[PATCH] Detaching fbcon: update documentation

Update Documentation/fb/fbcon.txt on the following:

1. sysfs attributes are now located in class/graphics/fbcon
2. instructions on how to attach, detach and/or unload fbcon

Signed-off-by: Antonino Daplas <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Antonino A. Daplas 2006-06-26 00:27:07 -07:00 committed by Linus Torvalds
parent 5428b04405
commit a4a73e1f02
1 changed files with 100 additions and 4 deletions

View File

@ -135,10 +135,10 @@ C. Boot options
The angle can be changed anytime afterwards by 'echoing' the same
numbers to any one of the 2 attributes found in
/sys/class/graphics/fb{x}
/sys/class/graphics/fbcon
con_rotate - rotate the display of the active console
con_rotate_all - rotate the display of all consoles
rotate - rotate the display of the active console
rotate_all - rotate the display of all consoles
Console rotation will only become available if Console Rotation
Support is compiled in your kernel.
@ -148,5 +148,101 @@ C. Boot options
Actually, the underlying fb driver is totally ignorant of console
rotation.
---
C. Attaching, Detaching and Unloading
It's possible to detach/attach the framebuffer console from the vt layer by
echoing anything to the following sysfs attributes found
/sys/class/graphics/fbcon.
attach - attach framebuffer console to vt layer
detach - detach framebuffer console to vt layer
If fbcon is detached from the vt 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 1 > /sys/class/graphics/fbcon/detach
6. That's it, you're back to VGA mode. And if you compiled your drivers as
modules, you can unload them at will. So if you want to change your driver
from xxxfb to yyyfb, you can do this:
detach fbcon
rmmod xxxfb
modprobe yyyfb
Of course, con2fbmap can do the same thing but will not work if xxxfb
and yyyfb are not compatible (ie, cannot be loaded at the same time).
7. To reattach fbcon:
echo 1 > /sys/class/graphics/fbcon/attach
8. Once the framebuffer console is detached, and if it is compiled as a module,
the module can be unloaded with 'rmmod fbcon'. This feature is great for
developers.
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/graphics/fbcon/attach
Variation 2:
a. Before detaching fbcon, do:
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/graphics/fbcon/attach
--
Antonino Daplas <adaplas@pol.net>