Revert "dma-mapping: reject __GFP_COMP in dma_alloc_attrs"

JIRA: https://issues.redhat.com/browse/RHEL-2542
Upstream Status: RHEL Only

This reverts commit a2cfbf0.

bnx2i/cnic currently fails to properly mmap its dma_alloc_coherent
buffers through a uio interface without being able to allocate compound
pages.  Revert this until we can get a better cnic fix.

Signed-off-by: Chris Leech <cleech@redhat.com>

Author: cleech

arch/arm/mm/dma-mapping.c

@@ -695,6 +695,14 @@ static void *__dma_alloc(struct device *dev, size_t size, dma_addr_t *handle,
 	if (mask < 0xffffffffULL)
 		gfp |= GFP_DMA;
 
+	/*
+	 * Following is a work-around (a.k.a. hack) to prevent pages
+	 * with __GFP_COMP being passed to split_page() which cannot
+	 * handle them.  The real problem is that this flag probably
+	 * should be 0 on ARM as it is not supported on this
+	 * platform; see CONFIG_HUGETLBFS.
+	 */
+	gfp &= ~(__GFP_COMP);
 	args.gfp = gfp;
 
 	*handle = DMA_MAPPING_ERROR;
@@ -1427,6 +1435,15 @@ static void *__arm_iommu_alloc_attrs(struct device *dev, size_t size,
 		return __iommu_alloc_simple(dev, size, gfp, handle,
 					    coherent_flag, attrs);
 
+	/*
+	 * Following is a work-around (a.k.a. hack) to prevent pages
+	 * with __GFP_COMP being passed to split_page() which cannot
+	 * handle them.  The real problem is that this flag probably
+	 * should be 0 on ARM as it is not supported on this
+	 * platform; see CONFIG_HUGETLBFS.
+	 */
+	gfp &= ~(__GFP_COMP);
+
 	pages = __iommu_alloc_buffer(dev, size, gfp, attrs, coherent_flag);
 	if (!pages)
 		return NULL;

drivers/iommu/dma-iommu.c

@@ -747,6 +747,9 @@ static struct page **__iommu_dma_alloc_pages(struct device *dev,
 	/* IOMMU can map any pages, so himem can also be used here */
 	gfp |= __GFP_NOWARN | __GFP_HIGHMEM;
 
+	/* It makes no sense to muck about with huge pages */
+	gfp &= ~__GFP_COMP;
+
 	while (count) {
 		struct page *page = NULL;
 		unsigned int order_size;

kernel/dma/mapping.c

@@ -494,14 +494,6 @@ void *dma_alloc_attrs(struct device *dev, size_t size, dma_addr_t *dma_handle,
 
 	WARN_ON_ONCE(!dev->coherent_dma_mask);
 
-	/*
-	 * DMA allocations can never be turned back into a page pointer, so
-	 * requesting compound pages doesn't make sense (and can't even be
-	 * supported at all by various backends).
-	 */
-	if (WARN_ON_ONCE(flag & __GFP_COMP))
-		return NULL;
-
 	if (dma_alloc_from_dev_coherent(dev, size, dma_handle, &cpu_addr))
 		return cpu_addr;