drm/i915/gem: Differentiate oom failures from invalid map types

After a cursory check on the parameters to i915_gem_object_pin_map(),
where we return a precise error, if the backend rejects the mapping we
always return PTR_ERR(-ENOMEM). Let us also return a more precise error
here so we can differentiate between running out of memory and
programming errors (or situations where we may be trying different paths
and looking for an error from an unsupported map).
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201127195334.13134-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gem/i915_gem_pages.c

@@ -281,7 +281,7 @@ static void *i915_gem_object_map_page(struct drm_i915_gem_object *obj,
 		/* Too big for stack -- allocate temporary array instead */
 		pages = kvmalloc_array(n_pages, sizeof(*pages), GFP_KERNEL);
 		if (!pages)
-			return NULL;
+			return ERR_PTR(-ENOMEM);
 	}
 
 	i = 0;
@@ -305,13 +305,13 @@ static void *i915_gem_object_map_pfn(struct drm_i915_gem_object *obj,
 	void *vaddr;
 
 	if (type != I915_MAP_WC)
-		return NULL;
+		return ERR_PTR(-ENODEV);
 
 	if (n_pfn > ARRAY_SIZE(stack)) {
 		/* Too big for stack -- allocate temporary array instead */
 		pfns = kvmalloc_array(n_pfn, sizeof(*pfns), GFP_KERNEL);
 		if (!pfns)
-			return NULL;
+			return ERR_PTR(-ENOMEM);
 	}
 
 	i = 0;
@@ -349,8 +349,10 @@ void *i915_gem_object_pin_map(struct drm_i915_gem_object *obj,
 			GEM_BUG_ON(i915_gem_object_has_pinned_pages(obj));
 
 			err = ____i915_gem_object_get_pages(obj);
-			if (err)
-				goto err_unlock;
+			if (err) {
+				ptr = ERR_PTR(err);
+				goto out_unlock;
+			}
 
 			smp_mb__before_atomic();
 		}
@@ -362,7 +364,7 @@ void *i915_gem_object_pin_map(struct drm_i915_gem_object *obj,
 	ptr = page_unpack_bits(obj->mm.mapping, &has_type);
 	if (ptr && has_type != type) {
 		if (pinned) {
-			err = -EBUSY;
+			ptr = ERR_PTR(-EBUSY);
 			goto err_unpin;
 		}
 
@@ -374,15 +376,13 @@ void *i915_gem_object_pin_map(struct drm_i915_gem_object *obj,
 	if (!ptr) {
 		if (GEM_WARN_ON(type == I915_MAP_WC &&
 				!static_cpu_has(X86_FEATURE_PAT)))
-			ptr = NULL;
+			ptr = ERR_PTR(-ENODEV);
 		else if (i915_gem_object_has_struct_page(obj))
 			ptr = i915_gem_object_map_page(obj, type);
 		else
 			ptr = i915_gem_object_map_pfn(obj, type);
-		if (!ptr) {
-			err = -ENOMEM;
+		if (IS_ERR(ptr))
 			goto err_unpin;
-		}
 
 		obj->mm.mapping = page_pack_bits(ptr, type);
 	}
@@ -393,8 +393,6 @@ void *i915_gem_object_pin_map(struct drm_i915_gem_object *obj,
 
 err_unpin:
 	atomic_dec(&obj->mm.pages_pin_count);
-err_unlock:
-	ptr = ERR_PTR(err);
 	goto out_unlock;
 }