[RFC] ARM: DMA coherent allocator: align remapped addresses

Commit Message

Russell King - ARM Linux July 25, 2010, 1:50 p.m. UTC

None

Patch

diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index 9e7742f..c704eed 100644
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c
@@ -183,6 +183,8 @@  static void *
 __dma_alloc_remap(struct page *page, size_t size, gfp_t gfp, pgprot_t prot)
 {
 	struct arm_vmregion *c;
+	size_t align;
+	int bit;
 
 	if (!consistent_pte[0]) {
 		printk(KERN_ERR "%s: not initialised\n", __func__);
@@ -191,9 +193,20 @@  __dma_alloc_remap(struct page *page, size_t size, gfp_t gfp, pgprot_t prot)
 	}
 
 	/*
+	 * Align the virtual region allocation - maximum alignment is
+	 * a section size, minimum is a page size.  This helps reduce
+	 * fragmentation of the DMA space, and also prevents allocations
+	 * smaller than a section from crossing a section boundary.
+	 */
+	bit = fls(size - 1) + 1;
+	if (bit > SECTION_SHIFT)
+		bit = SECTION_SHIFT;
+	align = 1 << bit;
+
+	/*
 	 * Allocate a virtual address in the consistent mapping region.
 	 */
-	c = arm_vmregion_alloc(&consistent_head, size,
+	c = arm_vmregion_alloc(&consistent_head, align, size,
 			    gfp & ~(__GFP_DMA | __GFP_HIGHMEM));
 	if (c) {
 		pte_t *pte;
diff --git a/arch/arm/mm/vmregion.c b/arch/arm/mm/vmregion.c
index 19e09bd..935993e 100644
--- a/arch/arm/mm/vmregion.c
+++ b/arch/arm/mm/vmregion.c
@@ -35,7 +35,8 @@ 
  */
 
 struct arm_vmregion *
-arm_vmregion_alloc(struct arm_vmregion_head *head, size_t size, gfp_t gfp)
+arm_vmregion_alloc(struct arm_vmregion_head *head, size_t align,
+		   size_t size, gfp_t gfp)
 {
 	unsigned long addr = head->vm_start, end = head->vm_end - size;
 	unsigned long flags;
@@ -58,7 +59,7 @@  arm_vmregion_alloc(struct arm_vmregion_head *head, size_t size, gfp_t gfp)
 			goto nospc;
 		if ((addr + size) <= c->vm_start)
 			goto found;
-		addr = c->vm_end;
+		addr = ALIGN(c->vm_end, align);
 		if (addr > end)
 			goto nospc;
 	}
diff --git a/arch/arm/mm/vmregion.h b/arch/arm/mm/vmregion.h
index 6b2cdbd..15e9f04 100644
--- a/arch/arm/mm/vmregion.h
+++ b/arch/arm/mm/vmregion.h
@@ -21,7 +21,7 @@  struct arm_vmregion {
 	int			vm_active;
 };
 
-struct arm_vmregion *arm_vmregion_alloc(struct arm_vmregion_head *, size_t, gfp_t);
+struct arm_vmregion *arm_vmregion_alloc(struct arm_vmregion_head *, size_t, size_t, gfp_t);
 struct arm_vmregion *arm_vmregion_find(struct arm_vmregion_head *, unsigned long);
 struct arm_vmregion *arm_vmregion_find_remove(struct arm_vmregion_head *, unsigned long);
 void arm_vmregion_free(struct arm_vmregion_head *, struct arm_vmregion *);