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

From: [email-masked] (Ville Syrjälä)
Date: Fri, 30 Sep 2016 23:42:19 +0300

On Fri, Sep 30, 2016 at 06:33:48PM +0200, Boris Brezillon wrote:
> On Fri, 30 Sep 2016 19:22:11 +0300
> Ville Syrj?l? <[email-masked]> wrote:
> 
> > 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.
> > > 
> > > Have you tried doing something like that?  
> > 
> > You shouldn't even be looking at the user provided coordinates. Also
> > you can't return an error from the atomic update hook. The void return
> > value should have been a decent hint ;)
> 
> Note that Maxime is not returning a value from the atomic update
> implementation (it's done in the atomic_check implem),

Ah, missed that. Anyway it's still the wrong thing to check since
negative coordinates are a perfectly valid thing to have.

> and I'm not
> checking crtc_x,y consistency at all (which is obviously wrong), I'm
> just blindly patching the values in sun4i_backend helpers.
> 
> > The right fix would be
> > to move all the error handling into the atomic check hook, which
> > probably should just call the helper to clip the coordinates and
> > whatnot. Then the update hook can just use at the clipped 
> > coordinates when programming the hw registers.
> 
> That's probably the best approach indeed, but that means having our
> private sun4i_plane_state struct where we would store the patched
> crtc_{w,h,x,y} info.

Nope. The src/dst rects are now stored in drm_plane_state. Assuming my
patches went in already. I think they did.

> 
> Anyway, before we do that, that's probably better to check if it really
> works on this HW (which is why I sent this informal patch).

Most hardware can't do negative coordinates natively. But when things
get clipped, the negative coordinates disappear. Then the only question
left is whether the resulting coordinates are fullscreen or not, and
whether the hardware can handle the "not" case.

> 
> > 
> > >   
> > > --->8---  
> > > diff --git a/drivers/gpu/drm/sun4i/sun4i_backend.c b/drivers/gpu/drm/sun4i/sun4i_backend.c
> > > index 3ab560450a82..6b68804f3035 100644
> > > --- a/drivers/gpu/drm/sun4i/sun4i_backend.c
> > > +++ b/drivers/gpu/drm/sun4i/sun4i_backend.c
> > > @@ -110,15 +110,30 @@ int sun4i_backend_update_layer_coord(struct sun4i_backend *backend,
> > >  {
> > >         struct drm_plane_state *state = plane->state;
> > >         struct drm_framebuffer *fb = state->fb;
> > > +       int crtc_w, crtc_h, crtc_x, crtc_y;
> > >  
> > >         DRM_DEBUG_DRIVER("Updating layer %d\n", layer);
> > >  
> > > +       crtc_x = state->crtc_x;
> > > +       crtc_y = state->crtc_y;
> > > +       crtc_w = state->crtc_w;
> > > +       crtc_h = state->crtc_h;
> > > +
> > > +       if (crtc_x < 0) {
> > > +               crtc_w += crtx_x;
> > > +               crtc_x = 0;
> > > +       }
> > > +
> > > +       if (crtc_y < 0) {
> > > +               crtc_h += crtx_y;
> > > +               crtc_y = 0;
> > > +       }
> > > +
> > >         if (plane->type == DRM_PLANE_TYPE_PRIMARY) {
> > >                 DRM_DEBUG_DRIVER("Primary layer, updating global size W: %u H: %u\n",
> > >                                  state->crtc_w, state->crtc_h);
> > >                 regmap_write(backend->regs, SUN4I_BACKEND_DISSIZE_REG,
> > > -                            SUN4I_BACKEND_DISSIZE(state->crtc_w,
> > > -                                                  state->crtc_h));
> > > +                            SUN4I_BACKEND_DISSIZE(crtc_w, crtc_h));
> > >         }
> > >  
> > >         /* Set the line width */
> > > @@ -130,15 +145,13 @@ int sun4i_backend_update_layer_coord(struct sun4i_backend *backend,
> > >         DRM_DEBUG_DRIVER("Layer size W: %u H: %u\n",
> > >                          state->crtc_w, state->crtc_h);
> > >         regmap_write(backend->regs, SUN4I_BACKEND_LAYSIZE_REG(layer),
> > > -                    SUN4I_BACKEND_LAYSIZE(state->crtc_w,
> > > -                                          state->crtc_h));
> > > +                    SUN4I_BACKEND_LAYSIZE(crtc_w, crtc_h));
> > >  
> > >         /* Set base coordinates */
> > >         DRM_DEBUG_DRIVER("Layer coordinates X: %d Y: %d\n",
> > >                          state->crtc_x, state->crtc_y);
> > >         regmap_write(backend->regs, SUN4I_BACKEND_LAYCOOR_REG(layer),
> > > -                    SUN4I_BACKEND_LAYCOOR(state->crtc_x,
> > > -                                          state->crtc_y));
> > > +                    SUN4I_BACKEND_LAYCOOR(crtc_x, crtc_y));
> > >  
> > >         return 0;
> > >  }
> > > @@ -198,6 +211,12 @@ int sun4i_backend_update_layer_buffer(struct sun4i_backend *backend,
> > >         paddr += (state->src_x >> 16) * bpp;
> > >         paddr += (state->src_y >> 16) * fb->pitches[0];
> > >  
> > > +       if (state->crtc_x < 0)
> > > +               paddr -= bpp * state->crtc_x;
> > > +
> > > +       if (state->crtc_y < 0)
> > > +               paddr -= fb->pitches[0] * state->crtc_y;
> > > +
> > >         DRM_DEBUG_DRIVER("Setting buffer address to %pad\n", &paddr);
> > >  
> > >         /* Write the 32 lower bits of the address (in bits) */
> > > _______________________________________________
> > > dri-devel mailing list
> > > dri-devel at lists.freedesktop.org
> > > https://lists.freedesktop.org/mailman/listinfo/dri-devel  
> > 

-- 
Ville Syrj?l?
Intel OTC