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 <[email protected]>
---
Documentation/fb/fbcon.txt | 104 ++++++++++++++++++++++++++++++++++++++++++--
1 files changed, 100 insertions(+), 4 deletions(-)
diff --git a/Documentation/fb/fbcon.txt b/Documentation/fb/fbcon.txt
index 08dce0f..f3a3be0 100644
--- a/Documentation/fb/fbcon.txt
+++ b/Documentation/fb/fbcon.txt
@@ -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 <[email protected]>
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