drm/i915/gtt: Control cache domain of dma_map_page() directly

We already maually control the CPU cache for our page table directories,
so we can tell the dma mapper to skip doing it as well.
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/20180706122611.4142-2-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_gem_gtt.c

@@ -564,6 +564,7 @@ static int __setup_page_dma(struct i915_address_space *vm,
 	p->daddr = dma_map_page_attrs(vm->dma,
 				      p->page, 0, PAGE_SIZE,
 				      PCI_DMA_BIDIRECTIONAL,
+				      DMA_ATTR_SKIP_CPU_SYNC |
 				      DMA_ATTR_NO_WARN);
 	if (unlikely(dma_mapping_error(vm->dma, p->daddr))) {
 		vm_free_page(vm, p->page);
@@ -648,6 +649,7 @@ setup_scratch_page(struct i915_address_space *vm, gfp_t gfp)
 		addr = dma_map_page_attrs(vm->dma,
 					  page, 0, size,
 					  PCI_DMA_BIDIRECTIONAL,
+					  DMA_ATTR_SKIP_CPU_SYNC |
 					  DMA_ATTR_NO_WARN);
 		if (unlikely(dma_mapping_error(vm->dma, addr)))
 			goto free_page;