• Michal Januszewski's avatar
    uvesafb: the driver core · 8bdb3a2d
    Michal Januszewski authored
    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: default avatarMichal Januszewski <spock@gentoo.org>
    Signed-off-by: default avatarAntonino Daplas <adaplas@gmail.com>
    Cc: Paul Mundt <lethal@linux-sh.org>
    Cc: Paulo Marques <pmarques@grupopie.com>
    Cc: "H. Peter Anvin" <hpa@zytor.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    8bdb3a2d
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