linux/Documentation/fb/efifb.rst
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   1==============
   2What is efifb?
   3==============
   4
   5This is a generic EFI platform driver for systems with UEFI firmware. The
   6system must be booted via the EFI stub for this to be usable. efifb supports
   7both firmware with Graphics Output Protocol (GOP) displays as well as older
   8systems with only Universal Graphics Adapter (UGA) displays.
   9
  10Supported Hardware
  11==================
  12
  13- iMac 17"/20"
  14- Macbook
  15- Macbook Pro 15"/17"
  16- MacMini
  17- ARM/ARM64/X86 systems with UEFI firmware
  18
  19How to use it?
  20==============
  21
  22For UGA displays, efifb does not have any kind of autodetection of your
  23machine.
  24
  25You have to add the following kernel parameters in your elilo.conf::
  26
  27        Macbook :
  28                video=efifb:macbook
  29        MacMini :
  30                video=efifb:mini
  31        Macbook Pro 15", iMac 17" :
  32                video=efifb:i17
  33        Macbook Pro 17", iMac 20" :
  34                video=efifb:i20
  35
  36For GOP displays, efifb can autodetect the display's resolution and framebuffer
  37address, so these should work out of the box without any special parameters.
  38
  39Accepted options:
  40
  41======= ===========================================================
  42nowc    Don't map the framebuffer write combined. This can be used
  43        to workaround side-effects and slowdowns on other CPU cores
  44        when large amounts of console data are written.
  45======= ===========================================================
  46
  47Options for GOP displays:
  48
  49mode=n
  50        The EFI stub will set the mode of the display to mode number n if
  51        possible.
  52
  53<xres>x<yres>[-(rgb|bgr|<bpp>)]
  54        The EFI stub will search for a display mode that matches the specified
  55        horizontal and vertical resolution, and optionally bit depth, and set
  56        the mode of the display to it if one is found. The bit depth can either
  57        "rgb" or "bgr" to match specifically those pixel formats, or a number
  58        for a mode with matching bits per pixel.
  59
  60auto
  61        The EFI stub will choose the mode with the highest resolution (product
  62        of horizontal and vertical resolution). If there are multiple modes
  63        with the highest resolution, it will choose one with the highest color
  64        depth.
  65
  66list
  67        The EFI stub will list out all the display modes that are available. A
  68        specific mode can then be chosen using one of the above options for the
  69        next boot.
  70
  71Edgar Hucek <gimli@dark-green.com>
  72