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diff --git a/Documentation/fb/vesafb.rst b/Documentation/fb/vesafb.rst new file mode 100644 index 000000000000..2ed0dfb661cf --- /dev/null +++ b/Documentation/fb/vesafb.rst @@ -0,0 +1,192 @@ +=============== +What is vesafb? +=============== + +This is a generic driver for a graphic framebuffer on intel boxes. + +The idea is simple: Turn on graphics mode at boot time with the help +of the BIOS, and use this as framebuffer device /dev/fb0, like the m68k +(and other) ports do. + +This means we decide at boot time whenever we want to run in text or +graphics mode. Switching mode later on (in protected mode) is +impossible; BIOS calls work in real mode only. VESA BIOS Extensions +Version 2.0 are required, because we need a linear frame buffer. + +Advantages: + + * It provides a nice large console (128 cols + 48 lines with 1024x768) + without using tiny, unreadable fonts. + * You can run XF68_FBDev on top of /dev/fb0 (=> non-accelerated X11 + support for every VBE 2.0 compliant graphics board). + * Most important: boot logo :-) + +Disadvantages: + + * graphic mode is slower than text mode... + + +How to use it? +============== + +Switching modes is done using the vga=... boot parameter. Read +Documentation/svga.txt for details. + +You should compile in both vgacon (for text mode) and vesafb (for +graphics mode). Which of them takes over the console depends on +whenever the specified mode is text or graphics. + +The graphic modes are NOT in the list which you get if you boot with +vga=ask and hit return. The mode you wish to use is derived from the +VESA mode number. Here are those VESA mode numbers: + +====== ======= ======= ======== ========= +colors 640x480 800x600 1024x768 1280x1024 +====== ======= ======= ======== ========= +256 0x101 0x103 0x105 0x107 +32k 0x110 0x113 0x116 0x119 +64k 0x111 0x114 0x117 0x11A +16M 0x112 0x115 0x118 0x11B +====== ======= ======= ======== ========= + + +The video mode number of the Linux kernel is the VESA mode number plus +0x200: + + Linux_kernel_mode_number = VESA_mode_number + 0x200 + +So the table for the Kernel mode numbers are: + +====== ======= ======= ======== ========= +colors 640x480 800x600 1024x768 1280x1024 +====== ======= ======= ======== ========= +256 0x301 0x303 0x305 0x307 +32k 0x310 0x313 0x316 0x319 +64k 0x311 0x314 0x317 0x31A +16M 0x312 0x315 0x318 0x31B +====== ======= ======= ======== ========= + +To enable one of those modes you have to specify "vga=ask" in the +lilo.conf file and rerun LILO. Then you can type in the desired +mode at the "vga=ask" prompt. For example if you like to use +1024x768x256 colors you have to say "305" at this prompt. + +If this does not work, this might be because your BIOS does not support +linear framebuffers or because it does not support this mode at all. +Even if your board does, it might be the BIOS which does not. VESA BIOS +Extensions v2.0 are required, 1.2 is NOT sufficient. You will get a +"bad mode number" message if something goes wrong. + +1. Note: LILO cannot handle hex, for booting directly with + "vga=mode-number" you have to transform the numbers to decimal. +2. Note: Some newer versions of LILO appear to work with those hex values, + if you set the 0x in front of the numbers. + +X11 +=== + +XF68_FBDev should work just fine, but it is non-accelerated. Running +another (accelerated) X-Server like XF86_SVGA might or might not work. +It depends on X-Server and graphics board. + +The X-Server must restore the video mode correctly, else you end up +with a broken console (and vesafb cannot do anything about this). + + +Refresh rates +============= + +There is no way to change the vesafb video mode and/or timings after +booting linux. If you are not happy with the 60 Hz refresh rate, you +have these options: + + * configure and load the DOS-Tools for the graphics board (if + available) and boot linux with loadlin. + * use a native driver (matroxfb/atyfb) instead if vesafb. If none + is available, write a new one! + * VBE 3.0 might work too. I have neither a gfx board with VBE 3.0 + support nor the specs, so I have not checked this yet. + + +Configuration +============= + +The VESA BIOS provides protected mode interface for changing +some parameters. vesafb can use it for palette changes and +to pan the display. It is turned off by default because it +seems not to work with some BIOS versions, but there are options +to turn it on. + +You can pass options to vesafb using "video=vesafb:option" on +the kernel command line. Multiple options should be separated +by comma, like this: "video=vesafb:ypan,inverse" + +Accepted options: + +inverse use inverse color map + +========= ====================================================================== +ypan enable display panning using the VESA protected mode + interface. The visible screen is just a window of the + video memory, console scrolling is done by changing the + start of the window. + + pro: + + * scrolling (fullscreen) is fast, because there is + no need to copy around data. + * You'll get scrollback (the Shift-PgUp thing), + the video memory can be used as scrollback buffer + + kontra: + + * scrolling only parts of the screen causes some + ugly flicker effects (boot logo flickers for + example). + +ywrap Same as ypan, but assumes your gfx board can wrap-around + the video memory (i.e. starts reading from top if it + reaches the end of video memory). Faster than ypan. + +redraw Scroll by redrawing the affected part of the screen, this + is the safe (and slow) default. + + +vgapal Use the standard vga registers for palette changes. + This is the default. +pmipal Use the protected mode interface for palette changes. + +mtrr:n Setup memory type range registers for the vesafb framebuffer + where n: + + - 0 - disabled (equivalent to nomtrr) (default) + - 1 - uncachable + - 2 - write-back + - 3 - write-combining + - 4 - write-through + + If you see the following in dmesg, choose the type that matches the + old one. In this example, use "mtrr:2". +... +mtrr: type mismatch for e0000000,8000000 old: write-back new: + write-combining +... + +nomtrr disable mtrr + +vremap:n + Remap 'n' MiB of video RAM. If 0 or not specified, remap memory + according to video mode. (2.5.66 patch/idea by Antonino Daplas + reversed to give override possibility (allocate more fb memory + than the kernel would) to 2.4 by tmb@iki.fi) + +vtotal:n If the video BIOS of your card incorrectly determines the total + amount of video RAM, use this option to override the BIOS (in MiB). +========= ====================================================================== + +Have fun! + +Gerd Knorr <kraxel@goldbach.in-berlin.de> + +Minor (mostly typo) changes +by Nico Schmoigl <schmoigl@rumms.uni-mannheim.de> |