like virtio-net which needs to
  remove live buffers from the RX virtqueue on shutdown and I haven't
  looked into how to do that.

- Lots of small things like removing debug/commented out code, wrong
  kerneldoc comments, dead/uneeded code etc. to be cleaned up.

Have fun and let me know if you have questions.

- Tuomas