1 ======================= 1 =======================
2 The Framebuffer Console 2 The Framebuffer Console
3 ======================= 3 =======================
4 4
5 The framebuffer console (fbcon), as its name i 5 The framebuffer console (fbcon), as its name implies, is a text
6 console running on top of the framebuffer devi 6 console running on top of the framebuffer device. It has the functionality of
7 any standard text console driver, such as the 7 any standard text console driver, such as the VGA console, with the added
8 features that can be attributed to the graphic 8 features that can be attributed to the graphical nature of the framebuffer.
9 9
10 In the x86 architecture, the framebuffer conso 10 In the x86 architecture, the framebuffer console is optional, and
11 some even treat it as a toy. For other archite 11 some even treat it as a toy. For other architectures, it is the only available
12 display device, text or graphical. 12 display device, text or graphical.
13 13
14 What are the features of fbcon? The framebuff 14 What are the features of fbcon? The framebuffer console supports
15 high resolutions, varying font types, display 15 high resolutions, varying font types, display rotation, primitive multihead,
16 etc. Theoretically, multi-colored fonts, blend 16 etc. Theoretically, multi-colored fonts, blending, aliasing, and any feature
17 made available by the underlying graphics card 17 made available by the underlying graphics card are also possible.
18 18
19 A. Configuration 19 A. Configuration
20 ================ 20 ================
21 21
22 The framebuffer console can be enabled by usin 22 The framebuffer console can be enabled by using your favorite kernel
23 configuration tool. It is under Device Driver !! 23 configuration tool. It is under Device Drivers->Graphics Support->Frame
24 Console display driver support->Framebuffer Co !! 24 buffer Devices->Console display driver support->Framebuffer Console Support.
25 Select 'y' to compile support statically or 'm 25 Select 'y' to compile support statically or 'm' for module support. The
26 module will be fbcon. 26 module will be fbcon.
27 27
28 In order for fbcon to activate, at least one f 28 In order for fbcon to activate, at least one framebuffer driver is
29 required, so choose from any of the numerous d 29 required, so choose from any of the numerous drivers available. For x86
30 systems, they almost universally have VGA card 30 systems, they almost universally have VGA cards, so vga16fb and vesafb will
31 always be available. However, using a chipset- 31 always be available. However, using a chipset-specific driver will give you
32 more speed and features, such as the ability t 32 more speed and features, such as the ability to change the video mode
33 dynamically. 33 dynamically.
34 34
35 To display the penguin logo, choose any logo a 35 To display the penguin logo, choose any logo available in Graphics
36 support->Bootup logo. 36 support->Bootup logo.
37 37
38 Also, you will need to select at least one com 38 Also, you will need to select at least one compiled-in font, but if
39 you don't do anything, the kernel configuratio 39 you don't do anything, the kernel configuration tool will select one for you,
40 usually an 8x16 font. 40 usually an 8x16 font.
41 41
42 GOTCHA: A common bug report is enabling the fr 42 GOTCHA: A common bug report is enabling the framebuffer without enabling the
43 framebuffer console. Depending on the driver, 43 framebuffer console. Depending on the driver, you may get a blanked or
44 garbled display, but the system still boots to 44 garbled display, but the system still boots to completion. If you are
45 fortunate to have a driver that does not alter 45 fortunate to have a driver that does not alter the graphics chip, then you
46 will still get a VGA console. 46 will still get a VGA console.
47 47
48 B. Loading 48 B. Loading
49 ========== 49 ==========
50 50
51 Possible scenarios: 51 Possible scenarios:
52 52
53 1. Driver and fbcon are compiled statically 53 1. Driver and fbcon are compiled statically
54 54
55 Usually, fbcon will automatically tak 55 Usually, fbcon will automatically take over your console. The notable
56 exception is vesafb. It needs to be 56 exception is vesafb. It needs to be explicitly activated with the
57 vga= boot option parameter. 57 vga= boot option parameter.
58 58
59 2. Driver is compiled statically, fbcon is com 59 2. Driver is compiled statically, fbcon is compiled as a module
60 60
61 Depending on the driver, you either g 61 Depending on the driver, you either get a standard console, or a
62 garbled display, as mentioned above. 62 garbled display, as mentioned above. To get a framebuffer console,
63 do a 'modprobe fbcon'. 63 do a 'modprobe fbcon'.
64 64
65 3. Driver is compiled as a module, fbcon is co 65 3. Driver is compiled as a module, fbcon is compiled statically
66 66
67 You get your standard console. Once 67 You get your standard console. Once the driver is loaded with
68 'modprobe xxxfb', fbcon automatically 68 'modprobe xxxfb', fbcon automatically takes over the console with
69 the possible exception of using the f 69 the possible exception of using the fbcon=map:n option. See below.
70 70
71 4. Driver and fbcon are compiled as a module. 71 4. Driver and fbcon are compiled as a module.
72 72
73 You can load them in any order. Once 73 You can load them in any order. Once both are loaded, fbcon will take
74 over the console. 74 over the console.
75 75
76 C. Boot options 76 C. Boot options
77 77
78 The framebuffer console has several, 78 The framebuffer console has several, largely unknown, boot options
79 that can change its behavior. 79 that can change its behavior.
80 80
81 1. fbcon=font:<name> 81 1. fbcon=font:<name>
82 82
83 Select the initial font to use. The va 83 Select the initial font to use. The value 'name' can be any of the
84 compiled-in fonts: 10x18, 6x10, 6x8, 7 !! 84 compiled-in fonts: 10x18, 6x10, 7x14, Acorn8x8, MINI4x6,
85 PEARL8x8, ProFont6x11, SUN12x22, SUN8x 85 PEARL8x8, ProFont6x11, SUN12x22, SUN8x16, TER16x32, VGA8x16, VGA8x8.
86 86
87 Note, not all drivers can handle font 87 Note, not all drivers can handle font with widths not divisible by 8,
88 such as vga16fb. 88 such as vga16fb.
89 89
>> 90 2. fbcon=scrollback:<value>[k]
90 91
91 2. fbcon=map:<0123> !! 92 The scrollback buffer is memory that is used to preserve display
>> 93 contents that has already scrolled past your view. This is accessed
>> 94 by using the Shift-PageUp key combination. The value 'value' is any
>> 95 integer. It defaults to 32KB. The 'k' suffix is optional, and will
>> 96 multiply the 'value' by 1024.
>> 97
>> 98 3. fbcon=map:<0123>
92 99
93 This is an interesting option. It tell 100 This is an interesting option. It tells which driver gets mapped to
94 which console. The value '0123' is a s 101 which console. The value '0123' is a sequence that gets repeated until
95 the total length is 64 which is the nu 102 the total length is 64 which is the number of consoles available. In
96 the above example, it is expanded to 0 103 the above example, it is expanded to 012301230123... and the mapping
97 will be:: 104 will be::
98 105
99 tty | 1 2 3 4 5 6 7 8 9 ... 106 tty | 1 2 3 4 5 6 7 8 9 ...
100 fb | 0 1 2 3 0 1 2 3 0 ... 107 fb | 0 1 2 3 0 1 2 3 0 ...
101 108
102 ('cat /proc/fb' should tell yo 109 ('cat /proc/fb' should tell you what the fb numbers are)
103 110
104 One side effect that may be useful is 111 One side effect that may be useful is using a map value that exceeds
105 the number of loaded fb drivers. For e 112 the number of loaded fb drivers. For example, if only one driver is
106 available, fb0, adding fbcon=map:1 tel 113 available, fb0, adding fbcon=map:1 tells fbcon not to take over the
107 console. 114 console.
108 115
109 Later on, when you want to map the con 116 Later on, when you want to map the console the to the framebuffer
110 device, you can use the con2fbmap util 117 device, you can use the con2fbmap utility.
111 118
112 3. fbcon=vc:<n1>-<n2> !! 119 4. fbcon=vc:<n1>-<n2>
113 120
114 This option tells fbcon to take over o 121 This option tells fbcon to take over only a range of consoles as
115 specified by the values 'n1' and 'n2'. 122 specified by the values 'n1' and 'n2'. The rest of the consoles
116 outside the given range will still be 123 outside the given range will still be controlled by the standard
117 console driver. 124 console driver.
118 125
119 NOTE: For x86 machines, the standard c 126 NOTE: For x86 machines, the standard console is the VGA console which
120 is typically located on the same video 127 is typically located on the same video card. Thus, the consoles that
121 are controlled by the VGA console will 128 are controlled by the VGA console will be garbled.
122 129
123 4. fbcon=rotate:<n> !! 130 5. fbcon=rotate:<n>
124 131
125 This option changes the orientation an 132 This option changes the orientation angle of the console display. The
126 value 'n' accepts the following: 133 value 'n' accepts the following:
127 134
128 - 0 - normal orientation (0 degree 135 - 0 - normal orientation (0 degree)
129 - 1 - clockwise orientation (90 de 136 - 1 - clockwise orientation (90 degrees)
130 - 2 - upside down orientation (180 137 - 2 - upside down orientation (180 degrees)
131 - 3 - counterclockwise orientation 138 - 3 - counterclockwise orientation (270 degrees)
132 139
133 The angle can be changed anytime after 140 The angle can be changed anytime afterwards by 'echoing' the same
134 numbers to any one of the 2 attributes 141 numbers to any one of the 2 attributes found in
135 /sys/class/graphics/fbcon: 142 /sys/class/graphics/fbcon:
136 143
137 - rotate - rotate the disp 144 - rotate - rotate the display of the active console
138 - rotate_all - rotate the disp 145 - rotate_all - rotate the display of all consoles
139 146
140 Console rotation will only become avai 147 Console rotation will only become available if Framebuffer Console
141 Rotation support is compiled in your k 148 Rotation support is compiled in your kernel.
142 149
143 NOTE: This is purely console rotation. 150 NOTE: This is purely console rotation. Any other applications that
144 use the framebuffer will remain at the 151 use the framebuffer will remain at their 'normal' orientation.
145 Actually, the underlying fb driver is 152 Actually, the underlying fb driver is totally ignorant of console
146 rotation. 153 rotation.
147 154
148 5. fbcon=margin:<color> !! 155 6. fbcon=margin:<color>
149 156
150 This option specifies the color of the 157 This option specifies the color of the margins. The margins are the
151 leftover area at the right and the bot 158 leftover area at the right and the bottom of the screen that are not
152 used by text. By default, this area wi 159 used by text. By default, this area will be black. The 'color' value
153 is an integer number that depends on t 160 is an integer number that depends on the framebuffer driver being used.
154 161
155 6. fbcon=nodefer !! 162 7. fbcon=nodefer
156 163
157 If the kernel is compiled with deferre 164 If the kernel is compiled with deferred fbcon takeover support, normally
158 the framebuffer contents, left in plac 165 the framebuffer contents, left in place by the firmware/bootloader, will
159 be preserved until there actually is s 166 be preserved until there actually is some text is output to the console.
160 This option causes fbcon to bind immed 167 This option causes fbcon to bind immediately to the fbdev device.
161 168
162 7. fbcon=logo-pos:<location> !! 169 8. fbcon=logo-pos:<location>
163 170
164 The only possible 'location' is 'cente 171 The only possible 'location' is 'center' (without quotes), and when
165 given, the bootup logo is moved from t 172 given, the bootup logo is moved from the default top-left corner
166 location to the center of the framebuf 173 location to the center of the framebuffer. If more than one logo is
167 displayed due to multiple CPUs, the co 174 displayed due to multiple CPUs, the collected line of logos is moved
168 as a whole. 175 as a whole.
169 176
170 8. fbcon=logo-count:<n> !! 177 9. fbcon=logo-count:<n>
171 178
172 The value 'n' overrides the number of 179 The value 'n' overrides the number of bootup logos. 0 disables the
173 logo, and -1 gives the default which i 180 logo, and -1 gives the default which is the number of online CPUs.
174 181
175 C. Attaching, Detaching and Unloading 182 C. Attaching, Detaching and Unloading
176 183
177 Before going on to how to attach, detach and u 184 Before going on to how to attach, detach and unload the framebuffer console, an
178 illustration of the dependencies may help. 185 illustration of the dependencies may help.
179 186
180 The console layer, as with most subsystems, ne 187 The console layer, as with most subsystems, needs a driver that interfaces with
181 the hardware. Thus, in a VGA console:: 188 the hardware. Thus, in a VGA console::
182 189
183 console ---> VGA driver ---> hardware. 190 console ---> VGA driver ---> hardware.
184 191
185 Assuming the VGA driver can be unloaded, one m 192 Assuming the VGA driver can be unloaded, one must first unbind the VGA driver
186 from the console layer before unloading the dr 193 from the console layer before unloading the driver. The VGA driver cannot be
187 unloaded if it is still bound to the console l 194 unloaded if it is still bound to the console layer. (See
188 Documentation/driver-api/console.rst for more 195 Documentation/driver-api/console.rst for more information).
189 196
190 This is more complicated in the case of the fr 197 This is more complicated in the case of the framebuffer console (fbcon),
191 because fbcon is an intermediate layer between 198 because fbcon is an intermediate layer between the console and the drivers::
192 199
193 console ---> fbcon ---> fbdev drivers 200 console ---> fbcon ---> fbdev drivers ---> hardware
194 201
195 The fbdev drivers cannot be unloaded if bound 202 The fbdev drivers cannot be unloaded if bound to fbcon, and fbcon cannot
196 be unloaded if it's bound to the console layer 203 be unloaded if it's bound to the console layer.
197 204
198 So to unload the fbdev drivers, one must first 205 So to unload the fbdev drivers, one must first unbind fbcon from the console,
199 then unbind the fbdev drivers from fbcon. For 206 then unbind the fbdev drivers from fbcon. Fortunately, unbinding fbcon from
200 the console layer will automatically unbind fr 207 the console layer will automatically unbind framebuffer drivers from
201 fbcon. Thus, there is no need to explicitly un 208 fbcon. Thus, there is no need to explicitly unbind the fbdev drivers from
202 fbcon. 209 fbcon.
203 210
204 So, how do we unbind fbcon from the console? P 211 So, how do we unbind fbcon from the console? Part of the answer is in
205 Documentation/driver-api/console.rst. To summa 212 Documentation/driver-api/console.rst. To summarize:
206 213
207 Echo a value to the bind file that represents 214 Echo a value to the bind file that represents the framebuffer console
208 driver. So assuming vtcon1 represents fbcon, t 215 driver. So assuming vtcon1 represents fbcon, then::
209 216
210 echo 1 > /sys/class/vtconsole/vtcon1/bind - !! 217 echo 1 > sys/class/vtconsole/vtcon1/bind - attach framebuffer console to
211 c 218 console layer
212 echo 0 > /sys/class/vtconsole/vtcon1/bind - !! 219 echo 0 > sys/class/vtconsole/vtcon1/bind - detach framebuffer console from
213 c 220 console layer
214 221
215 If fbcon is detached from the console layer, y 222 If fbcon is detached from the console layer, your boot console driver (which is
216 usually VGA text mode) will take over. A few 223 usually VGA text mode) will take over. A few drivers (rivafb and i810fb) will
217 restore VGA text mode for you. With the rest, 224 restore VGA text mode for you. With the rest, before detaching fbcon, you
218 must take a few additional steps to make sure 225 must take a few additional steps to make sure that your VGA text mode is
219 restored properly. The following is one of the 226 restored properly. The following is one of the several methods that you can do:
220 227
221 1. Download or install vbetool. This utility 228 1. Download or install vbetool. This utility is included with most
222 distributions nowadays, and is usually part 229 distributions nowadays, and is usually part of the suspend/resume tool.
223 230
224 2. In your kernel configuration, ensure that C 231 2. In your kernel configuration, ensure that CONFIG_FRAMEBUFFER_CONSOLE is set
225 to 'y' or 'm'. Enable one or more of your f 232 to 'y' or 'm'. Enable one or more of your favorite framebuffer drivers.
226 233
227 3. Boot into text mode and as root run:: 234 3. Boot into text mode and as root run::
228 235
229 vbetool vbestate save > <vga state fil 236 vbetool vbestate save > <vga state file>
230 237
231 The above command saves the register conten 238 The above command saves the register contents of your graphics
232 hardware to <vga state file>. You need to 239 hardware to <vga state file>. You need to do this step only once as
233 the state file can be reused. 240 the state file can be reused.
234 241
235 4. If fbcon is compiled as a module, load fbco 242 4. If fbcon is compiled as a module, load fbcon by doing::
236 243
237 modprobe fbcon 244 modprobe fbcon
238 245
239 5. Now to detach fbcon:: 246 5. Now to detach fbcon::
240 247
241 vbetool vbestate restore < <vga state f 248 vbetool vbestate restore < <vga state file> && \
242 echo 0 > /sys/class/vtconsole/vtcon1/bi 249 echo 0 > /sys/class/vtconsole/vtcon1/bind
243 250
244 6. That's it, you're back to VGA mode. And if 251 6. That's it, you're back to VGA mode. And if you compiled fbcon as a module,
245 you can unload it by 'rmmod fbcon'. 252 you can unload it by 'rmmod fbcon'.
246 253
247 7. To reattach fbcon:: 254 7. To reattach fbcon::
248 255
249 echo 1 > /sys/class/vtconsole/vtcon1/bi 256 echo 1 > /sys/class/vtconsole/vtcon1/bind
250 257
251 8. Once fbcon is unbound, all drivers register 258 8. Once fbcon is unbound, all drivers registered to the system will also
252 become unbound. This means that fbcon and ind 259 become unbound. This means that fbcon and individual framebuffer drivers
253 can be unloaded or reloaded at will. Reloading 260 can be unloaded or reloaded at will. Reloading the drivers or fbcon will
254 automatically bind the console, fbcon and the 261 automatically bind the console, fbcon and the drivers together. Unloading
255 all the drivers without unloading fbcon will m 262 all the drivers without unloading fbcon will make it impossible for the
256 console to bind fbcon. 263 console to bind fbcon.
257 264
258 Notes for vesafb users: 265 Notes for vesafb users:
259 ======================= 266 =======================
260 267
261 Unfortunately, if your bootline includes a vga 268 Unfortunately, if your bootline includes a vga=xxx parameter that sets the
262 hardware in graphics mode, such as when loadin 269 hardware in graphics mode, such as when loading vesafb, vgacon will not load.
263 Instead, vgacon will replace the default boot 270 Instead, vgacon will replace the default boot console with dummycon, and you
264 won't get any display after detaching fbcon. Y 271 won't get any display after detaching fbcon. Your machine is still alive, so
265 you can reattach vesafb. However, to reattach 272 you can reattach vesafb. However, to reattach vesafb, you need to do one of
266 the following: 273 the following:
267 274
268 Variation 1: 275 Variation 1:
269 276
270 a. Before detaching fbcon, do:: 277 a. Before detaching fbcon, do::
271 278
272 vbetool vbemode save > <vesa state fil 279 vbetool vbemode save > <vesa state file> # do once for each vesafb mode,
273 280 # the file can be reused
274 281
275 b. Detach fbcon as in step 5. 282 b. Detach fbcon as in step 5.
276 283
277 c. Attach fbcon:: 284 c. Attach fbcon::
278 285
279 vbetool vbestate restore < <vesa state 286 vbetool vbestate restore < <vesa state file> && \
280 echo 1 > /sys/class/vtconsole/vtcon1/b 287 echo 1 > /sys/class/vtconsole/vtcon1/bind
281 288
282 Variation 2: 289 Variation 2:
283 290
284 a. Before detaching fbcon, do:: 291 a. Before detaching fbcon, do::
285 292
286 echo <ID> > /sys/class/tty/console/bin 293 echo <ID> > /sys/class/tty/console/bind
287 294
288 vbetool vbemode get 295 vbetool vbemode get
289 296
290 b. Take note of the mode number 297 b. Take note of the mode number
291 298
292 b. Detach fbcon as in step 5. 299 b. Detach fbcon as in step 5.
293 300
294 c. Attach fbcon:: 301 c. Attach fbcon::
295 302
296 vbetool vbemode set <mode number> && \ 303 vbetool vbemode set <mode number> && \
297 echo 1 > /sys/class/vtconsole/vtcon1/b 304 echo 1 > /sys/class/vtconsole/vtcon1/bind
298 305
299 Samples: 306 Samples:
300 ======== 307 ========
301 308
302 Here are 2 sample bash scripts that you can us 309 Here are 2 sample bash scripts that you can use to bind or unbind the
303 framebuffer console driver if you are on an X8 310 framebuffer console driver if you are on an X86 box::
304 311
305 #!/bin/bash 312 #!/bin/bash
306 # Unbind fbcon 313 # Unbind fbcon
307 314
308 # Change this to where your actual vgastate 315 # Change this to where your actual vgastate file is located
309 # Or Use VGASTATE=$1 to indicate the state f 316 # Or Use VGASTATE=$1 to indicate the state file at runtime
310 VGASTATE=/tmp/vgastate 317 VGASTATE=/tmp/vgastate
311 318
312 # path to vbetool 319 # path to vbetool
313 VBETOOL=/usr/local/bin 320 VBETOOL=/usr/local/bin
314 321
315 322
316 for (( i = 0; i < 16; i++)) 323 for (( i = 0; i < 16; i++))
317 do 324 do
318 if test -x /sys/class/vtconsole/vtcon$i; t 325 if test -x /sys/class/vtconsole/vtcon$i; then
319 if [ `cat /sys/class/vtconsole/vtcon$i 326 if [ `cat /sys/class/vtconsole/vtcon$i/name | grep -c "frame buffer"` \
320 = 1 ]; then 327 = 1 ]; then
321 if test -x $VBETOOL/vbetool; then 328 if test -x $VBETOOL/vbetool; then
322 echo Unbinding vtcon$i 329 echo Unbinding vtcon$i
323 $VBETOOL/vbetool vbestate resto 330 $VBETOOL/vbetool vbestate restore < $VGASTATE
324 echo 0 > /sys/class/vtconsole/v 331 echo 0 > /sys/class/vtconsole/vtcon$i/bind
325 fi 332 fi
326 fi 333 fi
327 fi 334 fi
328 done 335 done
329 336
330 ---------------------------------------------- 337 ---------------------------------------------------------------------------
331 338
332 :: 339 ::
333 340
334 #!/bin/bash 341 #!/bin/bash
335 # Bind fbcon 342 # Bind fbcon
336 343
337 for (( i = 0; i < 16; i++)) 344 for (( i = 0; i < 16; i++))
338 do 345 do
339 if test -x /sys/class/vtconsole/vtcon$i; t 346 if test -x /sys/class/vtconsole/vtcon$i; then
340 if [ `cat /sys/class/vtconsole/vtcon$i 347 if [ `cat /sys/class/vtconsole/vtcon$i/name | grep -c "frame buffer"` \
341 = 1 ]; then 348 = 1 ]; then
342 echo Unbinding vtcon$i 349 echo Unbinding vtcon$i
343 echo 1 > /sys/class/vtconsole/vtcon$ 350 echo 1 > /sys/class/vtconsole/vtcon$i/bind
344 fi 351 fi
345 fi 352 fi
346 done 353 done
347 354
348 Antonino Daplas <adaplas@pol.net> 355 Antonino Daplas <adaplas@pol.net>
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