[libvirt] [PATCH v2 0/4] use the 'vram' attribute for QEMU video devices

[Gerd Hoffmann]

  Hi,

> The 'vgamem_mb' parameter for QXL sets the VGA framebuffer size, but the VGA
> mode in QXL is used only as fallback if the OS doesn't have any QXL drivers
> or before the drivers are loaded. The VGA framebuffer is part of the first ram
> for QXL and for that we have 'ram' attribute. The rest of the first ram is
> memory for rendering commands and it's data. Default VGA framebuffer size is
> 8MB which is sufficient.

It isn't that simple.   The vga framebuffer can be used as as video
memory in non-vga mode too.  Guest driver can choose whenever it uses
the vga framebuffer or vram bar.

Traditional behavior is to use the vga framebuffer, in fact very old qxl
device revisions don't have a vram pci bar in the first place.  Because
of that vgamem_mb should be configurable on qxl too.

cheers,
  Gerd