drm/atomic-helper: Reject legacy flips on a disabled pipe

We want this for consistency with existing page_flip semantics.

Since this spurred quite a discussion on IRC also document why we
reject event generation when the pipe is off: It's not that it's hard
to implement, but userspace has a track recording which proves that it's
way too easy to accidentally abuse and cause havoc. We want to make
sure userspace doesn't get away with that.

v2: Somehow thought we do reject events already, but that code only
existed in my imagination ... Also suggestions from Thierry.

Cc: Daniel Stone <daniels@collabora.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Thierry Reding <thierry.reding@gmail.com>
Reviewed-by: Daniel Stone <daniels@collabora.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1449564561-3896-4-git-send-email-daniel.vetter@ffwll.ch

1 files changed, 9 insertions, 0 deletions

diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index 26d258d0618b..738104b68d26 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -2284,6 +2284,15 @@ retry:
 		goto fail;
 	drm_atomic_set_fb_for_plane(plane_state, fb);
 
+	/* Make sure we don't accidentally do a full modeset. */
+	state->allow_modeset = false;
+	if (!crtc_state->active) {
+		DRM_DEBUG_ATOMIC("[CRTC:%d] disabled, rejecting legacy flip\n",
+				 crtc->base.id);
+		ret = -EINVAL;
+		goto fail;
+	}
+
 	ret = drm_atomic_async_commit(state);
 	if (ret != 0)
 		goto fail;