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

[Bin Meng]

Hi Rick,

On Wed, Sep 5, 2018 at 9:27 AM Rick Chen <rickchen36 at gmail.com> wrote:
>
>  > > From: Auer, Lukas [mailto:lukas.auer at aisec.fraunhofer.de]
>  > > Sent: Wednesday, September 05, 2018 5:53 AM
>  > > To: bmeng.cn at gmail.com
>  > > Cc: Rick Jian-Zhi Chen(陳建志); u-boot at lists.denx.de
>  > > Subject: Re: [U-Boot] [PATCH 12/12] riscv: Add QEMU virt board support
>  > >
>  > > On Tue, 2018-09-04 at 17:31 +0800, 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. Then I will try to boot Linux
>  > > > after that. Good to hear you already boot Linux with qemu-riscv!
>  > > > Have you already supported virtio drivers in your port? If yes, I
>  > > > will just hold on and wait for your patch series :-)
>  > > >
>  > >
>  > > Hi Bin,
>  > >
>  > > Support for the virtio devices would be great! I don't support them in
>  > > my port, I can only boot a kernel image from RAM.
>  > > I only have a driver for the clint0 (core local interrupt controller),
>  > > which I need for software interrupts to other cores and as a timer.
>  > > Software interrupts also work over the supervisor binary interface
>  > > (SBI), which allows u-boot to run in supervisor mode with bbl running
>  > > in machine mode to handle the SBI calls.
>  > >
>
> Hi Bin and Auer
>
> I have already boot bbl run in S-mode and riscv-linux in M-mode via
> u-boot from SD card or FLASH.
> It mean after booting riscv-linux, u-boot will be dead. And no matter
> about kernel.
> Please refer to doc/README.ae350
>

Thanks for pointing out the doc for ae350. I just read it, and have
one question. There is a chapter in that doc "Boot bbl and riscv-linux
via U-Boot on QEMU", yet I don't see what QEMU command is invoked. Can
you please clarify? AFAIK mainline QEMU does not have support to ae350
board. Also there is no instructions on how bbl was built. Is that the
mainline bbl that can work on every riscv board? I doubt that.

> May I figure out more clearly what are you going to do ?
> What are you going to do is let u-boot run in S-mode and boot bbl and
> riscv-linux in M-mode, right ?

I want to use U-Boot to directly boot Linux, but seems Lukas is using
bbl for SBI implementation.

> It mean after booting bbl and riscv-linux, u-boot will still alive and
> handle SBI calls and somethings in S-mode.
>
> Or u-boot is going to replace the role of bbl ?
>

That's my plan. I don't see a need to use bbl which is quite feature limited.

Regards,
Bin