Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 EST.
1 2 What is vesafb? 3 =============== 4 5 This is a generic driver for a graphic framebuffer on intel boxes. 6 7 The idea is simple: Turn on graphics mode at boot time with the help 8 of the BIOS, and use this as framebuffer device /dev/fb0, like the m68k 9 (and other) ports do. 10 11 This means we decide at boot time whenever we want to run in text or 12 graphics mode. Switching mode later on (in protected mode) is 13 impossible; BIOS calls work in real mode only. VESA BIOS Extensions 14 Version 2.0 are required, because we need a linear frame buffer. 15 16 Advantages: 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 24 Disadvantages: 25 26 * graphic mode is slower than text mode... 27 28 29 How to use it? 30 ============== 31 32 Switching modes is done using the vga=... boot parameter. Read 33 Documentation/svga.txt for details. 34 35 You should compile in both vgacon (for text mode) and vesafb (for 36 graphics mode). Which of them takes over the console depends on 37 whenever the specified mode is text or graphics. 38 39 The graphic modes are NOT in the list which you get if you boot with 40 vga=ask and hit return. The mode you wish to use is derived from the 41 VESA mode number. Here are those VESA mode numbers: 42 43 | 640x480 800x600 1024x768 1280x1024 44 ----+------------------------------------- 45 256 | 0x101 0x103 0x105 0x107 46 32k | 0x110 0x113 0x116 0x119 47 64k | 0x111 0x114 0x117 0x11A 48 16M | 0x112 0x115 0x118 0x11B 49 50 The video mode number of the Linux kernel is the VESA mode number plus 51 0x200. 52 53 Linux_kernel_mode_number = VESA_mode_number + 0x200 54 55 So the table for the Kernel mode numbers are: 56 57 | 640x480 800x600 1024x768 1280x1024 58 ----+------------------------------------- 59 256 | 0x301 0x303 0x305 0x307 60 32k | 0x310 0x313 0x316 0x319 61 64k | 0x311 0x314 0x317 0x31A 62 16M | 0x312 0x315 0x318 0x31B 63 64 To enable one of those modes you have to specify "vga=ask" in the 65 lilo.conf file and rerun LILO. Then you can type in the desired 66 mode at the "vga=ask" prompt. For example if you like to use 67 1024x768x256 colors you have to say "305" at this prompt. 68 69 If this does not work, this might be because your BIOS does not support 70 linear framebuffers or because it does not support this mode at all. 71 Even if your board does, it might be the BIOS which does not. VESA BIOS 72 Extensions v2.0 are required, 1.2 is NOT sufficient. You will get a 73 "bad mode number" message if something goes wrong. 74 75 1. Note: LILO cannot handle hex, for booting directly with 76 "vga=mode-number" you have to transform the numbers to decimal. 77 2. Note: Some newer versions of LILO appear to work with those hex values, 78 if you set the 0x in front of the numbers. 79 80 X11 81 === 82 83 XF68_FBDev should work just fine, but it is non-accelerated. Running 84 another (accelerated) X-Server like XF86_SVGA might or might not work. 85 It depends on X-Server and graphics board. 86 87 The X-Server must restore the video mode correctly, else you end up 88 with a broken console (and vesafb cannot do anything about this). 89 90 91 Refresh rates 92 ============= 93 94 There is no way to change the vesafb video mode and/or timings after 95 booting linux. If you are not happy with the 60 Hz refresh rate, you 96 have these options: 97 98 * configure and load the DOS-Tools for the graphics board (if 99 available) and boot linux with loadlin. 100 * use a native driver (matroxfb/atyfb) instead if vesafb. If none 101 is available, write a new one! 102 * VBE 3.0 might work too. I have neither a gfx board with VBE 3.0 103 support nor the specs, so I have not checked this yet. 104 105 106 Configuration 107 ============= 108 109 The VESA BIOS provides protected mode interface for changing 110 some parameters. vesafb can use it for palette changes and 111 to pan the display. It is turned off by default because it 112 seems not to work with some BIOS versions, but there are options 113 to turn it on. 114 115 You can pass options to vesafb using "video=vesafb:option" on 116 the kernel command line. Multiple options should be separated 117 by comma, like this: "video=vesafb:ypan,invers" 118 119 Accepted options: 120 121 invers no comment... 122 123 ypan enable display panning using the VESA protected mode 124 interface. The visible screen is just a window of the 125 video memory, console scrolling is done by changing the 126 start of the window. 127 pro: * scrolling (fullscreen) is fast, because there is 128 no need to copy around data. 129 * You'll get scrollback (the Shift-PgUp thing), 130 the video memory can be used as scrollback buffer 131 kontra: * scrolling only parts of the screen causes some 132 ugly flicker effects (boot logo flickers for 133 example). 134 135 ywrap Same as ypan, but assumes your gfx board can wrap-around 136 the video memory (i.e. starts reading from top if it 137 reaches the end of video memory). Faster than ypan. 138 139 redraw scroll by redrawing the affected part of the screen, this 140 is the safe (and slow) default. 141 142 143 vgapal Use the standard vga registers for palette changes. 144 This is the default. 145 pmipal Use the protected mode interface for palette changes. 146 147 mtrr:n setup memory type range registers for the vesafb framebuffer 148 where n: 149 0 - disabled (equivalent to nomtrr) (default) 150 1 - uncachable 151 2 - write-back 152 3 - write-combining 153 4 - write-through 154 155 If you see the following in dmesg, choose the type that matches the 156 old one. In this example, use "mtrr:2". 157 ... 158 mtrr: type mismatch for e0000000,8000000 old: write-back new: write-combining 159 ... 160 161 nomtrr disable mtrr 162 163 vremap:n 164 remap 'n' MiB of video RAM. If 0 or not specified, remap memory 165 according to video mode. (2.5.66 patch/idea by Antonino Daplas 166 reversed to give override possibility (allocate more fb memory 167 than the kernel would) to 2.4 by tmb@iki.fi) 168 169 vtotal:n 170 if the video BIOS of your card incorrectly determines the total 171 amount of video RAM, use this option to override the BIOS (in MiB). 172 173 Have fun! 174 175 Gerd 176 177 -- 178 Gerd Knorr <kraxel@goldbach.in-berlin.de> 179 180 Minor (mostly typo) changes 181 by Nico Schmoigl <schmoigl@rumms.uni-mannheim.de>