[PATCH RFC] drm/atomic: Fall back to legacy call back in *_connector_dpms()

[Jyri Sarha]

Fall back to legacy drm_helper_connector_dpms() call back in
drm_atomic_helper_connector_dpms() if DRIVER_ATOMIC feature is not
present.

Calling drm_atomic_helper_connector_dpms() from non atomic driver
causes undefined behavior. This is a problem with componentized
encoder/connector drivers that may be bound to both atomic and
non atomic drivers.

Signed-off-by: Jyri Sarha <jsarha at ti.com>
---
This is just an alternative to this:
https://lists.freedesktop.org/archives/dri-devel/2016-January/098867.html

Either one of the patches should be taken for Beaglebone-black, or any
other non atomic driver using tda998x, to work.

 drivers/gpu/drm/drm_atomic_helper.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index 57cccd6..6ad0303 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -2344,6 +2344,9 @@ int drm_atomic_helper_connector_dpms(struct drm_connector *connector,
 	bool active = false;
 	int old_mode = connector->dpms;
 
+	if (!drm_core_check_feature(connector->dev, DRIVER_ATOMIC))
+		return drm_helper_connector_dpms(connector, mode);
+
 	if (mode != DRM_MODE_DPMS_ON)
 		mode = DRM_MODE_DPMS_OFF;
 
-- 
1.9.1