A Virtual KMS Driver For QEMU Comes, Again

A virtual Cirrus KMS driver has once again appeared for providing kernel mode-setting support for virtualized guests using QEMU.

It was more than one year ago that a virtual Cirrus KMS driver was published by Red Hat's Matthew Garrett for use with QEMU/KVM virtualization, rather than just having the xf86-video-cirrus DDX driver to use. Back then the driver was working fairly well from my initial testing, but it never ended up being merged about or heard about again... Until today.

David Airlie has published an updated virtual Cirrus Linux KMS driver intended for use with QEMU. From the mailing list, "This is the initial driver for emulated cirrus GPU found in qemu. This driver only supports the emulated GPU and doesn't attempt to bind to any real cirrus GPUs. This driver is intended to be used with xf86-video-modesetting in userspace. This follow the same design as ast and mgag200, and is based on work done by Matthew Garrett previously. This GPU has no hw cursor, and it can't scanout 32-bpp, only packed 24-bpp. i.e. it sucks."

This virtual kernel mode-setting driver for the Linux kernel is just around 2,000 lines of code and will presumably be set for merging into the Linux 3.5 kernel. The xf86-video-cirrus isn't being adapted to handle the Cirrus DRM driver, but rather is intended to just work with the generic xf86-video-modesetting DDX.

This is just the latest basic KMS driver to be published by Red Hat. In recent weeks there's been a Matrox KMS driver and the AST KMS driver. After moving to ship DRI2-only drivers in Fedora 17, Red Hat is looking to ship KMS-only drivers in future versions of Red Hat Enterprise Linux.