[Buildroot] [PATCH 1/1] configs/qemu: add qemu_riscv64_virt_defconfig

[Mark Corbin <mark.corbin@embecosm.com>]

Hello Thomas

On 02/09/18 20:47, Thomas Petazzoni wrote:
> Hello Mark,
>
> On Fri, 31 Aug 2018 15:38:53 +0100, Mark Corbin wrote:
>> Add RISC-V 64-bit defconfig for QEMU virt machine.
>>
>> Tested with QEMU 2.12.1
> Here you say 2.12.1, in the readme.txt file you say 2.12.92. I assume
> one or the other has a typo :-)
Oops..typo on my part. I did test against both versions in fact, but
I'll stick with 2.12.1 as it is an official release.
>
>>  board/qemu/riscv64-virt/linux.config | 24 ++++++++++++++++++++++++
>>  board/qemu/riscv64-virt/readme.txt   | 22 ++++++++++++++++++++++
>>  configs/qemu_riscv64_virt_defconfig  | 24 ++++++++++++++++++++++++
>>  3 files changed, 70 insertions(+)
> Please add an entry in the DEVELOPERS file. When you will do a patch
> series with the base RISC-V support:
>
>  - The patch introducing the RISC-V support should add an entry in the
>    DEVELOPERS file for you, the arch/Config.in.riscv file and other
>    files introduced by this first patch.
>
>  - The patch introducing the RISC-V qemu defconfig should add more
>    items to the DEVELOPERS file entry, to list the files related to
>    this defconfig.
>
>> diff --git a/board/qemu/riscv64-virt/readme.txt b/board/qemu/riscv64-virt/readme.txt
>> new file mode 100644
>> index 0000000000..be563c969e
>> --- /dev/null
>> +++ b/board/qemu/riscv64-virt/readme.txt
>> @@ -0,0 +1,22 @@
>> +Run the emulation with:
>> +
>> +  qemu-system-riscv64 -M virt -kernel <path-to-bl>/bbl -append "root=/dev/vda ro console=ttyS0" -drive file=<path-to-buildroot>/output/images/rootfs.ext2,format=raw,id=hd0 -device virtio-blk-device,drive=hd0 -netdev user,id=net0 -device virtio-net-device,netdev=net0 -nographic
>> +
>> +The Buildroot generated vmlinux image will need to be combined with the Berkeley Boot Loader (BBL) as follows:
>> +
>> +  export RISCV=<path-to-buildroot>/output/host
>> +  export PATH=$PATH:$RISCV/bin
>> +  git clone https://github.com/riscv/riscv-pk
>> +  cd riscv-pk
>> +  mkdir build
>> +  cd build
>> +  ../configure \
>> +    --host=riscv64-buildroot-linux-gnu \
>> +    --with-payload=<path-to-buildroot>/output/images/vmlinux
>> +  make
> Then we want to create a package for the BBL, in boot/riscv-pk/. See
> boot/boot-wrapper-aarch64/ for an example of bootloader wraps the
> kernel image. It depends on the kernel build in Config.in:
>
> config BR2_TARGET_BOOT_WRAPPER_AARCH64
>         bool "boot-wrapper-aarch64"
>         depends on BR2_aarch64
>         depends on BR2_LINUX_KERNEL
>
> And then in the .mk file, we ensure the Linux kernel is built before:
>
> BOOT_WRAPPER_AARCH64_DEPENDENCIES = linux
>
> And we pass the path to the kernel tree (which it needs to get the
> kernel image):
>
> BOOT_WRAPPER_AARCH64_CONF_OPTS = \
>         --with-kernel-dir=$(LINUX_DIR) \

I had been reluctant to add riscv-pk to Buildroot as a bootloader, as I
see it as an interim solution until riscv support makes it into UBoot or
Barebox. On the other hand, riscv kernel images aren't much use without
it at the moment.

I do have a preliminary riscv-pk package working based on your helpful
pointers to boot-wrapper-aarch64. Do people prefer to add it as
'risc-pk' when it is only the Berkeley Boot Loader part that is
significant? I would have added it as 'bbl', but I can see the potential
confusion when the package/repository is 'riscv-pk'.

Regards

Mark

-- 
Mark Corbin
Embecosm Ltd.
https://www.embecosm.com