[PATCH 1/3] drm/atomic: Take the atomic toys away from X

[Daniel Vetter]

The -modesetting ddx has a totally broken idea of how atomic works:
- doesn't disable old connectors, assuming they get auto-disable like
  with the legacy setcrtc
- assumes ASYNC_FLIP is wired through for the atomic ioctl
- not a single call to TEST_ONLY

Iow the implementation is a 1:1 translation of legacy ioctls to
atomic, which is a) broken b) pointless.

We already have bugs in both i915 and amdgpu-DC where this prevents us
from enabling neat features.

If anyone ever cares about atomic in X we can easily add a new atomic
level (req->value == 2) for X to get back the shiny toys.

Since these broken versions of -modesetting have been shipping,
there's really no other way to get out of this bind.

References: https://gitlab.freedesktop.org/xorg/xserver/issues/629
References: https://gitlab.freedesktop.org/xorg/xserver/merge_requests/180
Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
Cc: Michel Dänzer <michel at daenzer.net>
Cc: Alex Deucher <alexdeucher at gmail.com>
Cc: Adam Jackson <ajax at redhat.com>
Cc: Sean Paul <sean at poorly.run>
Cc: David Airlie <airlied at linux.ie>
Cc: stable at vger.kernel.org
Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
---
 drivers/gpu/drm/drm_ioctl.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
index 2c120c58f72d..1cb7b4c3c87c 100644
--- a/drivers/gpu/drm/drm_ioctl.c
+++ b/drivers/gpu/drm/drm_ioctl.c
@@ -334,6 +334,9 @@ drm_setclientcap(struct drm_device *dev, void *data, struct drm_file *file_priv)
 		file_priv->universal_planes = req->value;
 		break;
 	case DRM_CLIENT_CAP_ATOMIC:
+		/* The modesetting DDX has a totally broken idea of atomic. */
+		if (strstr(current->comm, "X"))
+			return -EOPNOTSUPP;
 		if (!drm_core_check_feature(dev, DRIVER_ATOMIC))
 			return -EOPNOTSUPP;
 		if (req->value > 1)
-- 
2.23.0