vga: add specs for standard vga

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>

1 files changed, 64 insertions, 0 deletions

diff --git a/docs/specs/standard-vga.txt b/docs/specs/standard-vga.txt
new file mode 100644
index 0000000000..1cecccd469
--- /dev/null
+++ b/docs/specs/standard-vga.txt
@@ -0,0 +1,64 @@
+
+QEMU Standard VGA
+=================
+
+Exists in two variants, for isa and pci.
+
+command line switches:
+    -vga std            [ picks isa for -M isapc, otherwise pci ]
+    -device VGA         [ pci variant ]
+    -device isa-vga     [ isa variant ]
+
+
+PCI spec
+--------
+
+Applies to the pci variant only for obvious reasons.
+
+PCI ID: 1234:1111
+
+PCI Region 0:
+   Framebuffer memory, 16 MB in size (by default).
+   Size is tunable via vga_mem_mb property.
+
+PCI Region 1:
+   Reserved (so we have the option to make the framebuffer bar 64bit).
+
+PCI Region 2:
+   MMIO bar, 4096 bytes in size (qemu 1.3+)
+
+PCI ROM Region:
+   Holds the vgabios (qemu 0.14+).
+
+
+IO ports used
+-------------
+
+03c0 - 03df : standard vga ports
+01ce        : bochs vbe interface index port
+01cf        : bochs vbe interface data port
+
+
+Memory regions used
+-------------------
+
+0xe0000000 : Framebuffer memory, isa variant only.
+
+The pci variant used to mirror the framebuffer bar here, qemu 0.14+
+stops doing that (except when in -M pc-$old compat mode).
+
+
+MMIO area spec
+--------------
+
+Likewise applies to the pci variant only for obvious reasons.
+
+0000 - 03ff : reserved, for possible virtio extension.
+0400 - 041f : vga ioports (0x3c0 -> 0x3df), remapped 1:1.
+              word access is supported, bytes are written
+              in little endia order (aka index port first),
+              so indexed registers can be updated with a
+              single mmio write (and thus only one vmexit).
+0500 - 0515 : bochs dispi interface registers, mapped flat
+              without index/data ports.  Use (index << 1)
+              as offset for (16bit) register access.