diff options
| -rw-r--r-- | Documentation/fb/fbcon.txt | 73 |
1 files changed, 50 insertions, 23 deletions
diff --git a/Documentation/fb/fbcon.txt b/Documentation/fb/fbcon.txt index f3a3be087707..b91aea57a98e 100644 --- a/Documentation/fb/fbcon.txt +++ b/Documentation/fb/fbcon.txt @@ -150,14 +150,42 @@ C. Boot options 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. +Before going on on how to attach, detach and unload the framebuffer console, an +illustration of the dependencies may help. - attach - attach framebuffer console to vt layer - detach - detach framebuffer console to vt layer +The console layer, as with most subsystems, needs a driver that interfaces with +the hardware. Thus, in a VGA console: -If fbcon is detached from the vt layer, your boot console driver (which is +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 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 it's 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 the ID number of the 'frame buffer driver' to: + +sys/class/tty/console/bind - attach framebuffer console to console layer +sys/class/tty/console/unbind - 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 @@ -183,27 +211,26 @@ restored properly. The following is one of the several methods that you can do: 5. Now to detach fbcon: - vbetool vbestate restore < <vga state file> && \ - echo 1 > /sys/class/graphics/fbcon/detach + 'cat /sys/class/tty/console/backend' and take note of the ID -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: +The above is probably needed only once. Then: - detach fbcon - rmmod xxxfb - modprobe yyyfb + vbetool vbestate restore < <vga state file> && \ + echo <ID> > /sys/class/tty/console/unbind - 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). +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/graphics/fbcon/attach + echo <ID> > /sys/class/tty/console/bind -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. +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: ======================= @@ -227,11 +254,11 @@ Variation 1: c. Attach fbcon vbetool vbestate restore < <vesa state file> && \ - echo 1 > /sys/class/graphics/fbcon/attach - Variation 2: a. Before detaching fbcon, do: + echo <ID> > /sys/class/tty/console/bind + vbetool vbemode get @@ -242,7 +269,7 @@ Variation 2: c. Attach fbcon: vbetool vbemode set <mode number> && \ - echo 1 > /sys/class/graphics/fbcon/attach + echo <ID> > /sys/class/tty/console/bind -- Antonino Daplas <adaplas@pol.net> |