x86: Fix iommu=soft boot option

iommu=soft boot option forces the kernel to use swiotlb.

( This has the side-effect of enabling the swiotlb over the
  GART if this boot option is provided. This is the desired
  behavior of the swiotlb boot option and works like that
  for all other hw-IOMMU drivers. )
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Cc: yinghai@kernel.org
LKML-Reference: <20091125084611O.fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/pci-swiotlb.c

@@ -50,6 +50,8 @@ static struct dma_map_ops swiotlb_dma_ops = {
  */
 int __init pci_swiotlb_init(void)
 {
+	int use_swiotlb = swiotlb | swiotlb_force;
+
 	/* don't initialize swiotlb if iommu=off (no_iommu=1) */
 #ifdef CONFIG_X86_64
 	if (!no_iommu && max_pfn > MAX_DMA32_PFN)
@@ -63,5 +65,5 @@ int __init pci_swiotlb_init(void)
 		dma_ops = &swiotlb_dma_ops;
 	}
 
-	return swiotlb_force;
+	return use_swiotlb;
 }