[PATCH v2 14/16] board: emulation: Add qemu-loongarch

[Simon Glass]

Hi Yao,

On 2026-07-01T11:17:53, Yao Zi <me at ziyao.cc> wrote:
> board: emulation: Add qemu-loongarch
>
> Yet another generic QEMU VIRT machine.
> QEMU placed FDT in memory before launching U-Boot, so we
> can just obtian FDT here.
>
> Signed-off-by: Jiaxun Yang <jiaxun.yang at flygoat.com>
> Signed-off-by: Yao Zi <me at ziyao.cc>
>
> arch/loongarch/Kconfig                            |  5 ++
>  arch/loongarch/dts/qemu-loongarch64.dts           |  9 +++
>  board/emulation/qemu-loongarch/Kconfig            | 68 +++++++++++++++++++++++
>  board/emulation/qemu-loongarch/MAINTAINERS        |  7 +++
>  board/emulation/qemu-loongarch/Makefile           |  6 ++
>  board/emulation/qemu-loongarch/qemu-loongarch.c   | 67 ++++++++++++++++++++++
>  board/emulation/qemu-loongarch/qemu-loongarch.env |  6 ++
>  configs/qemu-loongarch64_defconfig                | 36 ++++++++++++
>  include/configs/qemu-loongarch.h                  | 13 +++++
>  9 files changed, 217 insertions(+)

> Yet another generic QEMU VIRT machine.
> QEMU placed FDT in memory before launching U-Boot, so we
> can just obtian FDT here.

Please flesh this out a bit more - how the board is booted,
memory-layout assumptions, the FDT source. Also 'obtian' -> 'obtain'
and use present tense ('QEMU places the FDT ...').

> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
> @@ -7,9 +7,14 @@ config SYS_ARCH
>  choice
>       prompt "Target select"
>
> +config TARGET_QEMU_LOONGARCH_VIRT
> +     bool "Support QEMU Virt Board"
> +     select BOARD_LATE_INIT
> +
>  endchoice

Please move this symbol into board/emulation/qemu-loongarch/Kconfig
alongside the other options, so the arch Kconfig only lists the
choice. Also BOARD_LATE_INIT is duplicated as an 'imply' inside
BOARD_SPECIFIC_OPTIONS - pick one.

> diff --git a/board/emulation/qemu-loongarch/qemu-loongarch.c b/board/emulation/qemu-loongarch/qemu-loongarch.c
> @@ -0,0 +1,67 @@
> +phys_addr_t board_get_usable_ram_top(phys_size_t total_size)
> +{
> +     /* Limit RAM used by U-Boot to the DDR low region */
> +     if (gd->ram_top > 0x10000000)
> +             return 0x10000000;
> +
> +     return gd->ram_top;
> +}

Please introduce a named constant for 0x10000000 (something like
SYS_LOWMEM_TOP), and explain in the comment why the low region
matters - TLB/direct-map restriction, or a QEMU quirk?

> diff --git a/board/emulation/qemu-loongarch/qemu-loongarch.c b/board/emulation/qemu-loongarch/qemu-loongarch.c
> @@ -0,0 +1,67 @@
> +int board_init(void)
> +{
> +     return 0;
> +}

If there is nothing to do, please drop in favour of the weak default.

> diff --git a/board/emulation/qemu-loongarch/qemu-loongarch.c b/board/emulation/qemu-loongarch/qemu-loongarch.c
> @@ -0,0 +1,67 @@
> +int board_fdt_blob_setup(void **fdtp)
> +{
> +     /* Stored the DTB address there during our init */
> +     *fdtp = (void *)(ulong)0x100000;
> +     return 0;
> +}

The comment is misleading - U-Boot does not store the DTB anywhere;
QEMU (LoongArchQemuPkg) places it at this address. Please rework
the comment, and use a named constant rather than 0x100000. It
would also be worth an fdt_check_header() before returning success,
so a mis-launch fails cleanly.

> diff --git a/board/emulation/qemu-loongarch/qemu-loongarch.env b/board/emulation/qemu-loongarch/qemu-loongarch.env
> @@ -0,0 +1,6 @@
> +
> +stdin=serial,usbkbd
> +stdout=serial,vidconsole
> +stderr=serial,vidconsole

Drop the leading blank line.

> diff --git a/include/configs/qemu-loongarch.h b/include/configs/qemu-loongarch.h
> @@ -0,0 +1,13 @@
> +/* Those values are chosen by LoongArchQemuPkg */
> +#define CFG_SYS_INIT_RAM_ADDR        0x10000
> +#define CFG_SYS_INIT_RAM_SIZE        0x10000

'These values', not 'Those'. Also, since both the DTB address
(0x100000) and the low-RAM cap (0x10000000) are baked into the C
file, please pull those into this header so the QEMU/edk2 ABI lives
in one place.

Regards,
Simon