Documentation/fb/vesafb.rst - linux - Git at Google

 ===============
 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/admin-guide/svga.rst 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>
	===============
	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/admin-guide/svga.rst 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>