radeon: Disable both CRTCs during mode switch

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

Signed-off-by: Pierre Ossman <pierre@ossman.eu>
Acked-by: Alex Deucher <alexdeucher@gmail.com>
---

diff --git a/drivers/gpu/drm/radeon/radeon_legacy_crtc.c b/drivers/gpu/drm/radeon/radeon_legacy_crtc.c
index 8d0b7aa..4ece480 100644
--- a/drivers/gpu/drm/radeon/radeon_legacy_crtc.c
+++ b/drivers/gpu/drm/radeon/radeon_legacy_crtc.c
@@ -1042,12 +1042,29 @@ 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 drm_crtc *crtci;
+
+       /*
+        * The hardware wedges sometimes if you reconfigure one CRTC
+        * whilst another is running (see fdo bug #24611).
+        */
+       list_for_each_entry(crtci, &dev->mode_config.crtc_list, head)
+               radeon_crtc_dpms(crtci, 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 drm_crtc *crtci;
+
+       /*
+        * Reenable the CRTCs that should be running.
+        */
+       list_for_each_entry(crtci, &dev->mode_config.crtc_list, head) {
+               if (crtci->enabled)
+                       radeon_crtc_dpms(crtci, DRM_MODE_DPMS_ON);
+       }
 }
 
 static const struct drm_crtc_helper_funcs legacy_helper_funcs = {