[PATCH] drm/atomic: refuse changing CRTC for planes directly

[Daniel Vetter]

Very strictly speaking this is possible if you have special hw and
genlocked CRTCs. In general switching a plane between two active CRTC
just won't work so well and is probably not tested at all. Just forbid
it.

I've put this into the core since I really couldn't come up with a
case where we don't want to enforce that. But if that ever happens it
would be easy to move this check into helpers.

v2: don't bother with complexity and just outright disallow plane
switching without the intermediate OFF state. Simplifies drivers, we
don't have any hw that could do it anyway and current atomic userspace
(weston) works like this already anyway.

Cc: Thierry Reding <thierry.reding at gmail.com>
Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
Cc: Daniel Stone <daniels at collabora.com>
Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
---
 drivers/gpu/drm/drm_atomic.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
index 434915448ea0..f27aae3fa765 100644
--- a/drivers/gpu/drm/drm_atomic.c
+++ b/drivers/gpu/drm/drm_atomic.c
@@ -663,6 +663,22 @@ drm_atomic_plane_get_property(struct drm_plane *plane,
 	return 0;
 }
 
+static bool
+plane_switching(struct drm_atomic_state *state,
+		struct drm_plane *plane,
+		struct drm_plane_state *plane_state)
+{
+	struct drm_crtc_state *crtc_state, *curr_crtc_state;
+
+	if (!plane->state->crtc || !plane_state->crtc)
+		return false;
+
+	if (plane->state->crtc == plane_state->crtc)
+		return false;
+
+	return true;
+}
+
 /**
  * drm_atomic_plane_check - check plane state
  * @plane: plane to check
@@ -734,6 +750,12 @@ static int drm_atomic_plane_check(struct drm_plane *plane,
 		return -ENOSPC;
 	}
 
+	if (plane_switching(state->state, plane, state)) {
+		DRM_DEBUG_ATOMIC("[PLANE:%d] switching CRTC directly\n",
+				 plane->base.id);
+		return -EINVAL;
+	}
+
 	return 0;
 }
 
-- 
2.5.0