[GitHub/mt8127/android_kernel_alcatel_ttab.git] / Documentation / fb / vesafb.txt


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:

    | 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:

    | 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,invers"

Accepted options:

invers	no comment...

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

--
Gerd Knorr <kraxel@goldbach.in-berlin.de>

Minor (mostly typo) changes 
by Nico Schmoigl <schmoigl@rumms.uni-mannheim.de>
Commit	Line	Data
1da177e4 LT	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
2d9d2fdf	98	* configure and load the DOS-Tools for the graphics board (if
1da177e4 LT	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
d7a465b4 AD	147	mtrr:n setup memory type range registers for the vesafb framebuffer
d7a465b4 AD	148	where n:
8a0934f2	149	0 - disabled (equivalent to nomtrr) (default)
d7a465b4 AD	150	1 - uncachable
d7a465b4 AD	151	2 - write-back
8a0934f2	152	3 - write-combining
d7a465b4 AD	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
1da177e4 LT	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>