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ab42b818 | 1 | ======================= |
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2 | The Framebuffer Console |
3 | ======================= | |
4 | ||
ab42b818 | 5 | The framebuffer console (fbcon), as its name implies, is a text |
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6 | console running on top of the framebuffer device. It has the functionality of |
7 | any standard text console driver, such as the VGA console, with the added | |
8 | features that can be attributed to the graphical nature of the framebuffer. | |
9 | ||
ab42b818 | 10 | In the x86 architecture, the framebuffer console is optional, and |
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11 | some even treat it as a toy. For other architectures, it is the only available |
12 | display device, text or graphical. | |
13 | ||
ab42b818 | 14 | What are the features of fbcon? The framebuffer console supports |
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15 | high resolutions, varying font types, display rotation, primitive multihead, |
16 | etc. Theoretically, multi-colored fonts, blending, aliasing, and any feature | |
17 | made available by the underlying graphics card are also possible. | |
18 | ||
19 | A. Configuration | |
ab42b818 | 20 | ================ |
efb985f6 | 21 | |
ab42b818 | 22 | The framebuffer console can be enabled by using your favorite kernel |
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23 | configuration tool. It is under Device Drivers->Graphics Support-> |
24 | Console display driver support->Framebuffer Console Support. | |
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25 | Select 'y' to compile support statically or 'm' for module support. The |
26 | module will be fbcon. | |
efb985f6 | 27 | |
ab42b818 | 28 | In order for fbcon to activate, at least one framebuffer driver is |
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29 | required, so choose from any of the numerous drivers available. For x86 |
30 | systems, they almost universally have VGA cards, so vga16fb and vesafb will | |
31 | always be available. However, using a chipset-specific driver will give you | |
32 | more speed and features, such as the ability to change the video mode | |
33 | dynamically. | |
34 | ||
ab42b818 | 35 | To display the penguin logo, choose any logo available in Graphics |
f3968452 | 36 | support->Bootup logo. |
efb985f6 | 37 | |
ab42b818 | 38 | Also, you will need to select at least one compiled-in font, but if |
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39 | you don't do anything, the kernel configuration tool will select one for you, |
40 | usually an 8x16 font. | |
41 | ||
42 | GOTCHA: A common bug report is enabling the framebuffer without enabling the | |
43 | framebuffer console. Depending on the driver, you may get a blanked or | |
44 | garbled display, but the system still boots to completion. If you are | |
45 | fortunate to have a driver that does not alter the graphics chip, then you | |
46 | will still get a VGA console. | |
47 | ||
48 | B. Loading | |
ab42b818 | 49 | ========== |
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50 | |
51 | Possible scenarios: | |
52 | ||
53 | 1. Driver and fbcon are compiled statically | |
54 | ||
55 | Usually, fbcon will automatically take over your console. The notable | |
56 | exception is vesafb. It needs to be explicitly activated with the | |
57 | vga= boot option parameter. | |
58 | ||
59 | 2. Driver is compiled statically, fbcon is compiled as a module | |
60 | ||
61 | Depending on the driver, you either get a standard console, or a | |
62 | garbled display, as mentioned above. To get a framebuffer console, | |
63 | do a 'modprobe fbcon'. | |
64 | ||
65 | 3. Driver is compiled as a module, fbcon is compiled statically | |
66 | ||
67 | You get your standard console. Once the driver is loaded with | |
68 | 'modprobe xxxfb', fbcon automatically takes over the console with | |
69 | the possible exception of using the fbcon=map:n option. See below. | |
70 | ||
71 | 4. Driver and fbcon are compiled as a module. | |
72 | ||
73 | You can load them in any order. Once both are loaded, fbcon will take | |
74 | over the console. | |
75 | ||
76 | C. Boot options | |
77 | ||
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78 | The framebuffer console has several, largely unknown, boot options |
79 | that can change its behavior. | |
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80 | |
81 | 1. fbcon=font:<name> | |
82 | ||
ab42b818 | 83 | Select the initial font to use. The value 'name' can be any of the |
eda4a7bf | 84 | compiled-in fonts: 10x18, 6x10, 6x8, 7x14, Acorn8x8, MINI4x6, |
0ad6be30 | 85 | PEARL8x8, ProFont6x11, SUN12x22, SUN8x16, TER16x32, VGA8x16, VGA8x8. |
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86 | |
87 | Note, not all drivers can handle font with widths not divisible by 8, | |
ab42b818 | 88 | such as vga16fb. |
efb985f6 | 89 | |
efb985f6 | 90 | |
cc3c2a62 | 91 | 2. fbcon=map:<0123> |
efb985f6 | 92 | |
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93 | This is an interesting option. It tells which driver gets mapped to |
94 | which console. The value '0123' is a sequence that gets repeated until | |
95 | the total length is 64 which is the number of consoles available. In | |
96 | the above example, it is expanded to 012301230123... and the mapping | |
97 | will be:: | |
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98 | |
99 | tty | 1 2 3 4 5 6 7 8 9 ... | |
100 | fb | 0 1 2 3 0 1 2 3 0 ... | |
101 | ||
102 | ('cat /proc/fb' should tell you what the fb numbers are) | |
103 | ||
104 | One side effect that may be useful is using a map value that exceeds | |
105 | the number of loaded fb drivers. For example, if only one driver is | |
106 | available, fb0, adding fbcon=map:1 tells fbcon not to take over the | |
107 | console. | |
108 | ||
109 | Later on, when you want to map the console the to the framebuffer | |
110 | device, you can use the con2fbmap utility. | |
111 | ||
cc3c2a62 | 112 | 3. fbcon=vc:<n1>-<n2> |
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113 | |
114 | This option tells fbcon to take over only a range of consoles as | |
115 | specified by the values 'n1' and 'n2'. The rest of the consoles | |
116 | outside the given range will still be controlled by the standard | |
117 | console driver. | |
118 | ||
119 | NOTE: For x86 machines, the standard console is the VGA console which | |
120 | is typically located on the same video card. Thus, the consoles that | |
121 | are controlled by the VGA console will be garbled. | |
122 | ||
cc3c2a62 | 123 | 4. fbcon=rotate:<n> |
efb985f6 | 124 | |
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125 | This option changes the orientation angle of the console display. The |
126 | value 'n' accepts the following: | |
efb985f6 | 127 | |
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128 | - 0 - normal orientation (0 degree) |
129 | - 1 - clockwise orientation (90 degrees) | |
130 | - 2 - upside down orientation (180 degrees) | |
131 | - 3 - counterclockwise orientation (270 degrees) | |
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132 | |
133 | The angle can be changed anytime afterwards by 'echoing' the same | |
134 | numbers to any one of the 2 attributes found in | |
f3968452 | 135 | /sys/class/graphics/fbcon: |
efb985f6 | 136 | |
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137 | - rotate - rotate the display of the active console |
138 | - rotate_all - rotate the display of all consoles | |
efb985f6 | 139 | |
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140 | Console rotation will only become available if Framebuffer Console |
141 | Rotation support is compiled in your kernel. | |
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142 | |
143 | NOTE: This is purely console rotation. Any other applications that | |
f3968452 | 144 | use the framebuffer will remain at their 'normal' orientation. |
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145 | Actually, the underlying fb driver is totally ignorant of console |
146 | rotation. | |
147 | ||
cc3c2a62 | 148 | 5. fbcon=margin:<color> |
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149 | |
150 | This option specifies the color of the margins. The margins are the | |
151 | leftover area at the right and the bottom of the screen that are not | |
152 | used by text. By default, this area will be black. The 'color' value | |
176780c7 | 153 | is an integer number that depends on the framebuffer driver being used. |
74c1c8b3 | 154 | |
cc3c2a62 | 155 | 6. fbcon=nodefer |
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156 | |
157 | If the kernel is compiled with deferred fbcon takeover support, normally | |
158 | the framebuffer contents, left in place by the firmware/bootloader, will | |
159 | be preserved until there actually is some text is output to the console. | |
160 | This option causes fbcon to bind immediately to the fbdev device. | |
161 | ||
cc3c2a62 | 162 | 7. fbcon=logo-pos:<location> |
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163 | |
164 | The only possible 'location' is 'center' (without quotes), and when | |
165 | given, the bootup logo is moved from the default top-left corner | |
166 | location to the center of the framebuffer. If more than one logo is | |
167 | displayed due to multiple CPUs, the collected line of logos is moved | |
168 | as a whole. | |
169 | ||
cc3c2a62 | 170 | 8. fbcon=logo-count:<n> |
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171 | |
172 | The value 'n' overrides the number of bootup logos. 0 disables the | |
173 | logo, and -1 gives the default which is the number of online CPUs. | |
174 | ||
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175 | C. Attaching, Detaching and Unloading |
176 | ||
f3968452 | 177 | Before going on to how to attach, detach and unload the framebuffer console, an |
418d1ce6 | 178 | illustration of the dependencies may help. |
a4a73e1f | 179 | |
418d1ce6 | 180 | The console layer, as with most subsystems, needs a driver that interfaces with |
ab42b818 | 181 | the hardware. Thus, in a VGA console:: |
a4a73e1f | 182 | |
ab42b818 | 183 | console ---> VGA driver ---> hardware. |
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184 | |
185 | Assuming the VGA driver can be unloaded, one must first unbind the VGA driver | |
186 | from the console layer before unloading the driver. The VGA driver cannot be | |
187 | unloaded if it is still bound to the console layer. (See | |
baa293e9 | 188 | Documentation/driver-api/console.rst for more information). |
418d1ce6 | 189 | |
670e9f34 | 190 | This is more complicated in the case of the framebuffer console (fbcon), |
ab42b818 | 191 | because fbcon is an intermediate layer between the console and the drivers:: |
418d1ce6 | 192 | |
ab42b818 | 193 | console ---> fbcon ---> fbdev drivers ---> hardware |
418d1ce6 | 194 | |
f3968452 | 195 | The fbdev drivers cannot be unloaded if bound to fbcon, and fbcon cannot |
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196 | be unloaded if it's bound to the console layer. |
197 | ||
198 | So to unload the fbdev drivers, one must first unbind fbcon from the console, | |
199 | then unbind the fbdev drivers from fbcon. Fortunately, unbinding fbcon from | |
200 | the console layer will automatically unbind framebuffer drivers from | |
201 | fbcon. Thus, there is no need to explicitly unbind the fbdev drivers from | |
202 | fbcon. | |
203 | ||
204 | So, how do we unbind fbcon from the console? Part of the answer is in | |
baa293e9 | 205 | Documentation/driver-api/console.rst. To summarize: |
418d1ce6 | 206 | |
6690075d | 207 | Echo a value to the bind file that represents the framebuffer console |
ab42b818 | 208 | driver. So assuming vtcon1 represents fbcon, then:: |
418d1ce6 | 209 | |
abb9c078 | 210 | echo 1 > /sys/class/vtconsole/vtcon1/bind - attach framebuffer console to |
ab42b818 | 211 | console layer |
abb9c078 | 212 | echo 0 > /sys/class/vtconsole/vtcon1/bind - detach framebuffer console from |
ab42b818 | 213 | console layer |
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214 | |
215 | If fbcon is detached from the console layer, your boot console driver (which is | |
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216 | usually VGA text mode) will take over. A few drivers (rivafb and i810fb) will |
217 | restore VGA text mode for you. With the rest, before detaching fbcon, you | |
218 | must take a few additional steps to make sure that your VGA text mode is | |
219 | restored properly. The following is one of the several methods that you can do: | |
220 | ||
221 | 1. Download or install vbetool. This utility is included with most | |
222 | distributions nowadays, and is usually part of the suspend/resume tool. | |
223 | ||
224 | 2. In your kernel configuration, ensure that CONFIG_FRAMEBUFFER_CONSOLE is set | |
225 | to 'y' or 'm'. Enable one or more of your favorite framebuffer drivers. | |
226 | ||
ab42b818 | 227 | 3. Boot into text mode and as root run:: |
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228 | |
229 | vbetool vbestate save > <vga state file> | |
230 | ||
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231 | The above command saves the register contents of your graphics |
232 | hardware to <vga state file>. You need to do this step only once as | |
233 | the state file can be reused. | |
a4a73e1f | 234 | |
ab42b818 | 235 | 4. If fbcon is compiled as a module, load fbcon by doing:: |
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236 | |
237 | modprobe fbcon | |
238 | ||
ab42b818 | 239 | 5. Now to detach fbcon:: |
a4a73e1f | 240 | |
418d1ce6 | 241 | vbetool vbestate restore < <vga state file> && \ |
6690075d | 242 | echo 0 > /sys/class/vtconsole/vtcon1/bind |
a4a73e1f | 243 | |
418d1ce6 | 244 | 6. That's it, you're back to VGA mode. And if you compiled fbcon as a module, |
f3968452 | 245 | you can unload it by 'rmmod fbcon'. |
a4a73e1f | 246 | |
ab42b818 | 247 | 7. To reattach fbcon:: |
a4a73e1f | 248 | |
6690075d | 249 | echo 1 > /sys/class/vtconsole/vtcon1/bind |
a4a73e1f | 250 | |
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251 | 8. Once fbcon is unbound, all drivers registered to the system will also |
252 | become unbound. This means that fbcon and individual framebuffer drivers | |
253 | can be unloaded or reloaded at will. Reloading the drivers or fbcon will | |
254 | automatically bind the console, fbcon and the drivers together. Unloading | |
255 | all the drivers without unloading fbcon will make it impossible for the | |
256 | console to bind fbcon. | |
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257 | |
258 | Notes for vesafb users: | |
259 | ======================= | |
260 | ||
261 | Unfortunately, if your bootline includes a vga=xxx parameter that sets the | |
262 | hardware in graphics mode, such as when loading vesafb, vgacon will not load. | |
263 | Instead, vgacon will replace the default boot console with dummycon, and you | |
264 | won't get any display after detaching fbcon. Your machine is still alive, so | |
265 | you can reattach vesafb. However, to reattach vesafb, you need to do one of | |
266 | the following: | |
267 | ||
268 | Variation 1: | |
269 | ||
ab42b818 | 270 | a. Before detaching fbcon, do:: |
a4a73e1f | 271 | |
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272 | vbetool vbemode save > <vesa state file> # do once for each vesafb mode, |
273 | # the file can be reused | |
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274 | |
275 | b. Detach fbcon as in step 5. | |
276 | ||
ab42b818 | 277 | c. Attach fbcon:: |
a4a73e1f | 278 | |
ab42b818 | 279 | vbetool vbestate restore < <vesa state file> && \ |
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280 | echo 1 > /sys/class/vtconsole/vtcon1/bind |
281 | ||
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282 | Variation 2: |
283 | ||
ab42b818 | 284 | a. Before detaching fbcon, do:: |
418d1ce6 | 285 | |
ab42b818 | 286 | echo <ID> > /sys/class/tty/console/bind |
a4a73e1f | 287 | |
ab42b818 | 288 | vbetool vbemode get |
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289 | |
290 | b. Take note of the mode number | |
291 | ||
292 | b. Detach fbcon as in step 5. | |
293 | ||
ab42b818 | 294 | c. Attach fbcon:: |
a4a73e1f | 295 | |
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296 | vbetool vbemode set <mode number> && \ |
297 | echo 1 > /sys/class/vtconsole/vtcon1/bind | |
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298 | |
299 | Samples: | |
300 | ======== | |
301 | ||
302 | Here are 2 sample bash scripts that you can use to bind or unbind the | |
ab42b818 | 303 | framebuffer console driver if you are on an X86 box:: |
6690075d | 304 | |
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305 | #!/bin/bash |
306 | # Unbind fbcon | |
6690075d | 307 | |
ab42b818 MCC |
308 | # Change this to where your actual vgastate file is located |
309 | # Or Use VGASTATE=$1 to indicate the state file at runtime | |
310 | VGASTATE=/tmp/vgastate | |
6690075d | 311 | |
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312 | # path to vbetool |
313 | VBETOOL=/usr/local/bin | |
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314 | |
315 | ||
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316 | for (( i = 0; i < 16; i++)) |
317 | do | |
318 | if test -x /sys/class/vtconsole/vtcon$i; then | |
319 | if [ `cat /sys/class/vtconsole/vtcon$i/name | grep -c "frame buffer"` \ | |
320 | = 1 ]; then | |
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321 | if test -x $VBETOOL/vbetool; then |
322 | echo Unbinding vtcon$i | |
323 | $VBETOOL/vbetool vbestate restore < $VGASTATE | |
324 | echo 0 > /sys/class/vtconsole/vtcon$i/bind | |
325 | fi | |
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326 | fi |
327 | fi | |
328 | done | |
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329 | |
330 | --------------------------------------------------------------------------- | |
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331 | |
332 | :: | |
333 | ||
334 | #!/bin/bash | |
335 | # Bind fbcon | |
336 | ||
337 | for (( i = 0; i < 16; i++)) | |
338 | do | |
339 | if test -x /sys/class/vtconsole/vtcon$i; then | |
340 | if [ `cat /sys/class/vtconsole/vtcon$i/name | grep -c "frame buffer"` \ | |
341 | = 1 ]; then | |
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342 | echo Unbinding vtcon$i |
343 | echo 1 > /sys/class/vtconsole/vtcon$i/bind | |
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344 | fi |
345 | fi | |
346 | done | |
a4a73e1f | 347 | |
efb985f6 | 348 | Antonino Daplas <adaplas@pol.net> |