diff --git a/docs/system/riscv/sifive_u.rst b/docs/system/riscv/sifive_u.rst index dcdfbda931..32d0a1b85d 100644 --- a/docs/system/riscv/sifive_u.rst +++ b/docs/system/riscv/sifive_u.rst @@ -36,12 +36,21 @@ Hardware configuration information ---------------------------------- The ``sifive_u`` machine automatically generates a device tree blob ("dtb") -which it passes to the guest. 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 instead of using a DTB for the real hardware, as some of the devices are -not modeled by QEMU and trying to access these devices may cause unexpected -behavior. +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 instead of using a DTB for the real +hardware, as some of the devices are not modeled by QEMU and trying to access +these devices may cause unexpected behavior. + +If users want to provide their own DTB, they can use the ``-dtb`` option. +These DTBs should have the following requirements: + +* The /cpus node should contain at least one subnode for E51 and the number + of subnodes 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 ------------ @@ -122,6 +131,32 @@ To boot the newly built Linux kernel in QEMU with the ``sifive_u`` machine: -initrd /path/to/rootfs.ext4 \ -append "root=/dev/ram" +Alternatively, we can use a custom DTB to boot the machine by inserting a CLINT +node in fu540-c000.dtsi in the Linux kernel, + +.. code-block:: none + + clint: clint@2000000 { + compatible = "riscv,clint0"; + interrupts-extended = <&cpu0_intc 3 &cpu0_intc 7 + &cpu1_intc 3 &cpu1_intc 7 + &cpu2_intc 3 &cpu2_intc 7 + &cpu3_intc 3 &cpu3_intc 7 + &cpu4_intc 3 &cpu4_intc 7>; + reg = <0x00 0x2000000 0x00 0x10000>; + }; + +with the following command line options: + +.. code-block:: bash + + $ qemu-system-riscv64 -M sifive_u -smp 5 -m 8G \ + -display none -serial stdio \ + -kernel arch/riscv/boot/Image \ + -dtb arch/riscv/boot/dts/sifive/hifive-unleashed-a00.dtb \ + -initrd /path/to/rootfs.ext4 \ + -append "root=/dev/ram" + To build a Linux mainline kernel that can be booted by the ``sifive_u`` machine in 32-bit mode, use the rv32_defconfig configuration. A patch is required to fix the 32-bit boot issue for Linux kernel v5.10.