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

[Bin Meng]

Hi Lukas,

On Wed, Sep 5, 2018 at 5:35 PM Auer, Lukas
<lukas.auer at aisec.fraunhofer.de> wrote:
>
> On Wed, 2018-09-05 at 09:28 +0800, Rick Chen 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
> >
> > 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 ?
> > 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 ?
> >
> > Rick
> >
>
> Hi Rick,
>
> Not exactly, my current boot flow is as follows.
>
> 1. u-boot SPL starts in machine mode and jumps to bbl
> 2. bbl starts u-boot proper in supervisor mode
> 3. u-boot boots the kernel
>

If this is QEMU virt target, there is no need to boot from SPL then
U-Boot proper.

> bbl is still active once Linux has booted and is used there for its SBI
> implementation. Hope this helps.

Yes, I am not quite convinced why Linux kernel was designed this way.
This is something like x86's SMM or EFI runtime services...

Regards,
Bin