drm/i915: Refactor ttm ghost obj detection

Currently i915_ttm_to_gem() returns NULL for ttm ghost
object which makes it unclear when we should add a NULL
check for a caller of i915_ttm_to_gem() as ttm ghost
objects are expected behaviour for certain cases.

Create a separate function to detect ttm ghost object and
use that in places where we expect a ghost obj from ttm.
Signed-off-by: Nirmoy Das <nirmoy.das@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221014131427.21102-1-nirmoy.das@intel.com

drivers/gpu/drm/i915/gem/i915_gem_ttm.c

@@ -279,7 +279,7 @@ static struct ttm_tt *i915_ttm_tt_create(struct ttm_buffer_object *bo,
 	struct i915_ttm_tt *i915_tt;
 	int ret;
 
-	if (!obj)
+	if (i915_ttm_is_ghost_object(bo))
 		return NULL;
 
 	i915_tt = kzalloc(sizeof(*i915_tt), GFP_KERNEL);
@@ -362,7 +362,7 @@ static bool i915_ttm_eviction_valuable(struct ttm_buffer_object *bo,
 {
 	struct drm_i915_gem_object *obj = i915_ttm_to_gem(bo);
 
-	if (!obj)
+	if (i915_ttm_is_ghost_object(bo))
 		return false;
 
 	/*
@@ -511,7 +511,7 @@ static void i915_ttm_delete_mem_notify(struct ttm_buffer_object *bo)
 	struct drm_i915_gem_object *obj = i915_ttm_to_gem(bo);
 	intel_wakeref_t wakeref = 0;
 
-	if (bo->resource && likely(obj)) {
+	if (bo->resource && !i915_ttm_is_ghost_object(bo)) {
 		/* ttm_bo_release() already has dma_resv_lock */
 		if (i915_ttm_cpu_maps_iomem(bo->resource))
 			wakeref = intel_runtime_pm_get(&to_i915(obj->base.dev)->runtime_pm);
@@ -624,7 +624,7 @@ static void i915_ttm_swap_notify(struct ttm_buffer_object *bo)
 	struct drm_i915_gem_object *obj = i915_ttm_to_gem(bo);
 	int ret;
 
-	if (!obj)
+	if (i915_ttm_is_ghost_object(bo))
 		return;
 
 	ret = i915_ttm_move_notify(bo);
@@ -657,7 +657,7 @@ static int i915_ttm_io_mem_reserve(struct ttm_device *bdev, struct ttm_resource
 	struct drm_i915_gem_object *obj = i915_ttm_to_gem(mem->bo);
 	bool unknown_state;
 
-	if (!obj)
+	if (i915_ttm_is_ghost_object(mem->bo))
 		return -EINVAL;
 
 	if (!kref_get_unless_zero(&obj->base.refcount))
@@ -690,7 +690,7 @@ static unsigned long i915_ttm_io_mem_pfn(struct ttm_buffer_object *bo,
 	unsigned long base;
 	unsigned int ofs;
 
-	GEM_BUG_ON(!obj);
+	GEM_BUG_ON(i915_ttm_is_ghost_object(bo));
 	GEM_WARN_ON(bo->ttm);
 
 	base = obj->mm.region->iomap.base - obj->mm.region->region.start;
@@ -1035,13 +1035,12 @@ static vm_fault_t vm_fault_ttm(struct vm_fault *vmf)
 	struct vm_area_struct *area = vmf->vma;
 	struct ttm_buffer_object *bo = area->vm_private_data;
 	struct drm_device *dev = bo->base.dev;
-	struct drm_i915_gem_object *obj;
+	struct drm_i915_gem_object *obj = i915_ttm_to_gem(bo);
 	intel_wakeref_t wakeref = 0;
 	vm_fault_t ret;
 	int idx;
 
-	obj = i915_ttm_to_gem(bo);
-	if (!obj)
+	if (i915_ttm_is_ghost_object(bo))
 		return VM_FAULT_SIGBUS;
 
 	/* Sanity check that we allow writing into this object */
@@ -1140,7 +1139,7 @@ static void ttm_vm_open(struct vm_area_struct *vma)
 	struct drm_i915_gem_object *obj =
 		i915_ttm_to_gem(vma->vm_private_data);
 
-	GEM_BUG_ON(!obj);
+	GEM_BUG_ON(i915_ttm_is_ghost_object(vma->vm_private_data));
 	i915_gem_object_get(obj);
 }
 
@@ -1149,7 +1148,7 @@ static void ttm_vm_close(struct vm_area_struct *vma)
 	struct drm_i915_gem_object *obj =
 		i915_ttm_to_gem(vma->vm_private_data);
 
-	GEM_BUG_ON(!obj);
+	GEM_BUG_ON(i915_ttm_is_ghost_object(vma->vm_private_data));
 	i915_gem_object_put(obj);
 }
 

drivers/gpu/drm/i915/gem/i915_gem_ttm.h

@@ -27,19 +27,27 @@ i915_gem_to_ttm(struct drm_i915_gem_object *obj)
  */
 void i915_ttm_bo_destroy(struct ttm_buffer_object *bo);
 
+/**
+ * i915_ttm_is_ghost_object - Check if the ttm bo is a ghost object.
+ * @bo: Pointer to the ttm buffer object
+ *
+ * Return: True if the ttm bo is not a i915 object but a ghost ttm object,
+ * False otherwise.
+ */
+static inline bool i915_ttm_is_ghost_object(struct ttm_buffer_object *bo)
+{
+	return bo->destroy != i915_ttm_bo_destroy;
+}
+
 /**
  * i915_ttm_to_gem - Convert a struct ttm_buffer_object to an embedding
  * struct drm_i915_gem_object.
  *
- * Return: Pointer to the embedding struct ttm_buffer_object, or NULL
- * if the object was not an i915 ttm object.
+ * Return: Pointer to the embedding struct ttm_buffer_object.
  */
 static inline struct drm_i915_gem_object *
 i915_ttm_to_gem(struct ttm_buffer_object *bo)
 {
-	if (bo->destroy != i915_ttm_bo_destroy)
-		return NULL;
-
 	return container_of(bo, struct drm_i915_gem_object, __do_not_access);
 }
 

drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c

@@ -560,7 +560,7 @@ int i915_ttm_move(struct ttm_buffer_object *bo, bool evict,
 	bool clear;
 	int ret;
 
-	if (GEM_WARN_ON(!obj)) {
+	if (GEM_WARN_ON(i915_ttm_is_ghost_object(bo))) {
 		ttm_bo_move_null(bo, dst_mem);
 		return 0;
 	}