diff options
Diffstat (limited to 'Documentation/fb/fbcon.txt')
| -rw-r--r-- | Documentation/fb/fbcon.txt | 347 |
1 files changed, 0 insertions, 347 deletions
diff --git a/Documentation/fb/fbcon.txt b/Documentation/fb/fbcon.txt deleted file mode 100644 index 60a5ec04e8f0..000000000000 --- a/Documentation/fb/fbcon.txt +++ /dev/null @@ -1,347 +0,0 @@ -The Framebuffer Console -======================= - - The framebuffer console (fbcon), as its name implies, is a text -console running on top of the framebuffer device. It has the functionality of -any standard text console driver, such as the VGA console, with the added -features that can be attributed to the graphical nature of the framebuffer. - - In the x86 architecture, the framebuffer console is optional, and -some even treat it as a toy. For other architectures, it is the only available -display device, text or graphical. - - What are the features of fbcon? The framebuffer console supports -high resolutions, varying font types, display rotation, primitive multihead, -etc. Theoretically, multi-colored fonts, blending, aliasing, and any feature -made available by the underlying graphics card are also possible. - -A. Configuration - - The framebuffer console can be enabled by using your favorite kernel -configuration tool. It is under Device Drivers->Graphics Support->Frame -buffer Devices->Console display driver support->Framebuffer Console Support. -Select 'y' to compile support statically or 'm' for module support. The -module will be fbcon. - - In order for fbcon to activate, at least one framebuffer driver is -required, so choose from any of the numerous drivers available. For x86 -systems, they almost universally have VGA cards, so vga16fb and vesafb will -always be available. However, using a chipset-specific driver will give you -more speed and features, such as the ability to change the video mode -dynamically. - - To display the penguin logo, choose any logo available in Graphics -support->Bootup logo. - - Also, you will need to select at least one compiled-in font, but if -you don't do anything, the kernel configuration tool will select one for you, -usually an 8x16 font. - -GOTCHA: A common bug report is enabling the framebuffer without enabling the -framebuffer console. Depending on the driver, you may get a blanked or -garbled display, but the system still boots to completion. If you are -fortunate to have a driver that does not alter the graphics chip, then you -will still get a VGA console. - -B. Loading - -Possible scenarios: - -1. Driver and fbcon are compiled statically - - Usually, fbcon will automatically take over your console. The notable - exception is vesafb. It needs to be explicitly activated with the - vga= boot option parameter. - -2. Driver is compiled statically, fbcon is compiled as a module - - Depending on the driver, you either get a standard console, or a - garbled display, as mentioned above. To get a framebuffer console, - do a 'modprobe fbcon'. - -3. Driver is compiled as a module, fbcon is compiled statically - - You get your standard console. Once the driver is loaded with - 'modprobe xxxfb', fbcon automatically takes over the console with - the possible exception of using the fbcon=map:n option. See below. - -4. Driver and fbcon are compiled as a module. - - You can load them in any order. Once both are loaded, fbcon will take - over the console. - -C. Boot options - - The framebuffer console has several, largely unknown, boot options - that can change its behavior. - -1. fbcon=font:<name> - - Select the initial font to use. The value 'name' can be any of the - compiled-in fonts: 10x18, 6x10, 7x14, Acorn8x8, MINI4x6, - PEARL8x8, ProFont6x11, SUN12x22, SUN8x16, VGA8x16, VGA8x8. - - Note, not all drivers can handle font with widths not divisible by 8, - such as vga16fb. - -2. fbcon=scrollback:<value>[k] - - The scrollback buffer is memory that is used to preserve display - contents that has already scrolled past your view. This is accessed - by using the Shift-PageUp key combination. The value 'value' is any - integer. It defaults to 32KB. The 'k' suffix is optional, and will - multiply the 'value' by 1024. - -3. fbcon=map:<0123> - - This is an interesting option. It tells which driver gets mapped to - which console. The value '0123' is a sequence that gets repeated until - the total length is 64 which is the number of consoles available. In - the above example, it is expanded to 012301230123... and the mapping - will be: - - tty | 1 2 3 4 5 6 7 8 9 ... - fb | 0 1 2 3 0 1 2 3 0 ... - - ('cat /proc/fb' should tell you what the fb numbers are) - - One side effect that may be useful is using a map value that exceeds - the number of loaded fb drivers. For example, if only one driver is - available, fb0, adding fbcon=map:1 tells fbcon not to take over the - console. - - Later on, when you want to map the console the to the framebuffer - device, you can use the con2fbmap utility. - -4. fbcon=vc:<n1>-<n2> - - This option tells fbcon to take over only a range of consoles as - specified by the values 'n1' and 'n2'. The rest of the consoles - outside the given range will still be controlled by the standard - console driver. - - NOTE: For x86 machines, the standard console is the VGA console which - is typically located on the same video card. Thus, the consoles that - are controlled by the VGA console will be garbled. - -4. fbcon=rotate:<n> - - This option changes the orientation angle of the console display. The - value 'n' accepts the following: - - 0 - normal orientation (0 degree) - 1 - clockwise orientation (90 degrees) - 2 - upside down orientation (180 degrees) - 3 - counterclockwise orientation (270 degrees) - - The angle can be changed anytime afterwards by 'echoing' the same - numbers to any one of the 2 attributes found in - /sys/class/graphics/fbcon: - - rotate - rotate the display of the active console - rotate_all - rotate the display of all consoles - - Console rotation will only become available if Framebuffer Console - Rotation support is compiled in your kernel. - - NOTE: This is purely console rotation. Any other applications that - use the framebuffer will remain at their 'normal' orientation. - Actually, the underlying fb driver is totally ignorant of console - rotation. - -5. fbcon=margin:<color> - - This option specifies the color of the margins. The margins are the - leftover area at the right and the bottom of the screen that are not - used by text. By default, this area will be black. The 'color' value - is an integer number that depends on the framebuffer driver being used. - -6. fbcon=nodefer - - If the kernel is compiled with deferred fbcon takeover support, normally - the framebuffer contents, left in place by the firmware/bootloader, will - be preserved until there actually is some text is output to the console. - This option causes fbcon to bind immediately to the fbdev device. - -7. fbcon=logo-pos:<location> - - The only possible 'location' is 'center' (without quotes), and when - given, the bootup logo is moved from the default top-left corner - location to the center of the framebuffer. If more than one logo is - displayed due to multiple CPUs, the collected line of logos is moved - as a whole. - -C. Attaching, Detaching and Unloading - -Before going on to how to attach, detach and unload the framebuffer console, an -illustration of the dependencies may help. - -The console layer, as with most subsystems, needs a driver that interfaces with -the hardware. Thus, in a VGA console: - -console ---> VGA driver ---> hardware. - -Assuming the VGA driver can be unloaded, one must first unbind the VGA driver -from the console layer before unloading the driver. The VGA driver cannot be -unloaded if it is still bound to the console layer. (See -Documentation/console/console.txt for more information). - -This is more complicated in the case of the framebuffer console (fbcon), -because fbcon is an intermediate layer between the console and the drivers: - -console ---> fbcon ---> fbdev drivers ---> hardware - -The fbdev drivers cannot be unloaded if bound to fbcon, and fbcon cannot -be unloaded if it's bound to the console layer. - -So to unload the fbdev drivers, one must first unbind fbcon from the console, -then unbind the fbdev drivers from fbcon. Fortunately, unbinding fbcon from -the console layer will automatically unbind framebuffer drivers from -fbcon. Thus, there is no need to explicitly unbind the fbdev drivers from -fbcon. - -So, how do we unbind fbcon from the console? Part of the answer is in -Documentation/console/console.txt. To summarize: - -Echo a value to the bind file that represents the framebuffer console -driver. So assuming vtcon1 represents fbcon, then: - -echo 1 > sys/class/vtconsole/vtcon1/bind - attach framebuffer console to - console layer -echo 0 > sys/class/vtconsole/vtcon1/bind - detach framebuffer console from - console layer - -If fbcon is detached from the console layer, your boot console driver (which is -usually VGA text mode) will take over. A few drivers (rivafb and i810fb) will -restore VGA text mode for you. With the rest, before detaching fbcon, you -must take a few additional steps to make sure that your VGA text mode is -restored properly. The following is one of the several methods that you can do: - -1. Download or install vbetool. This utility is included with most - distributions nowadays, and is usually part of the suspend/resume tool. - -2. In your kernel configuration, ensure that CONFIG_FRAMEBUFFER_CONSOLE is set - to 'y' or 'm'. Enable one or more of your favorite framebuffer drivers. - -3. Boot into text mode and as root run: - - vbetool vbestate save > <vga state file> - - The above command saves the register contents of your graphics - hardware to <vga state file>. You need to do this step only once as - the state file can be reused. - -4. If fbcon is compiled as a module, load fbcon by doing: - - modprobe fbcon - -5. Now to detach fbcon: - - vbetool vbestate restore < <vga state file> && \ - echo 0 > /sys/class/vtconsole/vtcon1/bind - -6. That's it, you're back to VGA mode. And if you compiled fbcon as a module, - you can unload it by 'rmmod fbcon'. - -7. To reattach fbcon: - - echo 1 > /sys/class/vtconsole/vtcon1/bind - -8. Once fbcon is unbound, all drivers registered to the system will also -become unbound. This means that fbcon and individual framebuffer drivers -can be unloaded or reloaded at will. Reloading the drivers or fbcon will -automatically bind the console, fbcon and the drivers together. Unloading -all the drivers without unloading fbcon will make it impossible for the -console to bind fbcon. - -Notes for vesafb users: -======================= - -Unfortunately, if your bootline includes a vga=xxx parameter that sets the -hardware in graphics mode, such as when loading vesafb, vgacon will not load. -Instead, vgacon will replace the default boot console with dummycon, and you -won't get any display after detaching fbcon. Your machine is still alive, so -you can reattach vesafb. However, to reattach vesafb, you need to do one of -the following: - -Variation 1: - - a. Before detaching fbcon, do - - vbetool vbemode save > <vesa state file> # do once for each vesafb mode, - # the file can be reused - - b. Detach fbcon as in step 5. - - c. Attach fbcon - - vbetool vbestate restore < <vesa state file> && \ - echo 1 > /sys/class/vtconsole/vtcon1/bind - -Variation 2: - - a. Before detaching fbcon, do: - echo <ID> > /sys/class/tty/console/bind - - - vbetool vbemode get - - b. Take note of the mode number - - b. Detach fbcon as in step 5. - - c. Attach fbcon: - - vbetool vbemode set <mode number> && \ - echo 1 > /sys/class/vtconsole/vtcon1/bind - -Samples: -======== - -Here are 2 sample bash scripts that you can use to bind or unbind the -framebuffer console driver if you are on an X86 box: - ---------------------------------------------------------------------------- -#!/bin/bash -# Unbind fbcon - -# Change this to where your actual vgastate file is located -# Or Use VGASTATE=$1 to indicate the state file at runtime -VGASTATE=/tmp/vgastate - -# path to vbetool -VBETOOL=/usr/local/bin - - -for (( i = 0; i < 16; i++)) -do - if test -x /sys/class/vtconsole/vtcon$i; then - if [ `cat /sys/class/vtconsole/vtcon$i/name | grep -c "frame buffer"` \ - = 1 ]; then - if test -x $VBETOOL/vbetool; then - echo Unbinding vtcon$i - $VBETOOL/vbetool vbestate restore < $VGASTATE - echo 0 > /sys/class/vtconsole/vtcon$i/bind - fi - fi - fi -done - ---------------------------------------------------------------------------- -#!/bin/bash -# Bind fbcon - -for (( i = 0; i < 16; i++)) -do - if test -x /sys/class/vtconsole/vtcon$i; then - if [ `cat /sys/class/vtconsole/vtcon$i/name | grep -c "frame buffer"` \ - = 1 ]; then - echo Unbinding vtcon$i - echo 1 > /sys/class/vtconsole/vtcon$i/bind - fi - fi -done ---------------------------------------------------------------------------- - --- -Antonino Daplas <adaplas@pol.net> |