[Intel-gfx] [PATCH i-g-t] lib/sysfs: Fix fbcon rebind

[Daniel Vetter]

On Wed, Sep 06, 2017 at 05:34:45PM +0300, Ville Syrjälä wrote:
> On Wed, Sep 06, 2017 at 03:08:40PM +0100, Chris Wilson wrote:
> > Quoting ville.syrjala at linux.intel.com (2017-09-06 14:04:01)
> > > From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > > 
> > > "echo 1 > vtconN/bind" doesn't actually do anything. Looks like the only
> > > way to rebind fbcon is to unbind the current console.
> > > 
> > > I suppose the failure to rebind might be a kernel bug, but I can't be
> > > bothered to decode the vt.c spaghetti so let's just try to handle this
> > > in igt. For simplicity let's assume the currently bound console is the
> > > dummy console and unbind that when we want to rebind fbcon. That works
> > > for me.
> > > 
> > > With rebinding not working we can't really tell wich console is going
> > > to get bound anyway, so there's no way to make this code really robust,
> > > assuming we ever had more than these two console drivers involved.
> > 
> > Hmm, CONFIG_DUMMY_CONSOLE suggests that the dummy isn't universal
> > either. If there is no dummy, can the last be unbound? I have no idea.
> 
> DUMMY_CONSOLE isn't user visible and default=y, so you can't actually
> disable it, I think.
> 
> It does have some suspicious looking dependencies though:
>  depends on VGA_CONSOLE!=y || SGI_NEWPORT_CONSOLE!=y 
> 
> So it gets disabled only if you have both VGA and SGI_NEWPORT enabled.
> I suspect someone meant to say '&&' instead of '||'. But for us the '||'
> works better since we don't allow rebinding vgacon after it's been
> kicked out, and so having dummy+vga is good.

We select the dummy con in i915, to be able to kick out vgacon before we
register fbdev. So should always be there.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch