[PATCH 1/1] doc: describe QEMU VGA emulation

[Simon Glass]

Hi Heinrich,

On Wed, 31 Dec 2025 at 06:44, Heinrich Schuchardt
<heinrich.schuchardt at canonical.com> wrote:
>
> Describe how the QEMU defconfigs can be used with an emulated GPU.
>
> Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt at canonical.com>
> ---
>  doc/board/emulation/index.rst |  1 +
>  doc/board/emulation/video.rst | 63 +++++++++++++++++++++++++++++++++++
>  2 files changed, 64 insertions(+)
>  create mode 100644 doc/board/emulation/video.rst

Reviewed-by: Simon Glass <simon.glass at canonical.com>

>
> diff --git a/doc/board/emulation/index.rst b/doc/board/emulation/index.rst
> index f8908166276..bda2240725f 100644
> --- a/doc/board/emulation/index.rst
> +++ b/doc/board/emulation/index.rst
> @@ -15,6 +15,7 @@ Emulation
>     qemu-sbsa
>     qemu-x86
>     qemu-xtensa
> +   video
>
>  Also see
>
> diff --git a/doc/board/emulation/video.rst b/doc/board/emulation/video.rst
> new file mode 100644
> index 00000000000..4943dcabeab
> --- /dev/null
> +++ b/doc/board/emulation/video.rst
> @@ -0,0 +1,63 @@
> +.. SPDX-License-Identifier: GPL-2.0-or-later
> +
> +Emulation of a graphics adapter
> +===============================
> +
> +Currently QEMU's ``bochs-display`` is the only emulated GPU that U-Boot's
> +generic QEMU defconfigs support. It emulates a PCIe connected graphics card

PCIe-connected

> +with VESA 2.0 VBE extensions.
> +
> +The following parameters can be specified.
> +
> +edid
> +    controls if EDID information is available. Allowable values are ``off`` and
> +    ``on``. The default is on.
> +
> +vgamem
> +    specifies the display memory size. The default value is 16 MiB.
> +    For UHD resolution 32 MiB is required.
> +
> +The following configuration parameters are relevant:
> +
> +CONFIG_VIDEO_BOCHS
> +    enable support for the Bochs GPU.
> +
> +CONFIG_VIDEO_BOCHS_SIZE_X
> +    defines the display width.
> +
> +CONFIG_VIDEO_BOCHS_SIZE_Y
> +    defines isplay height.

display

> +
> +CONFIG_VIDEO_PCI_DEFAULT_FB_SIZE
> +    sets the framebuffer size that QEMU can use for a device driver that is
> +    enabled after relocation. This should be chosed as

chosen

> +
> +    .. code-block::
> +
> +        CONFIG_VIDEO_PCI_DEFAULT_FB_SIZE >=
> +       4 * CONFIG_VIDEO_BOCHS_SIZE_X * CONFIG_VIDEO_BOCHS_SIZE_Y
> +
> +Here is an example QEMU invocation for qemu-riscv64_smode_defconfig:
> +
> +.. code-block:: bash
> +
> +    qemu-system-riscv64 \
> +      -M virt \
> +      -device bochs-display,vgamem=33554432 \
> +      -serial mon:stdio \
> +      -device qemu-xhci \
> +      -device usb-kbd \
> +      -kernel u-boot
> +
> +``mon:stdio`` provides a serial console. ``qemu-xhci`` a USB root hub.
> +``usb-kbd`` a USB keyboard.
> +
> +To start QEMU without GPU emulation use parameter ``-nographic`` like in the
> +following example.
> +
> +.. code-block:: bash
> +
> +    qemu-system-riscv64 \
> +      -M virt \
> +      -nographic \
> +      -kernel u-boot
> --
> 2.51.0
>

The Concept tree has build-qemu which handles these details. I wonder
if those scripts could be put into the extra repo Tom created?

Regards,
Simon