From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Antonino A. Daplas" Subject: Re: [PATCH 6/7] Detaching fbcon: Add capability to attach/detach fbcon Date: Wed, 07 Jun 2006 07:17:14 +0800 Message-ID: <44860CFA.4040409@gmail.com> References: <4485624C.9070707@gmail.com> <20060606151210.22751bce.akpm@osdl.org> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20060606151210.22751bce.akpm@osdl.org> Sender: linux-kernel-owner@vger.kernel.org List-Id: Cc: linux-fbdev-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org Andrew Morton wrote: > On Tue, 06 Jun 2006 19:09:00 +0800 > "Antonino A. Daplas" 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