1The Framebuffer Console 2======================= 3 4 The framebuffer console (fbcon), as its name implies, is a text 5console running on top of the framebuffer device. It has the functionality of 6any standard text console driver, such as the VGA console, with the added 7features that can be attributed to the graphical nature of the framebuffer. 8 9 In the x86 architecture, the framebuffer console is optional, and 10some even treat it as a toy. For other architectures, it is the only available 11display device, text or graphical. 12 13 What are the features of fbcon? The framebuffer console supports 14high resolutions, varying font types, display rotation, primitive multihead, 15etc. Theoretically, multi-colored fonts, blending, aliasing, and any feature 16made available by the underlying graphics card are also possible. 17 18A. Configuration 19 20 The framebuffer console can be enabled by using your favorite kernel 21configuration tool. It is under Device Drivers->Graphics Support->Support for 22framebuffer devices->Framebuffer Console Support. Select 'y' to compile 23support statically, or 'm' for module support. The module will be fbcon. 24 25 In order for fbcon to activate, at least one framebuffer driver is 26required, so choose from any of the numerous drivers available. For x86 27systems, they almost universally have VGA cards, so vga16fb and vesafb will 28always be available. However, using a chipset-specific driver will give you 29more speed and features, such as the ability to change the video mode 30dynamically. 31 32 To display the penguin logo, choose any logo available in Logo 33Configuration->Boot up logo. 34 35 Also, you will need to select at least one compiled-in fonts, but if 36you don't do anything, the kernel configuration tool will select one for you, 37usually an 8x16 font. 38 39GOTCHA: A common bug report is enabling the framebuffer without enabling the 40framebuffer console. Depending on the driver, you may get a blanked or 41garbled display, but the system still boots to completion. If you are 42fortunate to have a driver that does not alter the graphics chip, then you 43will still get a VGA console. 44 45B. Loading 46 47Possible scenarios: 48 491. Driver and fbcon are compiled statically 50 51 Usually, fbcon will automatically take over your console. The notable 52 exception is vesafb. It needs to be explicitly activated with the 53 vga= boot option parameter. 54 552. Driver is compiled statically, fbcon is compiled as a module 56 57 Depending on the driver, you either get a standard console, or a 58 garbled display, as mentioned above. To get a framebuffer console, 59 do a 'modprobe fbcon'. 60 613. Driver is compiled as a module, fbcon is compiled statically 62 63 You get your standard console. Once the driver is loaded with 64 'modprobe xxxfb', fbcon automatically takes over the console with 65 the possible exception of using the fbcon=map:n option. See below. 66 674. Driver and fbcon are compiled as a module. 68 69 You can load them in any order. Once both are loaded, fbcon will take 70 over the console. 71 72C. Boot options 73 74 The framebuffer console has several, largely unknown, boot options 75 that can change its behavior. 76 771. fbcon=font:<name> 78 79 Select the initial font to use. The value 'name' can be any of the 80 compiled-in fonts: VGA8x16, 7x14, 10x18, VGA8x8, MINI4x6, RomanLarge, 81 SUN8x16, SUN12x22, ProFont6x11, Acorn8x8, PEARL8x8. 82 83 Note, not all drivers can handle font with widths not divisible by 8, 84 such as vga16fb. 85 862. fbcon=scrollback:<value>[k] 87 88 The scrollback buffer is memory that is used to preserve display 89 contents that has already scrolled past your view. This is accessed 90 by using the Shift-PageUp key combination. The value 'value' is any 91 integer. It defaults to 32KB. The 'k' suffix is optional, and will 92 multiply the 'value' by 1024. 93 943. fbcon=map:<0123> 95 96 This is an interesting option. It tells which driver gets mapped to 97 which console. The value '0123' is a sequence that gets repeated until 98 the total length is 64 which is the number of consoles available. In 99 the above example, it is expanded to 012301230123... and the mapping 100 will be: 101 102 tty | 1 2 3 4 5 6 7 8 9 ... 103 fb | 0 1 2 3 0 1 2 3 0 ... 104 105 ('cat /proc/fb' should tell you what the fb numbers are) 106 107 One side effect that may be useful is using a map value that exceeds 108 the number of loaded fb drivers. For example, if only one driver is 109 available, fb0, adding fbcon=map:1 tells fbcon not to take over the 110 console. 111 112 Later on, when you want to map the console the to the framebuffer 113 device, you can use the con2fbmap utility. 114 1154. fbcon=vc:<n1>-<n2> 116 117 This option tells fbcon to take over only a range of consoles as 118 specified by the values 'n1' and 'n2'. The rest of the consoles 119 outside the given range will still be controlled by the standard 120 console driver. 121 122 NOTE: For x86 machines, the standard console is the VGA console which 123 is typically located on the same video card. Thus, the consoles that 124 are controlled by the VGA console will be garbled. 125 1264. fbcon=rotate:<n> 127 128 This option changes the orientation angle of the console display. The 129 value 'n' accepts the following: 130 131 0 - normal orientation (0 degree) 132 1 - clockwise orientation (90 degrees) 133 2 - upside down orientation (180 degrees) 134 3 - counterclockwise orientation (270 degrees) 135 136 The angle can be changed anytime afterwards by 'echoing' the same 137 numbers to any one of the 2 attributes found in 138 /sys/class/graphics/fbcon 139 140 rotate - rotate the display of the active console 141 rotate_all - rotate the display of all consoles 142 143 Console rotation will only become available if Console Rotation 144 Support is compiled in your kernel. 145 146 NOTE: This is purely console rotation. Any other applications that 147 use the framebuffer will remain at their 'normal'orientation. 148 Actually, the underlying fb driver is totally ignorant of console 149 rotation. 150 151C. Attaching, Detaching and Unloading 152 153Before going on how to attach, detach and unload the framebuffer console, an 154illustration of the dependencies may help. 155 156The console layer, as with most subsystems, needs a driver that interfaces with 157the hardware. Thus, in a VGA console: 158 159console ---> VGA driver ---> hardware. 160 161Assuming the VGA driver can be unloaded, one must first unbind the VGA driver 162from the console layer before unloading the driver. The VGA driver cannot be 163unloaded if it is still bound to the console layer. (See 164Documentation/console/console.txt for more information). 165 166This is more complicated in the case of the framebuffer console (fbcon), 167because fbcon is an intermediate layer between the console and the drivers: 168 169console ---> fbcon ---> fbdev drivers ---> hardware 170 171The fbdev drivers cannot be unloaded if it's bound to fbcon, and fbcon cannot 172be unloaded if it's bound to the console layer. 173 174So to unload the fbdev drivers, one must first unbind fbcon from the console, 175then unbind the fbdev drivers from fbcon. Fortunately, unbinding fbcon from 176the console layer will automatically unbind framebuffer drivers from 177fbcon. Thus, there is no need to explicitly unbind the fbdev drivers from 178fbcon. 179 180So, how do we unbind fbcon from the console? Part of the answer is in 181Documentation/console/console.txt. To summarize: 182 183Echo a value to the bind file that represents the framebuffer console 184driver. So assuming vtcon1 represents fbcon, then: 185 186echo 1 > sys/class/vtconsole/vtcon1/bind - attach framebuffer console to 187 console layer 188echo 0 > sys/class/vtconsole/vtcon1/bind - detach framebuffer console from 189 console layer 190 191If fbcon is detached from the console layer, your boot console driver (which is 192usually VGA text mode) will take over. A few drivers (rivafb and i810fb) will 193restore VGA text mode for you. With the rest, before detaching fbcon, you 194must take a few additional steps to make sure that your VGA text mode is 195restored properly. The following is one of the several methods that you can do: 196 1971. Download or install vbetool. This utility is included with most 198 distributions nowadays, and is usually part of the suspend/resume tool. 199 2002. In your kernel configuration, ensure that CONFIG_FRAMEBUFFER_CONSOLE is set 201 to 'y' or 'm'. Enable one or more of your favorite framebuffer drivers. 202 2033. Boot into text mode and as root run: 204 205 vbetool vbestate save > <vga state file> 206 207 The above command saves the register contents of your graphics 208 hardware to <vga state file>. You need to do this step only once as 209 the state file can be reused. 210 2114. If fbcon is compiled as a module, load fbcon by doing: 212 213 modprobe fbcon 214 2155. Now to detach fbcon: 216 217 vbetool vbestate restore < <vga state file> && \ 218 echo 0 > /sys/class/vtconsole/vtcon1/bind 219 2206. That's it, you're back to VGA mode. And if you compiled fbcon as a module, 221 you can unload it by 'rmmod fbcon' 222 2237. To reattach fbcon: 224 225 echo 1 > /sys/class/vtconsole/vtcon1/bind 226 2278. Once fbcon is unbound, all drivers registered to the system will also 228become unbound. This means that fbcon and individual framebuffer drivers 229can be unloaded or reloaded at will. Reloading the drivers or fbcon will 230automatically bind the console, fbcon and the drivers together. Unloading 231all the drivers without unloading fbcon will make it impossible for the 232console to bind fbcon. 233 234Notes for vesafb users: 235======================= 236 237Unfortunately, if your bootline includes a vga=xxx parameter that sets the 238hardware in graphics mode, such as when loading vesafb, vgacon will not load. 239Instead, vgacon will replace the default boot console with dummycon, and you 240won't get any display after detaching fbcon. Your machine is still alive, so 241you can reattach vesafb. However, to reattach vesafb, you need to do one of 242the following: 243 244Variation 1: 245 246 a. Before detaching fbcon, do 247 248 vbetool vbemode save > <vesa state file> # do once for each vesafb mode, 249 # the file can be reused 250 251 b. Detach fbcon as in step 5. 252 253 c. Attach fbcon 254 255 vbetool vbestate restore < <vesa state file> && \ 256 echo 1 > /sys/class/vtconsole/vtcon1/bind 257 258Variation 2: 259 260 a. Before detaching fbcon, do: 261 echo <ID> > /sys/class/tty/console/bind 262 263 264 vbetool vbemode get 265 266 b. Take note of the mode number 267 268 b. Detach fbcon as in step 5. 269 270 c. Attach fbcon: 271 272 vbetool vbemode set <mode number> && \ 273 echo 1 > /sys/class/vtconsole/vtcon1/bind 274 275Samples: 276======== 277 278Here are 2 sample bash scripts that you can use to bind or unbind the 279framebuffer console driver if you are in an X86 box: 280 281--------------------------------------------------------------------------- 282#!/bin/bash 283# Unbind fbcon 284 285# Change this to where your actual vgastate file is located 286# Or Use VGASTATE=$1 to indicate the state file at runtime 287VGASTATE=/tmp/vgastate 288 289# path to vbetool 290VBETOOL=/usr/local/bin 291 292 293for (( i = 0; i < 16; i++)) 294do 295 if test -x /sys/class/vtconsole/vtcon$i; then 296 if [ `cat /sys/class/vtconsole/vtcon$i/name | grep -c "frame buffer"` \ 297 = 1 ]; then 298 if test -x $VBETOOL/vbetool; then 299 echo Unbinding vtcon$i 300 $VBETOOL/vbetool vbestate restore < $VGASTATE 301 echo 0 > /sys/class/vtconsole/vtcon$i/bind 302 fi 303 fi 304 fi 305done 306 307--------------------------------------------------------------------------- 308#!/bin/bash 309# Bind fbcon 310 311for (( i = 0; i < 16; i++)) 312do 313 if test -x /sys/class/vtconsole/vtcon$i; then 314 if [ `cat /sys/class/vtconsole/vtcon$i/name | grep -c "frame buffer"` \ 315 = 1 ]; then 316 echo Unbinding vtcon$i 317 echo 1 > /sys/class/vtconsole/vtcon$i/bind 318 fi 319 fi 320done 321--------------------------------------------------------------------------- 322 323-- 324Antonino Daplas <adaplas@pol.net> 325