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dma-mapping: move the dma_declare_coherent_memory documentation

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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 <hch@lst.de>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
This commit is contained in:
Christoph Hellwig 2020-08-18 19:32:42 +02:00
parent 545d29272f
commit a92df4f62f
2 changed files with 17 additions and 24 deletions
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24
Documentation/core-api/dma-api.rst
View File

@ -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
-------------------------------------------

17
kernel/dma/coherent.c
View File

@ -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)
{