linux-kernel - [PATCH 2/8] dma-mapping: document dma_{alloc,free}

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Date:   Wed, 30 Sep 2020 18:09:11 +0200
From:   Christoph Hellwig <hch@....de>
To:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Tomasz Figa <tfiga@...omium.org>,
        iommu@...ts.linux-foundation.org
Cc:     Robin Murphy <robin.murphy@....com>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org
Subject: [PATCH 2/8] dma-mapping: document dma_{alloc,free}_pages

Document the new dma_alloc_pages and dma_free_pages APIs, and fix
up the documentation for dma_alloc_noncoherent and dma_free_noncoherent.

Reported-by: Robin Murphy <robin.murphy@....com>
Signed-off-by: Christoph Hellwig <hch@....de>
---
 Documentation/core-api/dma-api.rst | 45 ++++++++++++++++++++++++++----
 1 file changed, 40 insertions(+), 5 deletions(-)

diff --git a/Documentation/core-api/dma-api.rst b/Documentation/core-api/dma-api.rst
index ea0413276ddb70..a75c469dbcaa7c 100644
--- a/Documentation/core-api/dma-api.rst
+++ b/Documentation/core-api/dma-api.rst
@@ -534,11 +534,9 @@ an I/O device, you should not be using this part of the API.
 			dma_addr_t *dma_handle, enum dma_data_direction dir,
 			gfp_t gfp)
 
-This routine allocates a region of <size> bytes of consistent memory.  It
+This routine allocates a region of <size> bytes of non-coherent memory.  It
 returns a pointer to the allocated region (in the processor's virtual address
-space) or NULL if the allocation failed.  The returned memory may or may not
-be in the kernels direct mapping.  Drivers must not call virt_to_page on
-the returned memory region.
+space) or NULL if the allocation failed.
 
 It also returns a <dma_handle> which may be cast to an unsigned integer the
 same width as the bus and given to the device as the DMA address base of
@@ -565,7 +563,44 @@ reused.
 Free a region of memory previously allocated using dma_alloc_noncoherent().
 dev, size and dma_handle and dir must all be the same as those passed into
 dma_alloc_noncoherent().  cpu_addr must be the virtual address returned by
-the dma_alloc_noncoherent().
+dma_alloc_noncoherent().
+
+::
+
+	struct page *
+	dma_alloc_pages(struct device *dev, size_t size, dma_addr_t *dma_handle,
+			enum dma_data_direction dir, gfp_t gfp)
+
+This routine allocates a region of <size> bytes of non-coherent memory.  It
+returns a pointer to first struct page for the region, or NULL if the
+allocation failed.
+
+It also returns a <dma_handle> which may be cast to an unsigned integer the
+same width as the bus and given to the device as the DMA address base of
+the region.
+
+The dir parameter specified if data is read and/or written by the device,
+see dma_map_single() for details.
+
+The gfp parameter allows the caller to specify the ``GFP_`` flags (see
+kmalloc()) for the allocation, but rejects flags used to specify a memory
+zone such as GFP_DMA or GFP_HIGHMEM.
+
+Before giving the memory to the device, dma_sync_single_for_device() needs
+to be called, and before reading memory written by the device,
+dma_sync_single_for_cpu(), just like for streaming DMA mappings that are
+reused.
+
+::
+
+	void
+	dma_free_pages(struct device *dev, size_t size, struct page *page,
+			dma_addr_t dma_handle, enum dma_data_direction dir)
+
+Free a region of memory previously allocated using dma_alloc_pages().
+dev, size and dma_handle and dir must all be the same as those passed into
+dma_alloc_noncoherent().  page must be the pointer returned by
+dma_alloc_pages().
 
 ::
 
-- 
2.28.0