linux/Documentation/fb/vesafb.rst
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   1===============
   2What is vesafb?
   3===============
   4
   5This is a generic driver for a graphic framebuffer on intel boxes.
   6
   7The idea is simple:  Turn on graphics mode at boot time with the help
   8of the BIOS, and use this as framebuffer device /dev/fb0, like the m68k
   9(and other) ports do.
  10
  11This means we decide at boot time whenever we want to run in text or
  12graphics mode.  Switching mode later on (in protected mode) is
  13impossible; BIOS calls work in real mode only.  VESA BIOS Extensions
  14Version 2.0 are required, because we need a linear frame buffer.
  15
  16Advantages:
  17
  18 * It provides a nice large console (128 cols + 48 lines with 1024x768)
  19   without using tiny, unreadable fonts.
  20 * You can run XF68_FBDev on top of /dev/fb0 (=> non-accelerated X11
  21   support for every VBE 2.0 compliant graphics board).
  22 * Most important: boot logo :-)
  23
  24Disadvantages:
  25
  26 * graphic mode is slower than text mode...
  27
  28
  29How to use it?
  30==============
  31
  32Switching modes is done using the vga=... boot parameter.  Read
  33Documentation/admin-guide/svga.rst for details.
  34
  35You should compile in both vgacon (for text mode) and vesafb (for
  36graphics mode). Which of them takes over the console depends on
  37whenever the specified mode is text or graphics.
  38
  39The graphic modes are NOT in the list which you get if you boot with
  40vga=ask and hit return. The mode you wish to use is derived from the
  41VESA mode number. Here are those VESA mode numbers:
  42
  43====== =======  =======  ======== =========
  44colors 640x480  800x600  1024x768 1280x1024
  45====== =======  =======  ======== =========
  46256    0x101    0x103    0x105    0x107
  4732k    0x110    0x113    0x116    0x119
  4864k    0x111    0x114    0x117    0x11A
  4916M    0x112    0x115    0x118    0x11B
  50====== =======  =======  ======== =========
  51
  52
  53The video mode number of the Linux kernel is the VESA mode number plus
  540x200:
  55
  56 Linux_kernel_mode_number = VESA_mode_number + 0x200
  57
  58So the table for the Kernel mode numbers are:
  59
  60====== =======  =======  ======== =========
  61colors 640x480  800x600  1024x768 1280x1024
  62====== =======  =======  ======== =========
  63256    0x301    0x303    0x305    0x307
  6432k    0x310    0x313    0x316    0x319
  6564k    0x311    0x314    0x317    0x31A
  6616M    0x312    0x315    0x318    0x31B
  67====== =======  =======  ======== =========
  68
  69To enable one of those modes you have to specify "vga=ask" in the
  70lilo.conf file and rerun LILO. Then you can type in the desired
  71mode at the "vga=ask" prompt. For example if you like to use
  721024x768x256 colors you have to say "305" at this prompt.
  73
  74If this does not work, this might be because your BIOS does not support
  75linear framebuffers or because it does not support this mode at all.
  76Even if your board does, it might be the BIOS which does not.  VESA BIOS
  77Extensions v2.0 are required, 1.2 is NOT sufficient.  You will get a
  78"bad mode number" message if something goes wrong.
  79
  801. Note: LILO cannot handle hex, for booting directly with
  81   "vga=mode-number" you have to transform the numbers to decimal.
  822. Note: Some newer versions of LILO appear to work with those hex values,
  83   if you set the 0x in front of the numbers.
  84
  85X11
  86===
  87
  88XF68_FBDev should work just fine, but it is non-accelerated.  Running
  89another (accelerated) X-Server like XF86_SVGA might or might not work.
  90It depends on X-Server and graphics board.
  91
  92The X-Server must restore the video mode correctly, else you end up
  93with a broken console (and vesafb cannot do anything about this).
  94
  95
  96Refresh rates
  97=============
  98
  99There is no way to change the vesafb video mode and/or timings after
 100booting linux.  If you are not happy with the 60 Hz refresh rate, you
 101have these options:
 102
 103 * configure and load the DOS-Tools for the graphics board (if
 104   available) and boot linux with loadlin.
 105 * use a native driver (matroxfb/atyfb) instead if vesafb.  If none
 106   is available, write a new one!
 107 * VBE 3.0 might work too.  I have neither a gfx board with VBE 3.0
 108   support nor the specs, so I have not checked this yet.
 109
 110
 111Configuration
 112=============
 113
 114The VESA BIOS provides protected mode interface for changing
 115some parameters.  vesafb can use it for palette changes and
 116to pan the display.  It is turned off by default because it
 117seems not to work with some BIOS versions, but there are options
 118to turn it on.
 119
 120You can pass options to vesafb using "video=vesafb:option" on
 121the kernel command line.  Multiple options should be separated
 122by comma, like this: "video=vesafb:ypan,inverse"
 123
 124Accepted options:
 125
 126inverse use inverse color map
 127
 128========= ======================================================================
 129ypan      enable display panning using the VESA protected mode
 130          interface.  The visible screen is just a window of the
 131          video memory, console scrolling is done by changing the
 132          start of the window.
 133
 134          pro:
 135
 136                * scrolling (fullscreen) is fast, because there is
 137                  no need to copy around data.
 138
 139          kontra:
 140
 141                * scrolling only parts of the screen causes some
 142                  ugly flicker effects (boot logo flickers for
 143                  example).
 144
 145ywrap     Same as ypan, but assumes your gfx board can wrap-around
 146          the video memory (i.e. starts reading from top if it
 147          reaches the end of video memory).  Faster than ypan.
 148
 149redraw    Scroll by redrawing the affected part of the screen, this
 150          is the safe (and slow) default.
 151
 152
 153vgapal    Use the standard vga registers for palette changes.
 154          This is the default.
 155pmipal    Use the protected mode interface for palette changes.
 156
 157mtrr:n    Setup memory type range registers for the vesafb framebuffer
 158          where n:
 159
 160              - 0 - disabled (equivalent to nomtrr) (default)
 161              - 1 - uncachable
 162              - 2 - write-back
 163              - 3 - write-combining
 164              - 4 - write-through
 165
 166          If you see the following in dmesg, choose the type that matches the
 167          old one. In this example, use "mtrr:2".
 168...
 169mtrr:     type mismatch for e0000000,8000000 old: write-back new:
 170          write-combining
 171...
 172
 173nomtrr    disable mtrr
 174
 175vremap:n
 176          Remap 'n' MiB of video RAM. If 0 or not specified, remap memory
 177          according to video mode. (2.5.66 patch/idea by Antonino Daplas
 178          reversed to give override possibility (allocate more fb memory
 179          than the kernel would) to 2.4 by tmb@iki.fi)
 180
 181vtotal:n  If the video BIOS of your card incorrectly determines the total
 182          amount of video RAM, use this option to override the BIOS (in MiB).
 183========= ======================================================================
 184
 185Have fun!
 186
 187Gerd Knorr <kraxel@goldbach.in-berlin.de>
 188
 189Minor (mostly typo) changes
 190by Nico Schmoigl <schmoigl@rumms.uni-mannheim.de>
 191