[PATCH] drm: add debug logs for drm_mode_atomic_ioctl errors

[Simon Ser]

Be nice to user-space and log what happened when returning EINVAL in
drm_mode_atomic_ioctl.

Signed-off-by: Simon Ser <contact at emersion.fr>
Cc: Daniel Vetter <daniel at ffwll.ch>
Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
Cc: Maxime Ripard <mripard at kernel.org>
Cc: Thomas Zimmermann <tzimmermann at suse.de>
---
 drivers/gpu/drm/drm_atomic_uapi.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/drm_atomic_uapi.c b/drivers/gpu/drm/drm_atomic_uapi.c
index 25c269bc4681..68d767420082 100644
--- a/drivers/gpu/drm/drm_atomic_uapi.c
+++ b/drivers/gpu/drm/drm_atomic_uapi.c
@@ -1303,22 +1303,30 @@ int drm_mode_atomic_ioctl(struct drm_device *dev,
 	 * though this may be a bit overkill, since legacy userspace
 	 * wouldn't know how to call this ioctl)
 	 */
-	if (!file_priv->atomic)
+	if (!file_priv->atomic) {
+		DRM_DEBUG_ATOMIC("atomic commit failed: atomic cap not enabled\n");
 		return -EINVAL;
+	}
 
-	if (arg->flags & ~DRM_MODE_ATOMIC_FLAGS)
+	if (arg->flags & ~DRM_MODE_ATOMIC_FLAGS) {
+		DRM_DEBUG_ATOMIC("atomic commit failed: invalid flag\n");
 		return -EINVAL;
+	}
 
 	if (arg->reserved)
 		return -EINVAL;
 
-	if (arg->flags & DRM_MODE_PAGE_FLIP_ASYNC)
+	if (arg->flags & DRM_MODE_PAGE_FLIP_ASYNC) {
+		DRM_DEBUG_ATOMIC("atomic commit failed: invalid flag DRM_MODE_PAGE_FLIP_ASYNC\n");
 		return -EINVAL;
+	}
 
 	/* can't test and expect an event at the same time. */
 	if ((arg->flags & DRM_MODE_ATOMIC_TEST_ONLY) &&
-			(arg->flags & DRM_MODE_PAGE_FLIP_EVENT))
+			(arg->flags & DRM_MODE_PAGE_FLIP_EVENT)) {
+		DRM_DEBUG_ATOMIC("atomic commit failed: page-flip event requested with test-only commit\n");
 		return -EINVAL;
+	}
 
 	state = drm_atomic_state_alloc(dev);
 	if (!state)
-- 
2.29.2