vesafb.rst (6667B)
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>