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diff --git a/docs/system/riscv/virt.rst b/docs/system/riscv/virt.rst new file mode 100644 index 00000000..4b16e41d --- /dev/null +++ b/docs/system/riscv/virt.rst @@ -0,0 +1,189 @@ +'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 + +The hypervisor extension has been enabled for the default CPU, so virtual +machines with hypervisor extension can simply be used without explicitly +declaring. + +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. + +Machine-specific options +------------------------ + +The following machine-specific options are supported: + +- aclint=[on|off] + + When this option is "on", ACLINT devices will be emulated instead of + SiFive CLINT. When not specified, this option is assumed to be "off". + +- aia=[none|aplic|aplic-imsic] + + This option allows selecting interrupt controller defined by the AIA + (advanced interrupt architecture) specification. The "aia=aplic" selects + APLIC (advanced platform level interrupt controller) to handle wired + interrupts whereas the "aia=aplic-imsic" selects APLIC and IMSIC (incoming + message signaled interrupt controller) to handle both wired interrupts and + MSIs. When not specified, this option is assumed to be "none" which selects + SiFive PLIC to handle wired interrupts. + +- aia-guests=nnn + + The number of per-HART VS-level AIA IMSIC pages to be emulated for a guest + having AIA IMSIC (i.e. "aia=aplic-imsic" selected). When not specified, + the default number of per-HART VS-level AIA IMSIC pages is 0. + +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. + +Enabling TPM +------------ + +A TPM device can be connected to the virt board by following the steps below. + +First launch the TPM emulator: + +.. code-block:: bash + + $ swtpm socket --tpm2 -t -d --tpmstate dir=/tmp/tpm \ + --ctrl type=unixio,path=swtpm-sock + +Then launch QEMU with some additional arguments to link a TPM device to the backend: + +.. code-block:: bash + + $ qemu-system-riscv64 \ + ... other args .... \ + -chardev socket,id=chrtpm,path=swtpm-sock \ + -tpmdev emulator,id=tpm0,chardev=chrtpm \ + -device tpm-tis-device,tpmdev=tpm0 + +The TPM device can be seen in the memory tree and the generated device +tree and should be accessible from the guest software. |