drm/i915: add dev_priv->mm.stolen_lock

Which should protect dev_priv->mm.stolen usage. This will allow us to
simplify the relationship between stolen memory, FBC and struct_mutex.

v2:
  - Rebase after the stolen_remove_node() dev_priv patch move.
  - I realized that after we fixed a few things related to the FBC CFB
    size checks, we're not reallocating the CFB anymore with FBC
    enabled, so we can just move all the locking to i915_gem_stolen.c
    and stop worrying about freezing all the stolen alocations while
    freeing/rellocating the CFB. This allows us to fix the "Too
    coarse" observation from Chris.
Suggested-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.h

@@ -1245,6 +1245,10 @@ struct intel_l3_parity {
 struct i915_gem_mm {
 	/** Memory allocator for GTT stolen memory */
 	struct drm_mm stolen;
+	/** Protects the usage of the GTT stolen memory allocator. This is
+	 * always the inner lock when overlapping with struct_mutex. */
+	struct mutex stolen_lock;
+
 	/** List of all objects in gtt_space. Used to restore gtt
 	 * mappings on resume */
 	struct list_head bound_list;

drivers/gpu/drm/i915/i915_gem_stolen.c

@@ -46,17 +46,25 @@ int i915_gem_stolen_insert_node(struct drm_i915_private *dev_priv,
 				struct drm_mm_node *node, u64 size,
 				unsigned alignment)
 {
+	int ret;
+
 	if (!drm_mm_initialized(&dev_priv->mm.stolen))
 		return -ENODEV;
 
-	return drm_mm_insert_node(&dev_priv->mm.stolen, node, size, alignment,
+	mutex_lock(&dev_priv->mm.stolen_lock);
+	ret = drm_mm_insert_node(&dev_priv->mm.stolen, node, size, alignment,
 				 DRM_MM_SEARCH_DEFAULT);
+	mutex_unlock(&dev_priv->mm.stolen_lock);
+
+	return ret;
 }
 
 void i915_gem_stolen_remove_node(struct drm_i915_private *dev_priv,
 				 struct drm_mm_node *node)
 {
+	mutex_lock(&dev_priv->mm.stolen_lock);
 	drm_mm_remove_node(node);
+	mutex_unlock(&dev_priv->mm.stolen_lock);
 }
 
 static unsigned long i915_stolen_to_physical(struct drm_device *dev)
@@ -184,6 +192,8 @@ int i915_gem_init_stolen(struct drm_device *dev)
 	u32 tmp;
 	int bios_reserved = 0;
 
+	mutex_init(&dev_priv->mm.stolen_lock);
+
 #ifdef CONFIG_INTEL_IOMMU
 	if (intel_iommu_gfx_mapped && INTEL_INFO(dev)->gen < 8) {
 		DRM_INFO("DMAR active, disabling use of stolen memory\n");
@@ -384,7 +394,9 @@ i915_gem_object_create_stolen_for_preallocated(struct drm_device *dev,
 
 	stolen->start = stolen_offset;
 	stolen->size = size;
+	mutex_lock(&dev_priv->mm.stolen_lock);
 	ret = drm_mm_reserve_node(&dev_priv->mm.stolen, stolen);
+	mutex_unlock(&dev_priv->mm.stolen_lock);
 	if (ret) {
 		DRM_DEBUG_KMS("failed to allocate stolen space\n");
 		kfree(stolen);