Re: [PATCH 2/2] docs/system: riscv: Add documentation for virt machine

[Alistair Francis <alistair23@gmail.com>]

On Mon, Jun 28, 2021 at 12:29 AM Bin Meng <bmeng.cn@gmail.com> wrote:
>
> This adds detailed documentation for RISC-V `virt` machine,
> including the following information:
>
>   - Supported devices
>   - Hardware configuration information
>   - Boot options
>   - Running Linux kernel
>   - Running U-Boot
>
> Signed-off-by: Bin Meng <bmeng.cn@gmail.com>

Reviewed-by: Alistair Francis <alistair.francis@wdc.com>

Alistair

> ---
>
>  docs/system/riscv/virt.rst   | 138 +++++++++++++++++++++++++++++++++++
>  docs/system/target-riscv.rst |   1 +
>  2 files changed, 139 insertions(+)
>  create mode 100644 docs/system/riscv/virt.rst
>
> diff --git a/docs/system/riscv/virt.rst b/docs/system/riscv/virt.rst
> new file mode 100644
> index 0000000000..3709f05797
> --- /dev/null
> +++ b/docs/system/riscv/virt.rst
> @@ -0,0 +1,138 @@
> +'virt' Generic Virtual Platform (``virt``)
> +==========================================
> +
> +The `virt` board is a platform which does not correspond to any real hardware;
> +it is designed for use in virtual machines. It is the recommended board type
> +if you simply want to run a guest such as Linux and do not care about
> +reproducing the idiosyncrasies and limitations of a particular bit of
> +real-world hardware.
> +
> +Supported devices
> +-----------------
> +
> +The ``virt`` machine supports the following devices:
> +
> +* Up to 8 generic RV32GC/RV64GC cores, with optional extensions
> +* Core Local Interruptor (CLINT)
> +* Platform-Level Interrupt Controller (PLIC)
> +* CFI parallel NOR flash memory
> +* 1 NS16550 compatible UART
> +* 1 Google Goldfish RTC
> +* 1 SiFive Test device
> +* 8 virtio-mmio transport devices
> +* 1 generic PCIe host bridge
> +* The fw_cfg device that allows a guest to obtain data from QEMU
> +
> +Note that the default CPU is a generic RV32GC/RV64GC. Optional extensions
> +can be enabled via command line parameters, e.g.: ``-cpu rv64,x-h=true``
> +enables the hypervisor extension for RV64.
> +
> +Hardware configuration information
> +----------------------------------
> +
> +The ``virt`` machine automatically generates a device tree blob ("dtb")
> +which it passes to the guest, if there is no ``-dtb`` option. This provides
> +information about the addresses, interrupt lines and other configuration of
> +the various devices in the system. Guest software should discover the devices
> +that are present in the generated DTB.
> +
> +If users want to provide their own DTB, they can use the ``-dtb`` option.
> +These DTBs should have the following requirements:
> +
> +* The number of subnodes of the /cpus node should match QEMU's ``-smp`` option
> +* The /memory reg size should match QEMU’s selected ram_size via ``-m``
> +* Should contain a node for the CLINT device with a compatible string
> +  "riscv,clint0" if using with OpenSBI BIOS images
> +
> +Boot options
> +------------
> +
> +The ``virt`` machine can start using the standard -kernel functionality
> +for loading a Linux kernel, a VxWorks kernel, an S-mode U-Boot bootloader
> +with the default OpenSBI firmware image as the -bios. It also supports
> +the recommended RISC-V bootflow: U-Boot SPL (M-mode) loads OpenSBI fw_dynamic
> +firmware and U-Boot proper (S-mode), using the standard -bios functionality.
> +
> +Running Linux kernel
> +--------------------
> +
> +Linux mainline v5.12 release is tested at the time of writing. To build a
> +Linux mainline kernel that can be booted by the ``virt`` machine in
> +64-bit mode, simply configure the kernel using the defconfig configuration:
> +
> +.. code-block:: bash
> +
> +  $ export ARCH=riscv
> +  $ export CROSS_COMPILE=riscv64-linux-
> +  $ make defconfig
> +  $ make
> +
> +To boot the newly built Linux kernel in QEMU with the ``virt`` machine:
> +
> +.. code-block:: bash
> +
> +  $ qemu-system-riscv64 -M virt -smp 4 -m 2G \
> +      -display none -serial stdio \
> +      -kernel arch/riscv/boot/Image \
> +      -initrd /path/to/rootfs.cpio \
> +      -append "root=/dev/ram"
> +
> +To build a Linux mainline kernel that can be booted by the ``virt`` machine
> +in 32-bit mode, use the rv32_defconfig configuration. A patch is required to
> +fix the 32-bit boot issue for Linux kernel v5.12.
> +
> +.. code-block:: bash
> +
> +  $ export ARCH=riscv
> +  $ export CROSS_COMPILE=riscv64-linux-
> +  $ curl https://patchwork.kernel.org/project/linux-riscv/patch/20210627135117.28641-1-bmeng.cn@gmail.com/mbox/ > riscv.patch
> +  $ git am riscv.patch
> +  $ make rv32_defconfig
> +  $ make
> +
> +Replace ``qemu-system-riscv64`` with ``qemu-system-riscv32`` in the command
> +line above to boot the 32-bit Linux kernel. A rootfs image containing 32-bit
> +applications shall be used in order for kernel to boot to user space.
> +
> +Running U-Boot
> +--------------
> +
> +U-Boot mainline v2021.04 release is tested at the time of writing. To build an
> +S-mode U-Boot bootloader that can be booted by the ``virt`` machine, use
> +the qemu-riscv64_smode_defconfig with similar commands as described above for Linux:
> +
> +.. code-block:: bash
> +
> +  $ export CROSS_COMPILE=riscv64-linux-
> +  $ make qemu-riscv64_smode_defconfig
> +
> +Boot the 64-bit U-Boot S-mode image directly:
> +
> +.. code-block:: bash
> +
> +  $ qemu-system-riscv64 -M virt -smp 4 -m 2G \
> +      -display none -serial stdio \
> +      -kernel /path/to/u-boot.bin
> +
> +To test booting U-Boot SPL which in M-mode, which in turn loads a FIT image
> +that bundles OpenSBI fw_dynamic firmware and U-Boot proper (S-mode) together,
> +build the U-Boot images using riscv64_spl_defconfig:
> +
> +.. code-block:: bash
> +
> +  $ export CROSS_COMPILE=riscv64-linux-
> +  $ export OPENSBI=/path/to/opensbi-riscv64-generic-fw_dynamic.bin
> +  $ make qemu-riscv64_spl_defconfig
> +
> +The minimal QEMU commands to run U-Boot SPL are:
> +
> +.. code-block:: bash
> +
> +  $ qemu-system-riscv64 -M virt -smp 4 -m 2G \
> +      -display none -serial stdio \
> +      -bios /path/to/u-boot-spl \
> +      -device loader,file=/path/to/u-boot.itb,addr=0x80200000
> +
> +To test 32-bit U-Boot images, switch to use qemu-riscv32_smode_defconfig and
> +riscv32_spl_defconfig builds, and replace ``qemu-system-riscv64`` with
> +``qemu-system-riscv32`` in the command lines above to boot the 32-bit U-Boot.
> diff --git a/docs/system/target-riscv.rst b/docs/system/target-riscv.rst
> index a5cc06b726..89a866e4f4 100644
> --- a/docs/system/target-riscv.rst
> +++ b/docs/system/target-riscv.rst
> @@ -69,6 +69,7 @@ undocumented; you can get a complete list by running
>     riscv/microchip-icicle-kit
>     riscv/shakti-c
>     riscv/sifive_u
> +   riscv/virt
>
>  RISC-V CPU firmware
>  -------------------
> --
> 2.25.1
>
>