uvesafb is an enhanced version of vesafb. It uses a userspace helper (v86d)
to execute calls to the x86 Video BIOS functions. The driver is not limited
to any specific arch and whether it works on a given arch or not depends on
that arch being supported by the userspace daemon. It has been tested on
x86_32 and x86_64.

A single BIOS call is represented by an instance of the uvesafb_ktask
structure. This structure contains a buffer, a completion struct and a
uvesafb_task substructure, containing the values of the x86 registers, a flags
field and a field indicating the length of the buffer. Whenever a BIOS call
is made in the driver, uvesafb_exec() builds a message using the uvesafb_task
substructure and the contents of the buffer. This message is then assigned a
random ack number and sent to the userspace daemon using the connector
interface.

The message's sequence number is used as an index for the uvfb_tasks array,
which provides a mapping from the messages coming from userspace to the
in-kernel uvesafb_ktask structs.

The userspace daemon performs the requested operation and sends a reply in the
form of a uvesafb_task struct and, optionally, a buffer. The seq and ack
numbers in the reply should be exactly the same as those in the request.

Each message from userspace is processed by uvesafb_cn_callback() and after
passing a few sanity checks leads to the completion of a BIOS call request.

Signed-off-by: Michal Januszewski
Signed-off-by: Antonino Daplas
Cc: Paul Mundt
Cc: Paulo Marques
Cc: "H. Peter Anvin"
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds