radeon: Disable both CRTCs during mode switch

Reconfiguring one CRTC whilst the other is running can cause a hang under
some circumstances. Unfortunately we haven't pinpointed exactly what those
circumstances are, so disable both CRTCs for every mode switch.

Signed-off-by: Pierre Ossman <pierre@ossman.eu>
---

diff --git a/drivers/gpu/drm/radeon/radeon_legacy_crtc.c b/drivers/gpu/drm/radeon/radeon_legacy_crtc.c
index 8d0b7aa..6a7b82f 100644
--- a/drivers/gpu/drm/radeon/radeon_legacy_crtc.c
+++ b/drivers/gpu/drm/radeon/radeon_legacy_crtc.c
 -1042,12 +1052,29 @@ static int radeon_crtc_mode_set(struct drm_crtc *crtc,
 
 static void radeon_crtc_prepare(struct drm_crtc *crtc)
 {
-       radeon_crtc_dpms(crtc, DRM_MODE_DPMS_OFF);
+       struct drm_device *dev = crtc->dev;
+       struct radeon_device *rdev = dev->dev_private;
+
+       /*
+        * The hardware wedges sometimes if you reconfigure one CRTC
+        * whilst the other is running (see fdo bug #24611).
+        */
+       radeon_crtc_dpms(&rdev->mode_info.crtcs[0]->base, DRM_MODE_DPMS_OFF);
+       radeon_crtc_dpms(&rdev->mode_info.crtcs[1]->base, DRM_MODE_DPMS_OFF);
 }
 
 static void radeon_crtc_commit(struct drm_crtc *crtc)
 {
-       radeon_crtc_dpms(crtc, DRM_MODE_DPMS_ON);
+       struct drm_device *dev = crtc->dev;
+       struct radeon_device *rdev = dev->dev_private;
+
+       /*
+        * Reenable the CRTCs that should be running.
+        */
+       if (rdev->mode_info.crtcs[0]->base.enabled)
+               radeon_crtc_dpms(&rdev->mode_info.crtcs[0]->base, DRM_MODE_DPMS_ON);
+       if (rdev->mode_info.crtcs[1]->base.enabled)
+               radeon_crtc_dpms(&rdev->mode_info.crtcs[1]->base, DRM_MODE_DPMS_ON);
 }
 
 static const struct drm_crtc_helper_funcs legacy_helper_funcs = {