[18/28] dma-mapping: move the dma_declare_coherent_memory documentation

Commit Message

Christoph Hellwig Aug. 19, 2020, 6:55 a.m. UTC

dma_declare_coherent_memory should not be in a DMA API guide aimed
at driver writers (that is consumers of the API).  Move it to a comment
near the function instead.

Signed-off-by: Christoph Hellwig <[e-mail]>
---
 Documentation/core-api/dma-api.rst | 24 ------------------------
 kernel/dma/coherent.c              | 17 +++++++++++++++++
 2 files changed, 17 insertions(+), 24 deletions(-)

Patch

diff --git a/Documentation/core-api/dma-api.rst b/Documentation/core-api/dma-api.rst
index 3b3abbbb4b9a6f..90239348b30f6f 100644
--- a/Documentation/core-api/dma-api.rst
+++ b/Documentation/core-api/dma-api.rst
@@ -586,30 +586,6 @@  the DMA_ATTR_NON_CONSISTENT flag starting at virtual address vaddr and
 continuing on for size.  Again, you *must* observe the cache line
 boundaries when doing this.
 
-::
-
-	int
-	dma_declare_coherent_memory(struct device *dev, phys_addr_t phys_addr,
-				    dma_addr_t device_addr, size_t size);
-
-Declare region of memory to be handed out by dma_alloc_coherent() when
-it's asked for coherent memory for this device.
-
-phys_addr is the CPU physical address to which the memory is currently
-assigned (this will be ioremapped so the CPU can access the region).
-
-device_addr is the DMA address the device needs to be programmed
-with to actually address this memory (this will be handed out as the
-dma_addr_t in dma_alloc_coherent()).
-
-size is the size of the area (must be multiples of PAGE_SIZE).
-
-As a simplification for the platforms, only *one* such region of
-memory may be declared per device.
-
-For reasons of efficiency, most platforms choose to track the declared
-region only at the granularity of a page.  For smaller allocations,
-you should use the dma_pool() API.
 
 Part III - Debug drivers use of the DMA-API
 -------------------------------------------
diff --git a/kernel/dma/coherent.c b/kernel/dma/coherent.c
index 2a0c4985f38e41..f85d14bbfcbe03 100644
--- a/kernel/dma/coherent.c
+++ b/kernel/dma/coherent.c
@@ -107,6 +107,23 @@  static int dma_assign_coherent_memory(struct device *dev,
 	return 0;
 }
 
+/*
+ * Declare a region of memory to be handed out by dma_alloc_coherent() when it
+ * is asked for coherent memory for this device.  This shall only be used
+ * from platform code, usually based on the device tree description.
+ * 
+ * phys_addr is the CPU physical address to which the memory is currently
+ * assigned (this will be ioremapped so the CPU can access the region).
+ *
+ * device_addr is the DMA address the device needs to be programmed with to
+ * actually address this memory (this will be handed out as the dma_addr_t in
+ * dma_alloc_coherent()).
+ *
+ * size is the size of the area (must be a multiple of PAGE_SIZE).
+ *
+ * As a simplification for the platforms, only *one* such region of memory may
+ * be declared per device.
+ */
 int dma_declare_coherent_memory(struct device *dev, phys_addr_t phys_addr,
 				dma_addr_t device_addr, size_t size)
 {