dma-contiguous: add dma_{alloc,free}_contiguous() helpers

Both dma_alloc_from_contiguous() and dma_release_from_contiguous() are
very simply implemented, but requiring callers to pass certain
parameters like count and align, and taking a boolean parameter to check
__GFP_NOWARN in the allocation flags. So every function call duplicates
similar work:

	unsigned long order = get_order(size);
	size_t count = size >> PAGE_SHIFT;

	page = dma_alloc_from_contiguous(dev, count, order,
			gfp & __GFP_NOWARN);

	[...]

	dma_release_from_contiguous(dev, page, size >> PAGE_SHIFT);

Additionally, as CMA can be used only in the context which permits
sleeping, most of callers do a gfpflags_allow_blocking() check and a
corresponding fallback allocation of normal pages upon any false result:

	if (gfpflags_allow_blocking(flag))
		page = dma_alloc_from_contiguous();
	if (!page)
		page = alloc_pages();

	[...]

	if (!dma_release_from_contiguous(dev, page, count))
		__free_pages(page, get_order(size));

So this patch simplifies those function calls by abstracting these
operations into the two new functions: dma_{alloc,free}_contiguous.

As some callers of dma_{alloc,release}_from_contiguous() might be
complicated, this patch just implements these two new functions to
kernel/dma/direct.c only as an initial step.

Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Nicolin Chen <nicoleotsuka@gmail.com>
Tested-by: dann frazier <dann.frazier@canonical.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

1 files changed, 47 insertions, 0 deletions

diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c
index b2a87905846d..637b120d647b 100644
--- a/kernel/dma/contiguous.c
+++ b/kernel/dma/contiguous.c
@@ -214,6 +214,53 @@ bool dma_release_from_contiguous(struct device *dev, struct page *pages,
 	return cma_release(dev_get_cma_area(dev), pages, count);
 }
 
+/**
+ * dma_alloc_contiguous() - allocate contiguous pages
+ * @dev:   Pointer to device for which the allocation is performed.
+ * @size:  Requested allocation size.
+ * @gfp:   Allocation flags.
+ *
+ * This function allocates contiguous memory buffer for specified device. It
+ * first tries to use device specific contiguous memory area if available or
+ * the default global one, then tries a fallback allocation of normal pages.
+ */
+struct page *dma_alloc_contiguous(struct device *dev, size_t size, gfp_t gfp)
+{
+	int node = dev ? dev_to_node(dev) : NUMA_NO_NODE;
+	size_t count = PAGE_ALIGN(size) >> PAGE_SHIFT;
+	size_t align = get_order(PAGE_ALIGN(size));
+	struct cma *cma = dev_get_cma_area(dev);
+	struct page *page = NULL;
+
+	/* CMA can be used only in the context which permits sleeping */
+	if (cma && gfpflags_allow_blocking(gfp)) {
+		align = min_t(size_t, align, CONFIG_CMA_ALIGNMENT);
+		page = cma_alloc(cma, count, align, gfp & __GFP_NOWARN);
+	}
+
+	/* Fallback allocation of normal pages */
+	if (!page)
+		page = alloc_pages_node(node, gfp, align);
+	return page;
+}
+
+/**
+ * dma_free_contiguous() - release allocated pages
+ * @dev:   Pointer to device for which the pages were allocated.
+ * @page:  Pointer to the allocated pages.
+ * @size:  Size of allocated pages.
+ *
+ * This function releases memory allocated by dma_alloc_contiguous(). As the
+ * cma_release returns false when provided pages do not belong to contiguous
+ * area and true otherwise, this function then does a fallback __free_pages()
+ * upon a false-return.
+ */
+void dma_free_contiguous(struct device *dev, struct page *page, size_t size)
+{
+	if (!cma_release(dev_get_cma_area(dev), page, size >> PAGE_SHIFT))
+		__free_pages(page, get_order(size));
+}
+
 /*
  * Support for reserved memory regions defined in device tree
  */