Re: [Linux-fbdev-devel] [PATCH] FBDev: vga16fb port

[Sven Luther]

On Wed, Dec 04, 2002 at 05:08:53PM +0500, Antonino Daplas wrote:
> On Wed, 2002-12-04 at 12:32, Sven Luther wrote:
> > On Tue, Dec 03, 2002 at 05:22:35PM +0500, Antonino Daplas wrote:
> > > >   2) The ability to go back to vga text mode on close of /dev/fb. 
> > > >      Yes fbdev/fbcon supports that now. 
> > > 
> > > I'll take a stab at writing VGA save/restore routines which hopefully is
> > > generic enough to be used by various hardware.  No promises though, VGA
> > > programming gives me a headache :(
> > 
> > BTW, i am writing a fbdev for a card where the docs tell me to disable
> > vga output before enabling graphical output. Does i need to do this in
> > the fbdev i write, or is it already handled by the vga layer, or
> > whatever ?
> 
> Most cards with a VGA core needs to disable the VGA output before going
> to graphics mode.  Disabling VGA output is hardware specific, and is
> usually automatic when you go to graphics mode.

So there is no common zqy of doing this, my docs say something about a
vga control register zhich is accesses trough the sequencer regs. Does
vgafb (or textmode or whatever) not call this when giving the hand to
the fbdev ?

> Because James wrote the fb framework to be very modular, then you must
> be careful to save/restore the initial video state  when loading or
> unloading.  Theoretically, a driver should load, but not go to graphics
> mode immediately.  Only upon a call to xxxfb_set_par() should the driver
> do so.  Before going to graphics mode, that's were you save the initial
> state.  Have a reference count or something to keep track of the number
> of users, and when this reference count becomes zero, restore the
> initial state.  You should be able to do this by hooking these routines
> in fb_open() and fb_release().

Mmm, what about interaction with X ? X also does a save/restore of the
previous (text) mode, when a X driver is _not_ fbdev aware, it will
save/restore the things twice, right ?

> The one I submitted (and a revised one I'm going to submit soon) should
> be able to restore the VGA text/graphics mode.  Complement this with
> your hardware's extended state save and restore routines and you should
> be able to load/use/unload your driver repeatedly :-).

Ok, i will try.

Friendlmy

Sven Luther