xref: /openbmc/linux/Documentation/fb/efifb.rst (revision 2fa5ebe3) 
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