Adding upstream version 4.19.249.upstream/4.19.249

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 339 insertions, 0 deletions

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+The Framebuffer Console
+=======================
+
+	The framebuffer console (fbcon), as its name implies, is a text
+console running on top of the framebuffer device. It has the functionality of
+any standard text console driver, such as the VGA console, with the added
+features that can be attributed to the graphical nature of the framebuffer.
+
+	 In the x86 architecture, the framebuffer console is optional, and
+some even treat it as a toy. For other architectures, it is the only available
+display device, text or graphical.
+
+	 What are the features of fbcon?  The framebuffer console supports
+high resolutions, varying font types, display rotation, primitive multihead,
+etc. Theoretically, multi-colored fonts, blending, aliasing, and any feature
+made available by the underlying graphics card are also possible.
+
+A. Configuration
+
+	The framebuffer console can be enabled by using your favorite kernel
+configuration tool.  It is under Device Drivers->Graphics Support->Frame
+buffer Devices->Console display driver support->Framebuffer Console Support.
+Select 'y' to compile support statically or 'm' for module support.  The
+module will be fbcon.
+
+	In order for fbcon to activate, at least one framebuffer driver is
+required, so choose from any of the numerous drivers available. For x86
+systems, they almost universally have VGA cards, so vga16fb and vesafb will
+always be available. However, using a chipset-specific driver will give you
+more speed and features, such as the ability to change the video mode
+dynamically.
+
+	To display the penguin logo, choose any logo available in Graphics
+support->Bootup logo.
+
+	Also, you will need to select at least one compiled-in font, but if
+you don't do anything, the kernel configuration tool will select one for you,
+usually an 8x16 font.
+
+GOTCHA: A common bug report is enabling the framebuffer without enabling the
+framebuffer console.  Depending on the driver, you may get a blanked or
+garbled display, but the system still boots to completion.  If you are
+fortunate to have a driver that does not alter the graphics chip, then you
+will still get a VGA console.
+
+B. Loading
+
+Possible scenarios:
+
+1. Driver and fbcon are compiled statically
+
+	 Usually, fbcon will automatically take over your console. The notable
+	 exception is vesafb.  It needs to be explicitly activated with the
+	 vga= boot option parameter.
+
+2. Driver is compiled statically, fbcon is compiled as a module
+
+	 Depending on the driver, you either get a standard console, or a
+	 garbled display, as mentioned above.  To get a framebuffer console,
+	 do a 'modprobe fbcon'.
+
+3. Driver is compiled as a module, fbcon is compiled statically
+
+	 You get your standard console.  Once the driver is loaded with
+	 'modprobe xxxfb', fbcon automatically takes over the console with
+	 the possible exception of using the fbcon=map:n option. See below.
+
+4. Driver and fbcon are compiled as a module.
+
+	 You can load them in any order. Once both are loaded, fbcon will take
+	 over the console.
+
+C. Boot options
+
+         The framebuffer console has several, largely unknown, boot options
+         that can change its behavior.
+
+1. fbcon=font:<name>
+
+        Select the initial font to use. The value 'name' can be any of the
+        compiled-in fonts: 10x18, 6x10, 7x14, Acorn8x8, MINI4x6,
+        PEARL8x8, ProFont6x11, SUN12x22, SUN8x16, VGA8x16, VGA8x8.
+
+	Note, not all drivers can handle font with widths not divisible by 8,
+        such as vga16fb.
+
+2. fbcon=scrollback:<value>[k]
+
+        The scrollback buffer is memory that is used to preserve display
+        contents that has already scrolled past your view.  This is accessed
+        by using the Shift-PageUp key combination.  The value 'value' is any
+        integer. It defaults to 32KB.  The 'k' suffix is optional, and will
+        multiply the 'value' by 1024.
+
+3. fbcon=map:<0123>
+
+        This is an interesting option. It tells which driver gets mapped to
+        which console. The value '0123' is a sequence that gets repeated until
+        the total length is 64 which is the number of consoles available. In
+        the above example, it is expanded to 012301230123... and the mapping
+        will be:
+
+		tty | 1 2 3 4 5 6 7 8 9 ...
+		fb  | 0 1 2 3 0 1 2 3 0 ...
+
+		('cat /proc/fb' should tell you what the fb numbers are)
+
+	One side effect that may be useful is using a map value that exceeds
+	the number of loaded fb drivers. For example, if only one driver is
+	available, fb0, adding fbcon=map:1 tells fbcon not to take over the
+	console.
+
+	Later on, when you want to map the console the to the framebuffer
+	device, you can use the con2fbmap utility.
+
+4. fbcon=vc:<n1>-<n2>
+
+	This option tells fbcon to take over only a range of consoles as
+	specified by the values 'n1' and 'n2'. The rest of the consoles
+	outside the given range will still be controlled by the standard
+	console driver.
+
+	NOTE: For x86 machines, the standard console is the VGA console which
+	is typically located on the same video card.  Thus, the consoles that
+	are controlled by the VGA console will be garbled.
+
+4. fbcon=rotate:<n>
+
+        This option changes the orientation angle of the console display. The
+        value 'n' accepts the following:
+
+	      0 - normal orientation (0 degree)
+	      1 - clockwise orientation (90 degrees)
+	      2 - upside down orientation (180 degrees)
+	      3 - counterclockwise orientation (270 degrees)
+
+	The angle can be changed anytime afterwards by 'echoing' the same
+	numbers to any one of the 2 attributes found in
+	/sys/class/graphics/fbcon:
+
+		rotate     - rotate the display of the active console
+		rotate_all - rotate the display of all consoles
+
+	Console rotation will only become available if Framebuffer Console
+	Rotation support is compiled in your kernel.
+
+	NOTE: This is purely console rotation.  Any other applications that
+	use the framebuffer will remain at their 'normal' orientation.
+	Actually, the underlying fb driver is totally ignorant of console
+	rotation.
+
+5. fbcon=margin:<color>
+
+	This option specifies the color of the margins. The margins are the
+	leftover area at the right and the bottom of the screen that are not
+	used by text. By default, this area will be black. The 'color' value
+	is an integer number that depends on the framebuffer driver being used.
+
+6. fbcon=nodefer
+
+	If the kernel is compiled with deferred fbcon takeover support, normally
+	the framebuffer contents, left in place by the firmware/bootloader, will
+	be preserved until there actually is some text is output to the console.
+	This option causes fbcon to bind immediately to the fbdev device.
+
+C. Attaching, Detaching and Unloading
+
+Before going on to 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 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 on 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
+---------------------------------------------------------------------------
+
+--
+Antonino Daplas <adaplas@pol.net>