Subject: [PATCH] drm/sun4i: Check that the plane coordinates are not negative

From: [email-masked] (Boris Brezillon)
Date: Mon, 3 Oct 2016 18:18:40 +0200

On Mon, 3 Oct 2016 14:58:11 +0200
Maxime Ripard <[email-masked]> wrote:

> Hi Boris,
> 
> On Fri, Sep 30, 2016 at 06:08:26PM +0200, Boris Brezillon wrote:
> > On Fri, 30 Sep 2016 16:33:20 +0200
> > Maxime Ripard <[email-masked]> wrote:
> >   
> > > Our planes cannot be set at negative coordinates. Make sure we reject such
> > > configuration.
> > > 
> > > Reported-by: Boris Brezillon <[email-masked]>
> > > Signed-off-by: Maxime Ripard <[email-masked]>
> > > ---
> > >  drivers/gpu/drm/sun4i/sun4i_layer.c | 3 +++
> > >  1 file changed, 3 insertions(+)
> > > 
> > > diff --git a/drivers/gpu/drm/sun4i/sun4i_layer.c b/drivers/gpu/drm/sun4i/sun4i_layer.c
> > > index f0035bf5efea..f5463c4c2cde 100644
> > > --- a/drivers/gpu/drm/sun4i/sun4i_layer.c
> > > +++ b/drivers/gpu/drm/sun4i/sun4i_layer.c
> > > @@ -29,6 +29,9 @@ struct sun4i_plane_desc {
> > >  static int sun4i_backend_layer_atomic_check(struct drm_plane *plane,
> > >  					    struct drm_plane_state *state)
> > >  {
> > > +	if ((state->crtc_x < 0) || (state->crtc_y < 0))
> > > +		return -EINVAL;
> > > +  
> > 
> > Hm, I think it's a perfectly valid use case from the DRM framework and
> > DRM user PoV: you may want to place your plane at a negative CRTC
> > offset (which means part of the plane will be hidden).
> > 
> > Maybe I'm wrong, but it seems you can support that by adapting the
> > start address of your framebuffer pointer and the layer size.  
> 
> Indeed, that would probably work. This is even somewhat what we've
> been using to implement the VGA hack we use on the CHIP.
> 
> Can you send that patch?

Actually, Ville suggested a slightly different approach: use the
->src and ->dst in drm_plane_state.