Re: Any plan for command line '-g' option (graphical resolution and depth)?

[Mark Cave-Ayland]

On 20/02/2025 09:20, Philippe Mathieu-Daudé wrote:

> Hi,
>
> QEMU provides the global '-g' CLI option:
>
> $ qemu-system-foo --help
>
>    -g WxH[xDEPTH]  Set the initial graphical resolution and depth
>
> This option is used to pass resolution/depth information to guest
> firmwares in the machines defined in the following files:
>
>    hw/ppc/mac_newworld.c
>    hw/ppc/mac_oldworld.c
>    hw/ppc/prep.c
>    hw/ppc/spapr.c
>    hw/sparc/sun4m.c
>    hw/sparc64/sun4u.c
>
> Examples:
>
> - hw/ppc/spapr.c:1102:
>
>    _FDT(fdt_setprop_cell(fdt, c, "qemu,graphic-width", graphic_width));
>
> - hw/sparc64/sun4u.c:716:
>
>    fw_cfg_add_i16(fw_cfg, FW_CFG_SPARC64_WIDTH, graphic_width);
>
>
> Obviously we have default values, which are different per architecture!
> Clearly these ought to be machine properties.

At least for VGA it is possible to use VGA via the width and height properties to set 
the initial values i.e. on the command line with -device VGA,width=1024,height=768 
and then use an EDID parser to get the information in the firmware. But then we hit 
the same problem of how to set these properties from the command line on in-built 
devices again.

> It is also used to set TYPE_NUBUS_MACFB properties in hw/m68k/q800.c.
> Here i suppose we could directly use '-global nubus-macfb.width=value'
> etc. although I'm not sure it is the recommended way.

This approach should work, however -global feels more like a big hammer as opposed to 
a proper solution. In particular it doesn't work if you have e.g. multiple screens 
that you want set to different resolutions.

> Should we start deprecating '-g' as a whole?

I think there should be a better way to consolidate the default resolution selection 
on display devices (particularly in the case of multiple displays), so yes.


ATB,

Mark.