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:
  /* A piece of example */
  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:
  /* A piece of example */
  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>
---
Changelog
v1->v2:
 * Added new functions beside the old ones so we can replace callers
   one by one later.
 * Applied new functions to dma/direct.c only, because it's the best
   example caller to apply and should be safe with the new functions.

 include/linux/dma-contiguous.h | 10 +++++++
 kernel/dma/contiguous.c        | 48 ++++++++++++++++++++++++++++++++++
 kernel/dma/direct.c            | 24 +++--------------
 3 files changed, 62 insertions(+), 20 deletions(-)

diff --git a/include/linux/dma-contiguous.h b/include/linux/dma-contiguous.h
index f247e8aa5e3d..dacbdcb91a89 100644
--- a/include/linux/dma-contiguous.h
+++ b/include/linux/dma-contiguous.h

@@ -115,6 +115,8 @@ struct page *dma_alloc_from_contiguous(struct device *dev, size_t count,
                                       unsigned int order, bool no_warn);
 bool dma_release_from_contiguous(struct device *dev, struct page *pages,
                                 int count);
+struct page *dma_alloc_contiguous(struct device *dev, size_t size, gfp_t gfp);
+void dma_free_contiguous(struct device *dev, struct page *page, size_t size);

 #else

@@ -157,6 +159,14 @@ bool dma_release_from_contiguous(struct device *dev, struct page *pages,
        return false;
 }

+struct page *dma_alloc_contiguous(struct device *dev, size_t size, gfp_t gfp)
+{
+       return NULL;
+}
+
+static inline
+void dma_free_contiguous(struct device *dev, struct page *page, size_t size) { }
+
 #endif

 #endif

diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c
index b2a87905846d..21f39a6cb04f 100644
--- a/kernel/dma/contiguous.c
+++ b/kernel/dma/contiguous.c

@@ -214,6 +214,54 @@ 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
  */

diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index 2c2772e9702a..0816c1e8b05a 100644
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c

@@ -96,8 +96,6 @@ static bool dma_coherent_ok(struct device *dev, phys_addr_t phys, size_t size)
 struct page *__dma_direct_alloc_pages(struct device *dev, size_t size,
                dma_addr_t *dma_handle, gfp_t gfp, unsigned long attrs)
 {
-       unsigned int count = PAGE_ALIGN(size) >> PAGE_SHIFT;
-       int page_order = get_order(size);
        struct page *page = NULL;
        u64 phys_mask;

@@ -109,20 +107,9 @@ struct page *__dma_direct_alloc_pages(struct device *dev, size_t size,
        gfp |= __dma_direct_optimal_gfp_mask(dev, dev->coherent_dma_mask,
                        &phys_mask);
 again:
-       /* CMA can be used only in the context which permits sleeping */
-       if (gfpflags_allow_blocking(gfp)) {
-               page = dma_alloc_from_contiguous(dev, count, page_order,
-                                                gfp & __GFP_NOWARN);
-               if (page && !dma_coherent_ok(dev, page_to_phys(page), size)) {
-                       dma_release_from_contiguous(dev, page, count);
-                       page = NULL;
-               }
-       }
-       if (!page)
-               page = alloc_pages_node(dev_to_node(dev), gfp, page_order);
-
+       page = dma_alloc_contiguous(dev, size, gfp);
        if (page && !dma_coherent_ok(dev, page_to_phys(page), size)) {
-               __free_pages(page, page_order);
+               dma_free_contiguous(dev, page, size);
                page = NULL;

                if (IS_ENABLED(CONFIG_ZONE_DMA32) &&

@@ -154,7 +141,7 @@ void *dma_direct_alloc_pages(struct device *dev, size_t size,
        if (PageHighMem(page)) {
                /*
                 * Depending on the cma= arguments and per-arch setup
-                * dma_alloc_from_contiguous could return highmem pages.
+                * dma_alloc_contiguous could return highmem pages.
                 * Without remapping there is no way to return them here,
                 * so log an error and fail.
                 */

@@ -176,10 +163,7 @@ void *dma_direct_alloc_pages(struct device *dev, size_t size,

 void __dma_direct_free_pages(struct device *dev, size_t size, struct page *page)
 {
-       unsigned int count = PAGE_ALIGN(size) >> PAGE_SHIFT;
-
-       if (!dma_release_from_contiguous(dev, page, count))
-               __free_pages(page, get_order(size));
+       dma_free_contiguous(dev, page, size);
 }

 void dma_direct_free_pages(struct device *dev, size_t size, void *cpu_addr,
--

2.17.1


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