ARM: DMA coherent allocator: align remapped addresses

The DMA coherent remap area is used to provide an uncached mapping
of memory for coherency with DMA engines.  Currently, we look for
any free hole which our allocation will fit in with page alignment.

However, this can lead to fragmentation of the area, and allows small
allocations to cross L1 entry boundaries.  This is undesirable as we
want to move towards allocating sections of memory.

Align allocations according to the size, limiting the alignment between
the page and section sizes.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

3 files changed, 18 insertions, 4 deletions

diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index 9e7742f0a102..c704eed63c5d 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 19e09bdb1b8a..935993e1b1ef 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 6b2cdbdf3a85..15e9f044db9f 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 *);