[PATCH] Detaching fbcon: update documentation

	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.

	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>