drm/crtc-helper: fix locking for drm_helper_disable_unused_functions

We have two calling contexts for thise function:

- In the crtc helper code itself as part of the ->set_config
  implementation. In this calling context all modeset locks are
  already held, as they should.

- In drivers not implementing fastboot before the fbdev/fbcon setup
  and initialization. This has been added for all drivers in

  commit 76a39dbfb2d1bc45219839e5a95d4ceaf6ca114f
  Author: Daniel Vetter <daniel.vetter@ffwll.ch>
  Date:   Sun Jan 20 23:12:54 2013 +0100

      drm/fb-helper: don't disable everything in initial_config

  In this calling context we do not hold any modeset locks since the
  immediately following call to initialize the fbev emulation grabs
  all these locks themselves.

- There are two exceptions to the above rule: shmob doesn't have fbdev
  emulation support. I've manually checked the callchain up to the
  driver load function and no kms locks are held.

The right fix therefore is to split this helper into an internal and
external version and add the required locking to the function exported
to drivers.

This remedies locking inconsistencies exposed by me adding locking
WARNs as part of the recent kerneldoc abi polishing done in

commit 62ff94a5492175759546f8bc61383189d6b49122
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Thu Jan 23 22:18:47 2014 +0100

    drm/crtc-helper: remove LOCKING from kerneldoc

and

commit 63951385052f7974155fa38f962f0f4e9847f90a
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Thu Jan 23 15:14:15 2014 +0100

    drm/doc: Repleace LOCKING kerneldoc sections in drm_modes.c

v2: It helps when I actually git add the entire thing.

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Tested-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_crtc_helper.c

@@ -278,17 +278,7 @@ drm_encoder_disable(struct drm_encoder *encoder)
 		encoder->bridge->funcs->post_disable(encoder->bridge);
 }
 
-/**
- * drm_helper_disable_unused_functions - disable unused objects
- * @dev: DRM device
- *
- * This function walks through the entire mode setting configuration of @dev. It
- * will remove any crtc links of unused encoders and encoder links of
- * disconnected connectors. Then it will disable all unused encoders and crtcs
- * either by calling their disable callback if available or by calling their
- * dpms callback with DRM_MODE_DPMS_OFF.
- */
-void drm_helper_disable_unused_functions(struct drm_device *dev)
+static void __drm_helper_disable_unused_functions(struct drm_device *dev)
 {
 	struct drm_encoder *encoder;
 	struct drm_connector *connector;
@@ -323,6 +313,23 @@ void drm_helper_disable_unused_functions(struct drm_device *dev)
 		}
 	}
 }
+
+/**
+ * drm_helper_disable_unused_functions - disable unused objects
+ * @dev: DRM device
+ *
+ * This function walks through the entire mode setting configuration of @dev. It
+ * will remove any crtc links of unused encoders and encoder links of
+ * disconnected connectors. Then it will disable all unused encoders and crtcs
+ * either by calling their disable callback if available or by calling their
+ * dpms callback with DRM_MODE_DPMS_OFF.
+ */
+void drm_helper_disable_unused_functions(struct drm_device *dev)
+{
+	drm_modeset_lock_all(dev);
+	__drm_helper_disable_unused_functions(dev);
+	drm_modeset_unlock_all(dev);
+}
 EXPORT_SYMBOL(drm_helper_disable_unused_functions);
 
 /*
@@ -552,7 +559,7 @@ drm_crtc_helper_disable(struct drm_crtc *crtc)
 		}
 	}
 
-	drm_helper_disable_unused_functions(dev);
+	__drm_helper_disable_unused_functions(dev);
 	return 0;
 }
 
@@ -776,7 +783,7 @@ int drm_crtc_helper_set_config(struct drm_mode_set *set)
 				set->connectors[i]->funcs->dpms(set->connectors[i], DRM_MODE_DPMS_ON);
 			}
 		}
-		drm_helper_disable_unused_functions(dev);
+		__drm_helper_disable_unused_functions(dev);
 	} else if (fb_changed) {
 		set->crtc->x = set->x;
 		set->crtc->y = set->y;
@@ -1009,7 +1016,7 @@ void drm_helper_resume_force_mode(struct drm_device *dev)
 	}
 
 	/* disable the unused connectors while restoring the modesetting */
-	drm_helper_disable_unused_functions(dev);
+	__drm_helper_disable_unused_functions(dev);
 }
 EXPORT_SYMBOL(drm_helper_resume_force_mode);