[PATCH] amdgpu: prevent NULL pointer dereference if ATIF is not supported

[Antonio Quartulli <antonio@mandelbit.com>]

acpi_evaluate_object() may return AE_NOT_FOUND (failure), which
would result in dereferencing buffer.pointer (obj) while being NULL.

Bail out also when status is AE_NOT_FOUND with a proper error message.

This fixes 1 FORWARD_NULL issue reported by Coverity
Report: CID 1600951:  Null pointer dereferences  (FORWARD_NULL)

Signed-off-by: Antonio Quartulli <antonio@mandelbit.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c
index cce85389427f..f10c3261a4ab 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c
@@ -172,10 +172,13 @@ static union acpi_object *amdgpu_atif_call(struct amdgpu_atif *atif,
 				      &buffer);
 	obj = (union acpi_object *)buffer.pointer;
 
-	/* Fail if calling the method fails and ATIF is supported */
-	if (ACPI_FAILURE(status) && status != AE_NOT_FOUND) {
-		DRM_DEBUG_DRIVER("failed to evaluate ATIF got %s\n",
-				 acpi_format_exception(status));
+	/* Fail if calling the method fails */
+	if (ACPI_FAILURE(status)) {
+		if (status != AE_NOT_FOUND)
+			DRM_DEBUG_DRIVER("failed to evaluate ATIF got %s\n",
+					 acpi_format_exception(status));
+		else
+			DRM_DEBUG_DRIVER("ATIF not supported\n");
 		kfree(obj);
 		return NULL;
 	}
-- 
2.45.2