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Commit a4a73e1f authored by Antonino A. Daplas's avatar Antonino A. Daplas Committed by Linus Torvalds
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[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: default avatarAntonino Daplas <adaplas@pol.net>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 5428b044
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+100 −4
Original line number Diff line number Diff line
@@ -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>