x86: add alloc_coherent dma_ops callback to GART driver

[ v2 - x86: make gart_alloc_coherent return zeroed memory

  FUJITA Tomonori pointed it out that the dma_alloc_coherent function
  should return memory set to zero. This patch adds this to the GART
  implementation too. ]

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/pci-gart_64.c

@@ -499,6 +499,26 @@ error:
 	return 0;
 }
 
+/* allocate and map a coherent mapping */
+static void *
+gart_alloc_coherent(struct device *dev, size_t size, dma_addr_t *dma_addr,
+		    gfp_t flag)
+{
+	void *vaddr;
+
+	vaddr = (void *)__get_free_pages(flag | __GFP_ZERO, get_order(size));
+	if (!vaddr)
+		return NULL;
+
+	*dma_addr = gart_map_single(dev, __pa(vaddr), size, DMA_BIDIRECTIONAL);
+	if (*dma_addr != bad_dma_address)
+		return vaddr;
+
+	free_pages((unsigned long)vaddr, get_order(size));
+
+	return NULL;
+}
+
 static int no_agp;
 
 static __init unsigned long check_iommu_size(unsigned long aper, u64 aper_size)
@@ -701,6 +721,7 @@ static struct dma_mapping_ops gart_dma_ops = {
 	.sync_sg_for_device		= NULL,
 	.map_sg				= gart_map_sg,
 	.unmap_sg			= gart_unmap_sg,
+	.alloc_coherent			= gart_alloc_coherent,
 };
 
 void gart_iommu_shutdown(void)