Re: [Qemu-devel] [PATCH 08/10] qxl: add vgamem_size_mb and vgamem_size

[Gerd Hoffmann <kraxel@redhat.com>]

On 06/12/12 11:37, Daniel P. Berrange wrote:
> On Tue, Jun 12, 2012 at 09:51:12AM +0200, Gerd Hoffmann wrote:
>> From: Alon Levy <alevy@redhat.com>
>>
>> In preperation for supporting a larger framebuffer for multiple monitors
>> on a single card, add a property to qxl vgamem_size_mb, and corresponding
>> byte sized vgamem_size, and use instead of VGA_RAM_SIZE.
> 
> How is this new property different from the existing 'vram_size' property
> we can set for QXL ?
> 
>>          DEFINE_PROP_UINT32("ram_size_mb",  PCIQXLDevice, ram_size_mb, -1),
>>          DEFINE_PROP_UINT32("vram_size_mb", PCIQXLDevice, vram32_size_mb, -1),
>>          DEFINE_PROP_UINT32("vram64_size_mb", PCIQXLDevice, vram_size_mb, -1),
>> +        DEFINE_PROP_UINT32("vgamem_mb", PCIQXLDevice, vgamem_size_mb, 8),
>>          DEFINE_PROP_END_OF_LIST(),
> 
> Or indeed, can you describe the semantics of each of the different
> ram size parameters here ?

Documenting this being a good idea just came across my mind these days
too.  Ok here we go (should probably cut+paste to docs/qxl.txt):

The qxl device has two large memory regions:

Region #1 is called "ram" and is mapped to PCI bar 0.  This is again
splitted into three parts:  The framebuffer at the start, the command
rings at the end, and storage area for spice rendering commands and
image data inbetween.

Region #2 is called "vram".  This is storage for images, called
"surfaces" in spice.  Surfaces can be both source and target for spice
rendering operations.  X11 can store offscreen pixmaps there for
example.  Once qxl gets 3D support surfaces can also be used for textures.

Now for the properties:

vgamem_mb
  specifies the size of the framebuffer portion of the "ram" region, in
  megabytes.  Must be big enougth to hold the maximum display
  resolution you want to use.  Replaces the fixed VGA_RAM_SIZE define.
  Default is 8 or 16 MB depending on machine type with all patches of
  this series applied (see last patch).

ram_size_mb
  specifies the total size of the "ram" region, in megabytes.  Defaults
  to 64 MB.  Must be larger than vgamem_mb obviously.

vram_size_mb
  specifies the total size of the "vram" region, in megabytes.
  Defaults to 64 MB.

vram64_size_mb
  if this one is present and larger than vram_size_mb qxl will get an
  additional 64bit pci bar.  Both 32bit and 64bit vram pci bars are
  backed by the "vram" memory region, the 32bit bar is an alias mapping
  for the first part of the 64bit pci bar.  This can be used to give
  guests *lots* of vram without exhausting 32bit pci address space.
  Obviously only useful for 64bit guests.  Requires cutting edge
  seabios to get the 64bit bar actually mapped above 4G.

ram_size
  specifies the total size of the "ram" region, in bytes.  For
  compatibility with older qemu versions, ignored if ram_size_mb
  property is present.

vram_size
  specifies the total size of the "vram" region, in bytes.  For
  compatibility with older qemu versions, ignored if vram_size_mb
  property is present.

cheers,
  Gerd