+C. Attaching, Detaching and Unloading
+
+Before going on on how to attach, detach and unload the framebuffer console, an
+illustration of the dependencies may help.
+
+The console layer, as with most subsystems, needs a driver that interfaces with
+the hardware. Thus, in a VGA console:
+
+console ---> VGA driver ---> hardware.
+
+Assuming the VGA driver can be unloaded, one must first unbind the VGA driver
+from the console layer before unloading the driver. The VGA driver cannot be
+unloaded if it is still bound to the console layer. (See
+Documentation/console/console.txt for more information).
+
+This is more complicated in the case of the framebuffer console (fbcon),
+because fbcon is an intermediate layer between the console and the drivers:
+
+console ---> fbcon ---> fbdev drivers ---> hardware
+
+The fbdev drivers cannot be unloaded if it's bound to fbcon, and fbcon cannot
+be unloaded if it's bound to the console layer.
+
+So to unload the fbdev drivers, one must first unbind fbcon from the console,
+then unbind the fbdev drivers from fbcon. Fortunately, unbinding fbcon from
+the console layer will automatically unbind framebuffer drivers from
+fbcon. Thus, there is no need to explicitly unbind the fbdev drivers from
+fbcon.
+
+So, how do we unbind fbcon from the console? Part of the answer is in
+Documentation/console/console.txt. To summarize:
+
+Echo a value to the bind file that represents the framebuffer console
+driver. So assuming vtcon1 represents fbcon, then:
+
+echo 1 > sys/class/vtconsole/vtcon1/bind - attach framebuffer console to
+ console layer
+echo 0 > sys/class/vtconsole/vtcon1/bind - detach framebuffer console from
+ console layer
+
+If fbcon is detached from the console layer, your boot console driver (which is
+usually VGA text mode) will take over. A few drivers (rivafb and i810fb) will
+restore VGA text mode for you. With the rest, before detaching fbcon, you
+must take a few additional steps to make sure that your VGA text mode is
+restored properly. The following is one of the several methods that you can do:
+
+1. Download or install vbetool. This utility is included with most
+ distributions nowadays, and is usually part of the suspend/resume tool.
+
+2. In your kernel configuration, ensure that CONFIG_FRAMEBUFFER_CONSOLE is set
+ to 'y' or 'm'. Enable one or more of your favorite framebuffer drivers.
+
+3. Boot into text mode and as root run:
+
+ vbetool vbestate save > <vga state file>
+
+ The above command saves the register contents of your graphics
+ hardware to <vga state file>. You need to do this step only once as
+ the state file can be reused.
+
+4. If fbcon is compiled as a module, load fbcon by doing:
+
+ modprobe fbcon
+
+5. Now to detach fbcon:
+
+ vbetool vbestate restore < <vga state file> && \
+ echo 0 > /sys/class/vtconsole/vtcon1/bind
+
+6. That's it, you're back to VGA mode. And if you compiled fbcon as a module,
+ you can unload it by 'rmmod fbcon'
+
+7. To reattach fbcon:
+
+ echo 1 > /sys/class/vtconsole/vtcon1/bind
+
+8. Once fbcon is unbound, all drivers registered to the system will also
+become unbound. This means that fbcon and individual framebuffer drivers
+can be unloaded or reloaded at will. Reloading the drivers or fbcon will
+automatically bind the console, fbcon and the drivers together. Unloading
+all the drivers without unloading fbcon will make it impossible for the
+console to bind fbcon.
+
+Notes for vesafb users:
+=======================
+
+Unfortunately, if your bootline includes a vga=xxx parameter that sets the
+hardware in graphics mode, such as when loading vesafb, vgacon will not load.
+Instead, vgacon will replace the default boot console with dummycon, and you
+won't get any display after detaching fbcon. Your machine is still alive, so
+you can reattach vesafb. However, to reattach vesafb, you need to do one of
+the following:
+
+Variation 1:
+
+ a. Before detaching fbcon, do
+
+ vbetool vbemode save > <vesa state file> # do once for each vesafb mode,
+ # the file can be reused
+
+ b. Detach fbcon as in step 5.
+
+ c. Attach fbcon
+
+ vbetool vbestate restore < <vesa state file> && \
+ echo 1 > /sys/class/vtconsole/vtcon1/bind
+
+Variation 2:
+
+ a. Before detaching fbcon, do:
+ echo <ID> > /sys/class/tty/console/bind
+
+
+ vbetool vbemode get
+
+ b. Take note of the mode number
+
+ b. Detach fbcon as in step 5.
+
+ c. Attach fbcon:
+
+ vbetool vbemode set <mode number> && \
+ echo 1 > /sys/class/vtconsole/vtcon1/bind
+
+Samples:
+========
+
+Here are 2 sample bash scripts that you can use to bind or unbind the
+framebuffer console driver if you are in an X86 box:
+
+---------------------------------------------------------------------------
+#!/bin/bash
+# Unbind fbcon
+
+# Change this to where your actual vgastate file is located
+# Or Use VGASTATE=$1 to indicate the state file at runtime
+VGASTATE=/tmp/vgastate
+
+# path to vbetool
+VBETOOL=/usr/local/bin
+
+
+for (( i = 0; i < 16; i++))
+do
+ if test -x /sys/class/vtconsole/vtcon$i; then
+ if [ `cat /sys/class/vtconsole/vtcon$i/name | grep -c "frame buffer"` \
+ = 1 ]; then
+ if test -x $VBETOOL/vbetool; then
+ echo Unbinding vtcon$i
+ $VBETOOL/vbetool vbestate restore < $VGASTATE
+ echo 0 > /sys/class/vtconsole/vtcon$i/bind
+ fi
+ fi
+ fi
+done
+
+---------------------------------------------------------------------------
+#!/bin/bash
+# Bind fbcon
+
+for (( i = 0; i < 16; i++))
+do
+ if test -x /sys/class/vtconsole/vtcon$i; then
+ if [ `cat /sys/class/vtconsole/vtcon$i/name | grep -c "frame buffer"` \
+ = 1 ]; then
+ echo Unbinding vtcon$i
+ echo 1 > /sys/class/vtconsole/vtcon$i/bind
+ fi
+ fi
+done
+---------------------------------------------------------------------------
+
+--
git://git.onelab.eu / linux-2.6.git / blobdiff