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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 help8of the BIOS, and use this as framebuffer device /dev/fb0, like the m68k9(and other) ports do.10 11This means we decide at boot time whenever we want to run in text or12graphics mode. Switching mode later on (in protected mode) is13impossible; BIOS calls work in real mode only. VESA BIOS Extensions14Version 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 X1121 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. Read33Documentation/admin-guide/svga.rst for details.34 35You should compile in both vgacon (for text mode) and vesafb (for36graphics mode). Which of them takes over the console depends on37whenever the specified mode is text or graphics.38 39The graphic modes are NOT in the list which you get if you boot with40vga=ask and hit return. The mode you wish to use is derived from the41VESA mode number. Here are those VESA mode numbers:42 43====== ======= ======= ======== =========44colors 640x480 800x600 1024x768 1280x102445====== ======= ======= ======== =========46256 0x101 0x103 0x105 0x1074732k 0x110 0x113 0x116 0x1194864k 0x111 0x114 0x117 0x11A4916M 0x112 0x115 0x118 0x11B50====== ======= ======= ======== =========51 52 53The video mode number of the Linux kernel is the VESA mode number plus540x200:55 56 Linux_kernel_mode_number = VESA_mode_number + 0x20057 58So the table for the Kernel mode numbers are:59 60====== ======= ======= ======== =========61colors 640x480 800x600 1024x768 1280x102462====== ======= ======= ======== =========63256 0x301 0x303 0x305 0x3076432k 0x310 0x313 0x316 0x3196564k 0x311 0x314 0x317 0x31A6616M 0x312 0x315 0x318 0x31B67====== ======= ======= ======== =========68 69To enable one of those modes you have to specify "vga=ask" in the70lilo.conf file and rerun LILO. Then you can type in the desired71mode at the "vga=ask" prompt. For example if you like to use721024x768x256 colors you have to say "305" at this prompt.73 74If this does not work, this might be because your BIOS does not support75linear 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 BIOS77Extensions v2.0 are required, 1.2 is NOT sufficient. You will get a78"bad mode number" message if something goes wrong.79 801. Note: LILO cannot handle hex, for booting directly with81 "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 85X1186===87 88XF68_FBDev should work just fine, but it is non-accelerated. Running89another (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 up93with a broken console (and vesafb cannot do anything about this).94 95 96Refresh rates97=============98 99There is no way to change the vesafb video mode and/or timings after100booting linux. If you are not happy with the 60 Hz refresh rate, you101have these options:102 103 * configure and load the DOS-Tools for the graphics board (if104 available) and boot linux with loadlin.105 * use a native driver (matroxfb/atyfb) instead if vesafb. If none106 is available, write a new one!107 * VBE 3.0 might work too. I have neither a gfx board with VBE 3.0108 support nor the specs, so I have not checked this yet.109 110 111Configuration112=============113 114The VESA BIOS provides protected mode interface for changing115some parameters. vesafb can use it for palette changes and116to pan the display. It is turned off by default because it117seems not to work with some BIOS versions, but there are options118to turn it on.119 120You can pass options to vesafb using "video=vesafb:option" on121the kernel command line. Multiple options should be separated122by comma, like this: "video=vesafb:ypan,inverse"123 124Accepted options:125 126inverse use inverse color map127 128========= ======================================================================129ypan enable display panning using the VESA protected mode130 interface. The visible screen is just a window of the131 video memory, console scrolling is done by changing the132 start of the window.133 134 pro:135 136 * scrolling (fullscreen) is fast, because there is137 no need to copy around data.138 139 kontra:140 141 * scrolling only parts of the screen causes some142 ugly flicker effects (boot logo flickers for143 example).144 145ywrap Same as ypan, but assumes your gfx board can wrap-around146 the video memory (i.e. starts reading from top if it147 reaches the end of video memory). Faster than ypan.148 149redraw Scroll by redrawing the affected part of the screen, this150 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 framebuffer158 where n:159 160 - 0 - disabled (equivalent to nomtrr) (default)161 - 1 - uncachable162 - 2 - write-back163 - 3 - write-combining164 - 4 - write-through165 166 If you see the following in dmesg, choose the type that matches the167 old one. In this example, use "mtrr:2".168...169mtrr: type mismatch for e0000000,8000000 old: write-back new:170 write-combining171...172 173nomtrr disable mtrr174 175vremap:n176 Remap 'n' MiB of video RAM. If 0 or not specified, remap memory177 according to video mode. (2.5.66 patch/idea by Antonino Daplas178 reversed to give override possibility (allocate more fb memory179 than the kernel would) to 2.4 by tmb@iki.fi)180 181vtotal:n If the video BIOS of your card incorrectly determines the total182 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) changes190by Nico Schmoigl <schmoigl@rumms.uni-mannheim.de>191