6df743dc31
In rST markup, single backticks `like this` represent "interpreted text", which can be handled as a bunch of different things if tagged with a specific "role": https://docutils.sourceforge.io/docs/ref/rst/restructuredtext.html#interpreted-text (the most common one for us is "reference to a URL, which gets hyperlinked"). The default "role" if none is specified is "title_reference", intended for references to book or article titles, and it renders into the HTML as <cite>...</cite> (usually comes out as italics). This commit fixes various places in the manual which were using single backticks when double backticks (for literal text) were intended, and covers those files where only one or two instances of these errors were made. Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
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ReStructuredText
139 lines
4.9 KiB
ReStructuredText
'virt' Generic Virtual Platform (``virt``)
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==========================================
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The ``virt`` board is a platform which does not correspond to any real hardware;
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it is designed for use in virtual machines. It is the recommended board type
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if you simply want to run a guest such as Linux and do not care about
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reproducing the idiosyncrasies and limitations of a particular bit of
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real-world hardware.
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Supported devices
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-----------------
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The ``virt`` machine supports the following devices:
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* Up to 8 generic RV32GC/RV64GC cores, with optional extensions
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* Core Local Interruptor (CLINT)
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* Platform-Level Interrupt Controller (PLIC)
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* CFI parallel NOR flash memory
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* 1 NS16550 compatible UART
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* 1 Google Goldfish RTC
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* 1 SiFive Test device
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* 8 virtio-mmio transport devices
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* 1 generic PCIe host bridge
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* The fw_cfg device that allows a guest to obtain data from QEMU
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Note that the default CPU is a generic RV32GC/RV64GC. Optional extensions
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can be enabled via command line parameters, e.g.: ``-cpu rv64,x-h=true``
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enables the hypervisor extension for RV64.
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Hardware configuration information
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----------------------------------
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The ``virt`` machine automatically generates a device tree blob ("dtb")
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which it passes to the guest, if there is no ``-dtb`` option. This provides
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information about the addresses, interrupt lines and other configuration of
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the various devices in the system. Guest software should discover the devices
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that are present in the generated DTB.
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If users want to provide their own DTB, they can use the ``-dtb`` option.
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These DTBs should have the following requirements:
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* The number of subnodes of the /cpus node should match QEMU's ``-smp`` option
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* The /memory reg size should match QEMU’s selected ram_size via ``-m``
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* Should contain a node for the CLINT device with a compatible string
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"riscv,clint0" if using with OpenSBI BIOS images
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Boot options
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------------
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The ``virt`` machine can start using the standard -kernel functionality
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for loading a Linux kernel, a VxWorks kernel, an S-mode U-Boot bootloader
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with the default OpenSBI firmware image as the -bios. It also supports
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the recommended RISC-V bootflow: U-Boot SPL (M-mode) loads OpenSBI fw_dynamic
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firmware and U-Boot proper (S-mode), using the standard -bios functionality.
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Running Linux kernel
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--------------------
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Linux mainline v5.12 release is tested at the time of writing. To build a
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Linux mainline kernel that can be booted by the ``virt`` machine in
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64-bit mode, simply configure the kernel using the defconfig configuration:
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.. code-block:: bash
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$ export ARCH=riscv
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$ export CROSS_COMPILE=riscv64-linux-
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$ make defconfig
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$ make
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To boot the newly built Linux kernel in QEMU with the ``virt`` machine:
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.. code-block:: bash
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$ qemu-system-riscv64 -M virt -smp 4 -m 2G \
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-display none -serial stdio \
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-kernel arch/riscv/boot/Image \
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-initrd /path/to/rootfs.cpio \
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-append "root=/dev/ram"
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To build a Linux mainline kernel that can be booted by the ``virt`` machine
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in 32-bit mode, use the rv32_defconfig configuration. A patch is required to
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fix the 32-bit boot issue for Linux kernel v5.12.
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.. code-block:: bash
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$ export ARCH=riscv
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$ export CROSS_COMPILE=riscv64-linux-
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$ curl https://patchwork.kernel.org/project/linux-riscv/patch/20210627135117.28641-1-bmeng.cn@gmail.com/mbox/ > riscv.patch
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$ git am riscv.patch
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$ make rv32_defconfig
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$ make
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Replace ``qemu-system-riscv64`` with ``qemu-system-riscv32`` in the command
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line above to boot the 32-bit Linux kernel. A rootfs image containing 32-bit
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applications shall be used in order for kernel to boot to user space.
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Running U-Boot
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--------------
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U-Boot mainline v2021.04 release is tested at the time of writing. To build an
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S-mode U-Boot bootloader that can be booted by the ``virt`` machine, use
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the qemu-riscv64_smode_defconfig with similar commands as described above for Linux:
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.. code-block:: bash
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$ export CROSS_COMPILE=riscv64-linux-
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$ make qemu-riscv64_smode_defconfig
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Boot the 64-bit U-Boot S-mode image directly:
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.. code-block:: bash
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$ qemu-system-riscv64 -M virt -smp 4 -m 2G \
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-display none -serial stdio \
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-kernel /path/to/u-boot.bin
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To test booting U-Boot SPL which in M-mode, which in turn loads a FIT image
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that bundles OpenSBI fw_dynamic firmware and U-Boot proper (S-mode) together,
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build the U-Boot images using riscv64_spl_defconfig:
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.. code-block:: bash
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$ export CROSS_COMPILE=riscv64-linux-
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$ export OPENSBI=/path/to/opensbi-riscv64-generic-fw_dynamic.bin
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$ make qemu-riscv64_spl_defconfig
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The minimal QEMU commands to run U-Boot SPL are:
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.. code-block:: bash
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$ qemu-system-riscv64 -M virt -smp 4 -m 2G \
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-display none -serial stdio \
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-bios /path/to/u-boot-spl \
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-device loader,file=/path/to/u-boot.itb,addr=0x80200000
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To test 32-bit U-Boot images, switch to use qemu-riscv32_smode_defconfig and
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riscv32_spl_defconfig builds, and replace ``qemu-system-riscv64`` with
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``qemu-system-riscv32`` in the command lines above to boot the 32-bit U-Boot.
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