drm/rockchip: use __GFP_DMA32 for shmem-backed gem

Rockchip requires bo-pages to be in the DMA32 zone. Explicitly request this
by setting __GFP_DMA32 as mapping-gfp-mask during shmem initialization.
This drops HIGHMEM from the gfp-mask and uses DMA32 instead. shmem-core
takes care to relocate pages during swap-in in case they have been loaded
into the wrong zone.

It is _not_ possible to pass __GFP_DMA32 to shmem_read_mapping_page_gfp()
as the page might have already been swapped-in at that time. The zone-mask
must be set during initialization and be kept constant for now.

Change-Id: I6db4f9e8ed716a1f7c90c7d92920122a484bf45d
Signed-off-by: Jianqun Xu <jay.xu@rock-chips.com>

Author: jayxurockchip

drivers/gpu/drm/rockchip/rockchip_drm_gem.c

@@ -592,11 +592,8 @@ rockchip_gem_alloc_object(struct drm_device *drm, unsigned int size)
 
 	drm_gem_object_init(drm, obj, size);
 
-	if (IS_ENABLED(CONFIG_ARM_LPAE)) {
-		mapping = file_inode(obj->filp)->i_mapping;
-		mapping_set_gfp_mask(mapping,
-				     mapping_gfp_mask(mapping) | __GFP_DMA32);
-	}
+	mapping = file_inode(obj->filp)->i_mapping;
+	mapping_set_gfp_mask(mapping, GFP_USER | __GFP_DMA32);
 
 	return rk_obj;
 }