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docs/system/riscv: sifive_u: Document '-dtb' usage 

Update the 'sifive_u' machine documentation to mention the '-dtb'
option that can be used to pass a custom DTB to QEMU.

Signed-off-by: Bin Meng <bin.meng@windriver.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-id: 20210430071302.1489082-6-bmeng.cn@gmail.com
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
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Bin Meng 2021-04-30 15:13:00 +08:00 committed by Alistair Francis
parent 3ede8967c8
commit 0147af69ab
1 changed files with 41 additions and 6 deletions
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47
docs/system/riscv/sifive_u.rst
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@ -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.