1 files changed, 29 insertions, 5 deletions

diff --git a/arch/x86/kernel/pci-dma_32.c b/arch/x86/kernel/pci-dma_32.c
index debe9119b724..11f100a5f034 100644
--- a/arch/x86/kernel/pci-dma_32.c
+++ b/arch/x86/kernel/pci-dma_32.c
@@ -76,6 +76,8 @@ void *dma_alloc_coherent(struct device *dev, size_t size,
         struct page *page;
         dma_addr_t bus;
         int order = get_order(size);
+        unsigned long dma_mask = 0;
+
         /* ignore region specifiers */
         gfp &= ~(__GFP_DMA | __GFP_HIGHMEM);
 
@@ -85,15 +87,37 @@ void *dma_alloc_coherent(struct device *dev, size_t size,
         if (!dev)
                 dev = &fallback_dev;
 
+        dma_mask = dev->coherent_dma_mask;
+        if (dma_mask == 0)
+                dma_mask = DMA_32BIT_MASK;
+
+ again:
         page = dma_alloc_pages(dev, gfp, order);
         if (page == NULL)
                 return NULL;
 
-        ret = page_address(page);
-        bus = page_to_phys(page);
-
-        memset(ret, 0, size);
-        *dma_handle = bus;
+        {
+                int high, mmu;
+                bus = page_to_phys(page);
+                ret = page_address(page);
+                high = (bus + size) >= dma_mask;
+                mmu = high;
+                if (force_iommu && !(gfp & GFP_DMA))
+                        mmu = 1;
+                else if (high) {
+                        free_pages((unsigned long)ret,
+                                   get_order(size));
+
+                        /* Don't use the 16MB ZONE_DMA unless absolutely
+                           needed. It's better to use remapping first. */
+                        if (dma_mask < DMA_32BIT_MASK && !(gfp & GFP_DMA)) {
+                                gfp = (gfp & ~GFP_DMA32) | GFP_DMA;
+                                goto again;
+                        }
+                }
+                memset(ret, 0, size);
+                *dma_handle = bus;
+        }
 
         return ret;
 }