[PATCH] HACK: drm: Allow encoders to be reenabled

[Thierry Reding]

When running the xf86-video-modesetting driver on top of a KMS driver,
leaving X causes the active encoder's DPMS mode to be set to off by the
drm_crtc_helper_disable() function. This doesn't set the connector's
DPMS mode to off, however, which results in subsequent calls to the
drm_helper_connector_dpms() function to not enable the encoder because
the connector's DPMS mode hasn't changed.

This patch works around this by forcing the connector's DPMS mode to off
if the encoder has changed, which always happens when a new mode is set
after drm_crtc_helper_disable(). The code that sets the connector DPMS
mode to on will then also enable the CRTC and encoder because the mode
actually changed.

Signed-off-by: Thierry Reding <thierry.reding at avionic-design.de>
---
 drivers/gpu/drm/drm_crtc_helper.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/drm_crtc_helper.c b/drivers/gpu/drm/drm_crtc_helper.c
index 1227adf..1b5ebf1 100644
--- a/drivers/gpu/drm/drm_crtc_helper.c
+++ b/drivers/gpu/drm/drm_crtc_helper.c
@@ -649,6 +649,12 @@ int drm_crtc_helper_set_config(struct drm_mode_set *set)
 			 */
 			if (connector->encoder)
 				connector->encoder->crtc = NULL;
+			/*
+			 * HACK: Force DPMS mode to off so that the encoder
+			 * has a chance of being reenabled along with the
+			 * connector later on.
+			 */
+			connector->dpms = DRM_MODE_DPMS_OFF;
 			connector->encoder = new_encoder;
 		}
 	}
-- 
1.8.0