[PATCH v2 4/5] drm/vmwgfx: Fix crtc's atomic check conditional

[Zack Rusin <zack.rusin@broadcom.com>]

The conditional was supposed to prevent enabling of a crtc state
without a set primary plane. Accidently it also prevented disabling
crtc state with a set primary plane. Neither is correct.

Fix the conditional and just driver-warn when a crtc state has been
enabled without a primary plane which will help debug broken userspace.

Fixes IGT's kms_atomic_interruptible and kms_atomic_transition tests.

Signed-off-by: Zack Rusin <zack.rusin@broadcom.com>
Fixes: 06ec41909e31 ("drm/vmwgfx: Add and connect CRTC helper functions")
Cc: Broadcom internal kernel review list <bcm-kernel-feedback-list@broadcom.com>
Cc: dri-devel@lists.freedesktop.org
Cc: <stable@vger.kernel.org> # v4.12+
Reviewed-by: Ian Forbes <ian.forbes@broadcom.com>
Reviewed-by: Martin Krastev <martin.krastev@broadcom.com>
---
 drivers/gpu/drm/vmwgfx/vmwgfx_kms.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c b/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c
index e33e5993d8fc..13b2820cae51 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c
@@ -931,6 +931,7 @@ int vmw_du_cursor_plane_atomic_check(struct drm_plane *plane,
 int vmw_du_crtc_atomic_check(struct drm_crtc *crtc,
 			     struct drm_atomic_state *state)
 {
+	struct vmw_private *vmw = vmw_priv(crtc->dev);
 	struct drm_crtc_state *new_state = drm_atomic_get_new_crtc_state(state,
 									 crtc);
 	struct vmw_display_unit *du = vmw_crtc_to_du(new_state->crtc);
@@ -938,9 +939,13 @@ int vmw_du_crtc_atomic_check(struct drm_crtc *crtc,
 	bool has_primary = new_state->plane_mask &
 			   drm_plane_mask(crtc->primary);
 
-	/* We always want to have an active plane with an active CRTC */
-	if (has_primary != new_state->enable)
-		return -EINVAL;
+	/*
+	 * This is fine in general, but broken userspace might expect
+	 * some actual rendering so give a clue as why it's blank.
+	 */
+	if (new_state->enable && !has_primary)
+		drm_dbg_driver(&vmw->drm,
+			       "CRTC without a primary plane will be blank.\n");
 
 
 	if (new_state->connector_mask != connector_mask &&
-- 
2.40.1