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

6 Sep 2018

      Hi Lukas,
On Wed, Sep 5, 2018 at 5:35 PM Auer, Lukas
lukas.auer@aisec.fraunhofer.de wrote:
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On Wed, 2018-09-05 at 09:28 +0800, Rick Chen wrote:
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From: Auer, Lukas [mailto:lukas.auer@aisec.fraunhofer.de]
Sent: Wednesday, September 05, 2018 5:53 AM
To: bmeng.cn@gmail.com
Cc: Rick Jian-Zhi Chen(陳建志); u-boot@lists.denx.de
Subject: Re: [U-Boot] [PATCH 12/12] riscv: Add QEMU virt board
support
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On Tue, 2018-09-04 at 17:31 +0800, Bin Meng wrote:
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Hi Lukas,
On Tue, Sep 4, 2018 at 5:39 AM Auer, Lukas
lukas.auer@aisec.fraunhofer.de wrote:
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On Thu, 2018-08-30 at 00:54 -0700, Bin Meng wrote:
> This adds QEMU RISC-V 'virt' board target support, with
the hope
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> of helping people easily test U-Boot on RISC-V.
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> The QEMU virt machine models a generic RISC-V virtual
machine
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> with support for the VirtIO standard networking and block
> storage devices.
> It has CLINT, PLIC, 16550A UART devices in addition to
VirtIO
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> and it also uses device-tree to pass configuration
information
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> to guest software. It implements RISC-V privileged
architecture
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> spec v1.10.
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> Both 32-bit and 64-bit builds are supported. Support is
pretty
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> much preliminary, only booting to U-Boot shell with the
UART
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> driver on a single core. Booting Linux is not supported
yet.
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For your information and to avoid duplicate work, I am
working on
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a patch set that improves RISC-V support in u-boot. I am
currently
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able to boot Linux on a multi-core setup in QEMU, but they
are not
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quite ready to submit yet.
This is great! My next step is to work on virtio driver
support in
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U-Boot as qemu-riscv virt machine has these devices but we
don't
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have corresponding drivers in U-Boot. Then I will try to boot
Linux
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after that. Good to hear you already boot Linux with qemu-
riscv!
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Have you already supported virtio drivers in your port? If
yes, I
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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
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my port, I can only boot a kernel image from RAM.
I only have a driver for the clint0 (core local interrupt
controller),
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which I need for software interrupts to other cores and as a
timer.
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Software interrupts also work over the supervisor binary
interface
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(SBI), which allows u-boot to run in supervisor mode with bbl
running
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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.

u-boot SPL starts in machine mode and jumps to bbl
bbl starts u-boot proper in supervisor mode
u-boot boots the kernel

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