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Based on kernel version 3.13. Page generated on 2014-01-20 22:02 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>
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