drm/ttm: cleanup io_mem interface with nouveau

Nouveau is the only user of this functionality and evicting io space
on -EAGAIN is really a misuse of the return code.

Instead switch to using -ENOSPC here which makes much more sense and
simplifies the code.

This could unbreak something as we now cleanly return EAGAIN, but the
chance for this are rather low.
Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/378237/

drivers/gpu/drm/nouveau/nouveau_bo.c

@@ -1505,8 +1505,6 @@ nouveau_ttm_io_mem_reserve(struct ttm_bo_device *bdev, struct ttm_mem_reg *reg)
 			if (ret != 1) {
 				if (WARN_ON(ret == 0))
 					return -EINVAL;
-				if (ret == -ENOSPC)
-					return -EAGAIN;
 				return ret;
 			}
 

drivers/gpu/drm/ttm/ttm_bo_util.c

@@ -116,7 +116,7 @@ static int ttm_mem_io_evict(struct ttm_mem_type_manager *man)
 	struct ttm_buffer_object *bo;
 
 	if (!man->use_io_reserve_lru || list_empty(&man->io_reserve_lru))
-		return -EAGAIN;
+		return -ENOSPC;
 
 	bo = list_first_entry(&man->io_reserve_lru,
 			      struct ttm_buffer_object,
@@ -143,7 +143,7 @@ int ttm_mem_io_reserve(struct ttm_bo_device *bdev,
 	    mem->bus.io_reserved_count++ == 0) {
 retry:
 		ret = bdev->driver->io_mem_reserve(bdev, mem);
-		if (ret == -EAGAIN) {
+		if (ret == -ENOSPC) {
 			ret = ttm_mem_io_evict(man);
 			if (ret == 0)
 				goto retry;