drm: Kill ctx_count from struct drm_device

The only user of ctx_count is the via driver, and we can replace that
use with list_is_singular().

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_context.c

@@ -334,7 +334,6 @@ int drm_addctx(struct drm_device *dev, void *data,
 
 	mutex_lock(&dev->ctxlist_mutex);
 	list_add(&ctx_entry->head, &dev->ctxlist);
-	++dev->ctx_count;
 	mutex_unlock(&dev->ctxlist_mutex);
 
 	return 0;
@@ -432,7 +431,6 @@ int drm_rmctx(struct drm_device *dev, void *data,
 			if (pos->handle == ctx->handle) {
 				list_del(&pos->head);
 				kfree(pos);
-				--dev->ctx_count;
 			}
 		}
 	}

drivers/gpu/drm/drm_fops.c

@@ -524,7 +524,6 @@ int drm_release(struct inode *inode, struct file *filp)
 
 				list_del(&pos->head);
 				kfree(pos);
-				--dev->ctx_count;
 			}
 		}
 	}

drivers/gpu/drm/via/via_mm.c

@@ -79,7 +79,7 @@ int via_final_context(struct drm_device *dev, int context)
 
 	/* Linux specific until context tracking code gets ported to BSD */
 	/* Last context, perform cleanup */
-	if (dev->ctx_count == 1 && dev->dev_private) {
+	if (list_is_singular(&dev->ctxlist) && dev->dev_private) {
 		DRM_DEBUG("Last Context\n");
 		drm_irq_uninstall(dev);
 		via_cleanup_futex(dev_priv);

include/drm/drmP.h

@@ -1132,7 +1132,6 @@ struct drm_device {
 	/** \name Context handle management */
 	/*@{ */
 	struct list_head ctxlist;	/**< Linked list of context handles */
-	int ctx_count;			/**< Number of context handles */
 	struct mutex ctxlist_mutex;	/**< For ctxlist */
 
 	struct idr ctx_idr;