0001 ===============
0002 What is vesafb?
0003 ===============
0004
0005 This is a generic driver for a graphic framebuffer on intel boxes.
0006
0007 The idea is simple: Turn on graphics mode at boot time with the help
0008 of the BIOS, and use this as framebuffer device /dev/fb0, like the m68k
0009 (and other) ports do.
0010
0011 This means we decide at boot time whenever we want to run in text or
0012 graphics mode. Switching mode later on (in protected mode) is
0013 impossible; BIOS calls work in real mode only. VESA BIOS Extensions
0014 Version 2.0 are required, because we need a linear frame buffer.
0015
0016 Advantages:
0017
0018 * It provides a nice large console (128 cols + 48 lines with 1024x768)
0019 without using tiny, unreadable fonts.
0020 * You can run XF68_FBDev on top of /dev/fb0 (=> non-accelerated X11
0021 support for every VBE 2.0 compliant graphics board).
0022 * Most important: boot logo :-)
0023
0024 Disadvantages:
0025
0026 * graphic mode is slower than text mode...
0027
0028
0029 How to use it?
0030 ==============
0031
0032 Switching modes is done using the vga=... boot parameter. Read
0033 Documentation/admin-guide/svga.rst for details.
0034
0035 You should compile in both vgacon (for text mode) and vesafb (for
0036 graphics mode). Which of them takes over the console depends on
0037 whenever the specified mode is text or graphics.
0038
0039 The graphic modes are NOT in the list which you get if you boot with
0040 vga=ask and hit return. The mode you wish to use is derived from the
0041 VESA mode number. Here are those VESA mode numbers:
0042
0043 ====== ======= ======= ======== =========
0044 colors 640x480 800x600 1024x768 1280x1024
0045 ====== ======= ======= ======== =========
0046 256 0x101 0x103 0x105 0x107
0047 32k 0x110 0x113 0x116 0x119
0048 64k 0x111 0x114 0x117 0x11A
0049 16M 0x112 0x115 0x118 0x11B
0050 ====== ======= ======= ======== =========
0051
0052
0053 The video mode number of the Linux kernel is the VESA mode number plus
0054 0x200:
0055
0056 Linux_kernel_mode_number = VESA_mode_number + 0x200
0057
0058 So the table for the Kernel mode numbers are:
0059
0060 ====== ======= ======= ======== =========
0061 colors 640x480 800x600 1024x768 1280x1024
0062 ====== ======= ======= ======== =========
0063 256 0x301 0x303 0x305 0x307
0064 32k 0x310 0x313 0x316 0x319
0065 64k 0x311 0x314 0x317 0x31A
0066 16M 0x312 0x315 0x318 0x31B
0067 ====== ======= ======= ======== =========
0068
0069 To enable one of those modes you have to specify "vga=ask" in the
0070 lilo.conf file and rerun LILO. Then you can type in the desired
0071 mode at the "vga=ask" prompt. For example if you like to use
0072 1024x768x256 colors you have to say "305" at this prompt.
0073
0074 If this does not work, this might be because your BIOS does not support
0075 linear framebuffers or because it does not support this mode at all.
0076 Even if your board does, it might be the BIOS which does not. VESA BIOS
0077 Extensions v2.0 are required, 1.2 is NOT sufficient. You will get a
0078 "bad mode number" message if something goes wrong.
0079
0080 1. Note: LILO cannot handle hex, for booting directly with
0081 "vga=mode-number" you have to transform the numbers to decimal.
0082 2. Note: Some newer versions of LILO appear to work with those hex values,
0083 if you set the 0x in front of the numbers.
0084
0085 X11
0086 ===
0087
0088 XF68_FBDev should work just fine, but it is non-accelerated. Running
0089 another (accelerated) X-Server like XF86_SVGA might or might not work.
0090 It depends on X-Server and graphics board.
0091
0092 The X-Server must restore the video mode correctly, else you end up
0093 with a broken console (and vesafb cannot do anything about this).
0094
0095
0096 Refresh rates
0097 =============
0098
0099 There is no way to change the vesafb video mode and/or timings after
0100 booting linux. If you are not happy with the 60 Hz refresh rate, you
0101 have these options:
0102
0103 * configure and load the DOS-Tools for the graphics board (if
0104 available) and boot linux with loadlin.
0105 * use a native driver (matroxfb/atyfb) instead if vesafb. If none
0106 is available, write a new one!
0107 * VBE 3.0 might work too. I have neither a gfx board with VBE 3.0
0108 support nor the specs, so I have not checked this yet.
0109
0110
0111 Configuration
0112 =============
0113
0114 The VESA BIOS provides protected mode interface for changing
0115 some parameters. vesafb can use it for palette changes and
0116 to pan the display. It is turned off by default because it
0117 seems not to work with some BIOS versions, but there are options
0118 to turn it on.
0119
0120 You can pass options to vesafb using "video=vesafb:option" on
0121 the kernel command line. Multiple options should be separated
0122 by comma, like this: "video=vesafb:ypan,inverse"
0123
0124 Accepted options:
0125
0126 inverse use inverse color map
0127
0128 ========= ======================================================================
0129 ypan enable display panning using the VESA protected mode
0130 interface. The visible screen is just a window of the
0131 video memory, console scrolling is done by changing the
0132 start of the window.
0133
0134 pro:
0135
0136 * scrolling (fullscreen) is fast, because there is
0137 no need to copy around data.
0138
0139 kontra:
0140
0141 * scrolling only parts of the screen causes some
0142 ugly flicker effects (boot logo flickers for
0143 example).
0144
0145 ywrap Same as ypan, but assumes your gfx board can wrap-around
0146 the video memory (i.e. starts reading from top if it
0147 reaches the end of video memory). Faster than ypan.
0148
0149 redraw Scroll by redrawing the affected part of the screen, this
0150 is the safe (and slow) default.
0151
0152
0153 vgapal Use the standard vga registers for palette changes.
0154 This is the default.
0155 pmipal Use the protected mode interface for palette changes.
0156
0157 mtrr:n Setup memory type range registers for the vesafb framebuffer
0158 where n:
0159
0160 - 0 - disabled (equivalent to nomtrr) (default)
0161 - 1 - uncachable
0162 - 2 - write-back
0163 - 3 - write-combining
0164 - 4 - write-through
0165
0166 If you see the following in dmesg, choose the type that matches the
0167 old one. In this example, use "mtrr:2".
0168 ...
0169 mtrr: type mismatch for e0000000,8000000 old: write-back new:
0170 write-combining
0171 ...
0172
0173 nomtrr disable mtrr
0174
0175 vremap:n
0176 Remap 'n' MiB of video RAM. If 0 or not specified, remap memory
0177 according to video mode. (2.5.66 patch/idea by Antonino Daplas
0178 reversed to give override possibility (allocate more fb memory
0179 than the kernel would) to 2.4 by tmb@iki.fi)
0180
0181 vtotal:n If the video BIOS of your card incorrectly determines the total
0182 amount of video RAM, use this option to override the BIOS (in MiB).
0183 ========= ======================================================================
0184
0185 Have fun!
0186
0187 Gerd Knorr <kraxel@goldbach.in-berlin.de>
0188
0189 Minor (mostly typo) changes
0190 by Nico Schmoigl <schmoigl@rumms.uni-mannheim.de>
