Re: Console unregistration questions

["Antonino A. Daplas" <adaplas@gmail.com>]

On Tue, 2007-04-24 at 16:42 -0700, Jesse Barnes wrote:
> On Tuesday, April 24, 2007, Antonino A. Daplas wrote:
> > > But since we're using drmfb as a console, the unregister_framebuffer
> > > call silently fails.  fbcon is builtin to the kernel, so when drmfb
> > > exits, unregister_framebuffer will end up calling fbcon's
> > > fbcon_fb_unregistered() function via the notifier chain.  However,
> > > when fbcon_fb_unregistered calls unregister_con_driver(&fb_con) it
> > > ignores the return value, which is bad since unregister_con_driver
> > > left fbcon's routines active (due to fbcon still being bound to the
> > > console) even while unregister_framebuffer freed their underlying
> > > structures.
> >
> > Okay, we can do that. This was not done before because
> > unregister_framebuffer was only called on rmmod <module>.  But checking
> > for the return error and have it propagate to the driver should not be a
> > problem.
> >
> > I'll send a patch to you and to akpm soon.
> 
> Great!  Thanks.
> 
> > >   So when unregister_framebuffer returns, the
> > > very next console operation causes an oops or worse (I usually see
> > > hide_cursor->fbcon_cursor die when it tries to get at
> > > info->fbcon_par).
> > >
> > > However, it doesn't appear that there's a way for fb drivers to unbind
> > > themselves from the console at unload time, so we have to do it
> > > manually.
> >
> > You cannot unbind framebuffer drivers independently from the console
> > layer because the console is holding a reference count on them.
> >
> > FYI: this was what I did initially, but akpm objected :-).
> >
> > > Should there be a way to unbind it from driver code?  Maybe by
> > > exporting a wrapper to unbind_con_driver?
> >
> > Yes, you can expose unbind_con_driver(), I don't mind. You can do it
> > first in your tree, then when you need it for mainline, let me know.
> 
> So using unbind_con_driver is ok since we go through the console layer and 
> all the refcounting is kosher?

Yes.

>   The only other thing with 
> unbind_con_driver is I'm not sure about the other arguments (first, last, 
> & default) should be if called from a driver context.

No, they're only for the console.  So, if you're writing a pure fbdev
driver, then the user has to unbind the console from the VT layer
manually.  If you are writing an fbdev/console-combo driver, then you
can do that by calling unbind_con_driver() first before
unregister_framebuffer().

Tony


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