drm/i915: Kerneldoc for i915_gem_evict.c

Request by Ben Widawsky in his review of a patch touching this code.

v2: Clarify the disdinction between evicting vmas (to free up virtual
address space) and evicting objects (to free up actual system memory).
Suggested by Ben.

Cc: Ben Widawsky <benjamin.widawsky@intel.com>
Acked-by: Ben Widawsky <benjamin.widawsky@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem_evict.c

@@ -46,6 +46,25 @@ mark_free(struct i915_vma *vma, struct list_head *unwind)
 	return drm_mm_scan_add_block(&vma->node);
 }
 
+/**
+ * i915_gem_evict_something - Evict vmas to make room for binding a new one
+ * @dev: drm_device
+ * @vm: address space to evict from
+ * @size: size of the desired free space
+ * @alignment: alignment constraint of the desired free space
+ * @cache_level: cache_level for the desired space
+ * @mappable: whether the free space must be mappable
+ * @nonblocking: whether evicting active objects is allowed or not
+ *
+ * This function will try to evict vmas until a free space satisfying the
+ * requirements is found. Callers must check first whether any such hole exists
+ * already before calling this function.
+ *
+ * This function is used by the object/vma binding code.
+ *
+ * To clarify: This is for freeing up virtual address space, not for freeing
+ * memory in e.g. the shrinker.
+ */
 int
 i915_gem_evict_something(struct drm_device *dev, struct i915_address_space *vm,
 			 int min_size, unsigned alignment, unsigned cache_level,
@@ -177,19 +196,19 @@ found:
 }
 
 /**
- * i915_gem_evict_vm - Try to free up VM space
+ * i915_gem_evict_vm - Evict all idle vmas from a vm
  *
- * @vm: Address space to evict from
+ * @vm: Address space to cleanse
  * @do_idle: Boolean directing whether to idle first.
  *
- * VM eviction is about freeing up virtual address space. If one wants fine
- * grained eviction, they should see evict something for more details. In terms
- * of freeing up actual system memory, this function may not accomplish the
- * desired result. An object may be shared in multiple address space, and this
- * function will not assert those objects be freed.
+ * This function evicts all idles vmas from a vm. If all unpinned vmas should be
+ * evicted the @do_idle needs to be set to true.
  *
- * Using do_idle will result in a more complete eviction because it retires, and
- * inactivates current BOs.
+ * This is used by the execbuf code as a last-ditch effort to defragment the
+ * address space.
+ *
+ * To clarify: This is for freeing up virtual address space, not for freeing
+ * memory in e.g. the shrinker.
  */
 int i915_gem_evict_vm(struct i915_address_space *vm, bool do_idle)
 {
@@ -213,6 +232,14 @@ int i915_gem_evict_vm(struct i915_address_space *vm, bool do_idle)
 	return 0;
 }
 
+/**
+ * i915_gem_evict_everything - Try to evict all objects
+ * @dev: Device to evict objects for
+ *
+ * This functions tries to evict all gem objects from all address spaces. Used
+ * by the shrinker as a last-ditch effort and for suspend, before releasing the
+ * backing storage of all unbound objects.
+ */
 int
 i915_gem_evict_everything(struct drm_device *dev)
 {