[PATCH] x86_64: GART DMA merging fix

Don't touch the non DMA members in the sg list in dma_map_sg in the IOMMU

Some drivers (in particular ST) ran into problems because they reused the sg
lists after passing them to pci_map_sg().  The merging procedure in the K8
GART IOMMU corrupted the state.  This patch changes it to only touch the dma*
entries during merging, but not the other fields.  Approach suggested by Dave
Miller.
Signed-off-by: NAndi Kleen <ak@suse.de>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

arch/x86_64/kernel/pci-gart.c

@@ -310,7 +310,7 @@ void gart_unmap_sg(struct device *dev, struct scatterlist *sg, int nents, int di
 
 	for (i = 0; i < nents; i++) {
 		struct scatterlist *s = &sg[i];
-		if (!s->dma_length || !s->length)
+		if (!s->dma_length)
 			break;
 		dma_unmap_single(dev, s->dma_address, s->dma_length, dir);
 	}
@@ -364,7 +364,6 @@ static int __dma_map_cont(struct scatterlist *sg, int start, int stopat,
 		
 		BUG_ON(i > start && s->offset);
 		if (i == start) {
-			*sout = *s; 
 			sout->dma_address = iommu_bus_base;
 			sout->dma_address += iommu_page*PAGE_SIZE + s->offset;
 			sout->dma_length = s->length;
@@ -391,7 +390,6 @@ static inline int dma_map_cont(struct scatterlist *sg, int start, int stopat,
 {
 	if (!need) { 
 		BUG_ON(stopat - start != 1);
-		*sout = sg[start]; 
 		sout->dma_length = sg[start].length; 
 		return 0;
 	}