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1 | The Framebuffer Console |
2 | ======================= | |
3 | ||
4 | The framebuffer console (fbcon), as its name implies, is a text | |
5 | console running on top of the framebuffer device. It has the functionality of | |
6 | any standard text console driver, such as the VGA console, with the added | |
7 | features that can be attributed to the graphical nature of the framebuffer. | |
8 | ||
9 | In the x86 architecture, the framebuffer console is optional, and | |
10 | some even treat it as a toy. For other architectures, it is the only available | |
11 | display device, text or graphical. | |
12 | ||
13 | What are the features of fbcon? The framebuffer console supports | |
14 | high resolutions, varying font types, display rotation, primitive multihead, | |
15 | etc. Theoretically, multi-colored fonts, blending, aliasing, and any feature | |
16 | made available by the underlying graphics card are also possible. | |
17 | ||
18 | A. Configuration | |
19 | ||
20 | The framebuffer console can be enabled by using your favorite kernel | |
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21 | configuration tool. It is under Device Drivers->Graphics Support->Frame |
22 | buffer Devices->Console display driver support->Framebuffer Console Support. | |
23 | Select 'y' to compile support statically or 'm' for module support. The | |
24 | module will be fbcon. | |
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25 | |
26 | In order for fbcon to activate, at least one framebuffer driver is | |
27 | required, so choose from any of the numerous drivers available. For x86 | |
28 | systems, they almost universally have VGA cards, so vga16fb and vesafb will | |
29 | always be available. However, using a chipset-specific driver will give you | |
30 | more speed and features, such as the ability to change the video mode | |
31 | dynamically. | |
32 | ||
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33 | To display the penguin logo, choose any logo available in Graphics |
34 | support->Bootup logo. | |
efb985f6 | 35 | |
f3968452 | 36 | Also, you will need to select at least one compiled-in font, but if |
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37 | you don't do anything, the kernel configuration tool will select one for you, |
38 | usually an 8x16 font. | |
39 | ||
40 | GOTCHA: A common bug report is enabling the framebuffer without enabling the | |
41 | framebuffer console. Depending on the driver, you may get a blanked or | |
42 | garbled display, but the system still boots to completion. If you are | |
43 | fortunate to have a driver that does not alter the graphics chip, then you | |
44 | will still get a VGA console. | |
45 | ||
46 | B. Loading | |
47 | ||
48 | Possible scenarios: | |
49 | ||
50 | 1. Driver and fbcon are compiled statically | |
51 | ||
52 | Usually, fbcon will automatically take over your console. The notable | |
53 | exception is vesafb. It needs to be explicitly activated with the | |
54 | vga= boot option parameter. | |
55 | ||
56 | 2. Driver is compiled statically, fbcon is compiled as a module | |
57 | ||
58 | Depending on the driver, you either get a standard console, or a | |
59 | garbled display, as mentioned above. To get a framebuffer console, | |
60 | do a 'modprobe fbcon'. | |
61 | ||
62 | 3. Driver is compiled as a module, fbcon is compiled statically | |
63 | ||
64 | You get your standard console. Once the driver is loaded with | |
65 | 'modprobe xxxfb', fbcon automatically takes over the console with | |
66 | the possible exception of using the fbcon=map:n option. See below. | |
67 | ||
68 | 4. Driver and fbcon are compiled as a module. | |
69 | ||
70 | You can load them in any order. Once both are loaded, fbcon will take | |
71 | over the console. | |
72 | ||
73 | C. Boot options | |
74 | ||
75 | The framebuffer console has several, largely unknown, boot options | |
76 | that can change its behavior. | |
77 | ||
78 | 1. fbcon=font:<name> | |
79 | ||
80 | Select the initial font to use. The value 'name' can be any of the | |
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81 | compiled-in fonts: 10x18, 6x10, 7x14, Acorn8x8, MINI4x6, |
82 | PEARL8x8, ProFont6x11, SUN12x22, SUN8x16, VGA8x16, VGA8x8. | |
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83 | |
84 | Note, not all drivers can handle font with widths not divisible by 8, | |
85 | such as vga16fb. | |
86 | ||
87 | 2. fbcon=scrollback:<value>[k] | |
88 | ||
89 | The scrollback buffer is memory that is used to preserve display | |
90 | contents that has already scrolled past your view. This is accessed | |
91 | by using the Shift-PageUp key combination. The value 'value' is any | |
92 | integer. It defaults to 32KB. The 'k' suffix is optional, and will | |
93 | multiply the 'value' by 1024. | |
94 | ||
95 | 3. fbcon=map:<0123> | |
96 | ||
97 | This is an interesting option. It tells which driver gets mapped to | |
98 | which console. The value '0123' is a sequence that gets repeated until | |
99 | the total length is 64 which is the number of consoles available. In | |
100 | the above example, it is expanded to 012301230123... and the mapping | |
101 | will be: | |
102 | ||
103 | tty | 1 2 3 4 5 6 7 8 9 ... | |
104 | fb | 0 1 2 3 0 1 2 3 0 ... | |
105 | ||
106 | ('cat /proc/fb' should tell you what the fb numbers are) | |
107 | ||
108 | One side effect that may be useful is using a map value that exceeds | |
109 | the number of loaded fb drivers. For example, if only one driver is | |
110 | available, fb0, adding fbcon=map:1 tells fbcon not to take over the | |
111 | console. | |
112 | ||
113 | Later on, when you want to map the console the to the framebuffer | |
114 | device, you can use the con2fbmap utility. | |
115 | ||
116 | 4. fbcon=vc:<n1>-<n2> | |
117 | ||
118 | This option tells fbcon to take over only a range of consoles as | |
119 | specified by the values 'n1' and 'n2'. The rest of the consoles | |
120 | outside the given range will still be controlled by the standard | |
121 | console driver. | |
122 | ||
123 | NOTE: For x86 machines, the standard console is the VGA console which | |
124 | is typically located on the same video card. Thus, the consoles that | |
125 | are controlled by the VGA console will be garbled. | |
126 | ||
127 | 4. fbcon=rotate:<n> | |
128 | ||
129 | This option changes the orientation angle of the console display. The | |
130 | value 'n' accepts the following: | |
131 | ||
132 | 0 - normal orientation (0 degree) | |
133 | 1 - clockwise orientation (90 degrees) | |
134 | 2 - upside down orientation (180 degrees) | |
135 | 3 - counterclockwise orientation (270 degrees) | |
136 | ||
137 | The angle can be changed anytime afterwards by 'echoing' the same | |
138 | numbers to any one of the 2 attributes found in | |
f3968452 | 139 | /sys/class/graphics/fbcon: |
efb985f6 | 140 | |
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141 | rotate - rotate the display of the active console |
142 | rotate_all - rotate the display of all consoles | |
efb985f6 | 143 | |
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144 | Console rotation will only become available if Framebuffer Console |
145 | Rotation support is compiled in your kernel. | |
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146 | |
147 | NOTE: This is purely console rotation. Any other applications that | |
f3968452 | 148 | use the framebuffer will remain at their 'normal' orientation. |
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149 | Actually, the underlying fb driver is totally ignorant of console |
150 | rotation. | |
151 | ||
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152 | 5. fbcon=margin:<color> |
153 | ||
154 | This option specifies the color of the margins. The margins are the | |
155 | leftover area at the right and the bottom of the screen that are not | |
156 | used by text. By default, this area will be black. The 'color' value | |
176780c7 | 157 | is an integer number that depends on the framebuffer driver being used. |
74c1c8b3 | 158 | |
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159 | 6. fbcon=nodefer |
160 | ||
161 | If the kernel is compiled with deferred fbcon takeover support, normally | |
162 | the framebuffer contents, left in place by the firmware/bootloader, will | |
163 | be preserved until there actually is some text is output to the console. | |
164 | This option causes fbcon to bind immediately to the fbdev device. | |
165 | ||
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166 | C. Attaching, Detaching and Unloading |
167 | ||
f3968452 | 168 | Before going on to how to attach, detach and unload the framebuffer console, an |
418d1ce6 | 169 | illustration of the dependencies may help. |
a4a73e1f | 170 | |
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171 | The console layer, as with most subsystems, needs a driver that interfaces with |
172 | the hardware. Thus, in a VGA console: | |
a4a73e1f | 173 | |
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174 | console ---> VGA driver ---> hardware. |
175 | ||
176 | Assuming the VGA driver can be unloaded, one must first unbind the VGA driver | |
177 | from the console layer before unloading the driver. The VGA driver cannot be | |
178 | unloaded if it is still bound to the console layer. (See | |
179 | Documentation/console/console.txt for more information). | |
180 | ||
670e9f34 | 181 | This is more complicated in the case of the framebuffer console (fbcon), |
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182 | because fbcon is an intermediate layer between the console and the drivers: |
183 | ||
184 | console ---> fbcon ---> fbdev drivers ---> hardware | |
185 | ||
f3968452 | 186 | The fbdev drivers cannot be unloaded if bound to fbcon, and fbcon cannot |
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187 | be unloaded if it's bound to the console layer. |
188 | ||
189 | So to unload the fbdev drivers, one must first unbind fbcon from the console, | |
190 | then unbind the fbdev drivers from fbcon. Fortunately, unbinding fbcon from | |
191 | the console layer will automatically unbind framebuffer drivers from | |
192 | fbcon. Thus, there is no need to explicitly unbind the fbdev drivers from | |
193 | fbcon. | |
194 | ||
195 | So, how do we unbind fbcon from the console? Part of the answer is in | |
196 | Documentation/console/console.txt. To summarize: | |
197 | ||
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198 | Echo a value to the bind file that represents the framebuffer console |
199 | driver. So assuming vtcon1 represents fbcon, then: | |
418d1ce6 | 200 | |
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201 | echo 1 > sys/class/vtconsole/vtcon1/bind - attach framebuffer console to |
202 | console layer | |
203 | echo 0 > sys/class/vtconsole/vtcon1/bind - detach framebuffer console from | |
204 | console layer | |
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205 | |
206 | If fbcon is detached from the console layer, your boot console driver (which is | |
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207 | usually VGA text mode) will take over. A few drivers (rivafb and i810fb) will |
208 | restore VGA text mode for you. With the rest, before detaching fbcon, you | |
209 | must take a few additional steps to make sure that your VGA text mode is | |
210 | restored properly. The following is one of the several methods that you can do: | |
211 | ||
212 | 1. Download or install vbetool. This utility is included with most | |
213 | distributions nowadays, and is usually part of the suspend/resume tool. | |
214 | ||
215 | 2. In your kernel configuration, ensure that CONFIG_FRAMEBUFFER_CONSOLE is set | |
216 | to 'y' or 'm'. Enable one or more of your favorite framebuffer drivers. | |
217 | ||
218 | 3. Boot into text mode and as root run: | |
219 | ||
220 | vbetool vbestate save > <vga state file> | |
221 | ||
222 | The above command saves the register contents of your graphics | |
223 | hardware to <vga state file>. You need to do this step only once as | |
224 | the state file can be reused. | |
225 | ||
226 | 4. If fbcon is compiled as a module, load fbcon by doing: | |
227 | ||
228 | modprobe fbcon | |
229 | ||
230 | 5. Now to detach fbcon: | |
231 | ||
418d1ce6 | 232 | vbetool vbestate restore < <vga state file> && \ |
6690075d | 233 | echo 0 > /sys/class/vtconsole/vtcon1/bind |
a4a73e1f | 234 | |
418d1ce6 | 235 | 6. That's it, you're back to VGA mode. And if you compiled fbcon as a module, |
f3968452 | 236 | you can unload it by 'rmmod fbcon'. |
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237 | |
238 | 7. To reattach fbcon: | |
239 | ||
6690075d | 240 | echo 1 > /sys/class/vtconsole/vtcon1/bind |
a4a73e1f | 241 | |
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242 | 8. Once fbcon is unbound, all drivers registered to the system will also |
243 | become unbound. This means that fbcon and individual framebuffer drivers | |
244 | can be unloaded or reloaded at will. Reloading the drivers or fbcon will | |
245 | automatically bind the console, fbcon and the drivers together. Unloading | |
246 | all the drivers without unloading fbcon will make it impossible for the | |
247 | console to bind fbcon. | |
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248 | |
249 | Notes for vesafb users: | |
250 | ======================= | |
251 | ||
252 | Unfortunately, if your bootline includes a vga=xxx parameter that sets the | |
253 | hardware in graphics mode, such as when loading vesafb, vgacon will not load. | |
254 | Instead, vgacon will replace the default boot console with dummycon, and you | |
255 | won't get any display after detaching fbcon. Your machine is still alive, so | |
256 | you can reattach vesafb. However, to reattach vesafb, you need to do one of | |
257 | the following: | |
258 | ||
259 | Variation 1: | |
260 | ||
261 | a. Before detaching fbcon, do | |
262 | ||
263 | vbetool vbemode save > <vesa state file> # do once for each vesafb mode, | |
264 | # the file can be reused | |
265 | ||
266 | b. Detach fbcon as in step 5. | |
267 | ||
268 | c. Attach fbcon | |
269 | ||
270 | vbetool vbestate restore < <vesa state file> && \ | |
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271 | echo 1 > /sys/class/vtconsole/vtcon1/bind |
272 | ||
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273 | Variation 2: |
274 | ||
275 | a. Before detaching fbcon, do: | |
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276 | echo <ID> > /sys/class/tty/console/bind |
277 | ||
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278 | |
279 | vbetool vbemode get | |
280 | ||
281 | b. Take note of the mode number | |
282 | ||
283 | b. Detach fbcon as in step 5. | |
284 | ||
285 | c. Attach fbcon: | |
286 | ||
287 | vbetool vbemode set <mode number> && \ | |
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288 | echo 1 > /sys/class/vtconsole/vtcon1/bind |
289 | ||
290 | Samples: | |
291 | ======== | |
292 | ||
293 | Here are 2 sample bash scripts that you can use to bind or unbind the | |
f3968452 | 294 | framebuffer console driver if you are on an X86 box: |
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295 | |
296 | --------------------------------------------------------------------------- | |
297 | #!/bin/bash | |
298 | # Unbind fbcon | |
299 | ||
300 | # Change this to where your actual vgastate file is located | |
301 | # Or Use VGASTATE=$1 to indicate the state file at runtime | |
302 | VGASTATE=/tmp/vgastate | |
303 | ||
304 | # path to vbetool | |
305 | VBETOOL=/usr/local/bin | |
306 | ||
307 | ||
308 | for (( i = 0; i < 16; i++)) | |
309 | do | |
310 | if test -x /sys/class/vtconsole/vtcon$i; then | |
311 | if [ `cat /sys/class/vtconsole/vtcon$i/name | grep -c "frame buffer"` \ | |
312 | = 1 ]; then | |
313 | if test -x $VBETOOL/vbetool; then | |
314 | echo Unbinding vtcon$i | |
315 | $VBETOOL/vbetool vbestate restore < $VGASTATE | |
316 | echo 0 > /sys/class/vtconsole/vtcon$i/bind | |
317 | fi | |
318 | fi | |
319 | fi | |
320 | done | |
321 | ||
322 | --------------------------------------------------------------------------- | |
323 | #!/bin/bash | |
324 | # Bind fbcon | |
325 | ||
326 | for (( i = 0; i < 16; i++)) | |
327 | do | |
328 | if test -x /sys/class/vtconsole/vtcon$i; then | |
329 | if [ `cat /sys/class/vtconsole/vtcon$i/name | grep -c "frame buffer"` \ | |
330 | = 1 ]; then | |
331 | echo Unbinding vtcon$i | |
332 | echo 1 > /sys/class/vtconsole/vtcon$i/bind | |
333 | fi | |
334 | fi | |
335 | done | |
336 | --------------------------------------------------------------------------- | |
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337 | |
338 | -- | |
efb985f6 | 339 | Antonino Daplas <adaplas@pol.net> |