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diff --git a/Documentation/fb/fbcon.txt b/Documentation/fb/fbcon.txt new file mode 100644 index 0000000..08dce0f --- /dev/null +++ b/Documentation/fb/fbcon.txt @@ -0,0 +1,152 @@ +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->Support for +framebuffer devices->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 Logo +Configuration->Boot up logo. + + Also, you will need to select at least one compiled-in fonts, 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: VGA8x16, 7x14, 10x18, VGA8x8, MINI4x6, RomanLarge, + SUN8x16, SUN12x22, ProFont6x11, Acorn8x8, PEARL8x8. + + 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/fb{x} + + con_rotate - rotate the display of the active console + con_rotate_all - rotate the display of all consoles + + Console rotation will only become available if 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. + +--- +Antonino Daplas <adaplas@pol.net> |
