[PATCH] x86_64: Fix swiotlb=force

It was broken before. But having it is important as possible hardware
bug workaround.

And previously there was no way to force swiotlb if there is another IOMMU.
Side effect is that iommu=force won't force swiotlb anymore even if there
isn't another IOMMU.
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/x86_64/kernel/pci-swiotlb.c

@@ -31,8 +31,9 @@ struct dma_mapping_ops swiotlb_dma_ops = {
 void pci_swiotlb_init(void)
 {
 	/* don't initialize swiotlb if iommu=off (no_iommu=1) */
-	if (!iommu_detected && !no_iommu &&
-	    (end_pfn > MAX_DMA32_PFN || force_iommu))
+	if (!iommu_detected && !no_iommu && end_pfn > MAX_DMA32_PFN)
+	       swiotlb = 1;
+	if (swiotlb_force)
 		swiotlb = 1;
 	if (swiotlb) {
 		printk(KERN_INFO "PCI-DMA: Using software bounce buffering for IO (SWIOTLB)\n");

include/asm-x86_64/swiotlb.h

@@ -42,6 +42,8 @@ extern void swiotlb_free_coherent (struct device *hwdev, size_t size,
 extern int swiotlb_dma_supported(struct device *hwdev, u64 mask);
 extern void swiotlb_init(void);
 
+extern int swiotlb_force;
+
 #ifdef CONFIG_SWIOTLB
 extern int swiotlb;
 #else