Andrew Morton wrote:
> On Tue, 06 Jun 2006 19:09:00 +0800
> "Antonino A. Daplas" <[email protected]> wrote:
>
>> Add the ability to detach and attach the framebuffer console to and from
>> the vt layer. This is done by echo'ing any value to sysfs attributes located
>> in class/graphics/fbcon. The two attributes are:
>>
>> attach - bind fbcon to the vt layer
>> detach - unbind fbcon from the vt layer
>
> That's a bit unusual. Normally a bind or unbind operation will operate
> primarily upon the thing which is bound to, not upon the thing which is
> bound.
I'm not against this.
>
> I assume it makes sense this way, given the way the vt layer operates. But
> it rather rules out binding the fbcon layer to anything apart from the vt
> layer (just thinking about it design-wise).
The vt-layer is different in that the device themselves bind to it, not
the other way around. As I've told Jon, if someone change the vt-layer so
it behaves in a standard way, I'm all for it (that someone is probably me).
But thinking about it, it is probably not very difficult to change the
vt-layer. We just make the vt-layer keep a list of registered drivers. And
we already have /sys/class/tty/console, so I can put the attribute there
for bind and unbind.
>
> ummm, expressing it differently:
>
> echo "bind fbcon" > /sys/whatever/some-vt-file
> echo "unbind fbcon" > /sys/whatever/some-vt-file
>
> would be more typical usage.
>
>> Once fbcon is detached from the vt layer, fbcon can be unloaded if compiled as
>> a module. This feature is quite useful for developers who work on the
>> framebuffer or console subsystem. This is also useful for users who want to
>> go to text mode or graphics mode without having to reboot.
>
> Do we have a place where this can be documented?
In Documentation/fb/fbcon.txt.
>
>> Directly unloading the fbcon module is not possible because the vt layer
>> increments the module reference count for all bound consoles. Detaching fbcon
>> decrements the module reference count to zero so unloading becomes possible.
>
> Right. So the vt layer should be told to let go of the fbcon layer. It's
> a vt operation, not an fbcon one, yes?
Yes. I'll take a stab at doing it this way.
Tony
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