Linux DMA API Questions

[Mj Embd]

Following the text at
https://www.kernel.org/doc/Documentation/DMA-API.txt a few inlined
questions

Part Ia - Using large dma-coherent buffers
------------------------------------------

void *
dma_alloc_coherent(struct device *dev, size_t size,
                 dma_addr_t *dma_handle, gfp_t flag)

Consistent memory is memory for which a write by either the device or
the processor can immediately be read by the processor or device
without having to worry about caching effects.  (You may however need
to make sure to flush the processor's write buffers before telling
devices to read that memory.)

Q1. Is it safe to assume that the area allocated is cacheable ? As the
last line state that flushing is required

Q1a. Does this API allocate memory from lower 16MB which is considered DMA safe.

dma_addr_t
dma_map_single(struct device *dev, void *cpu_addr, size_t size,
              enum dma_data_direction direction)

Maps a piece of processor virtual memory so it can be accessed by the
device and returns the physical handle of the memory.

The direction for both api's may be converted freely by casting.
However the dma_ API uses a strongly typed enumerator for its
direction:

DMA_NONE        no direction (used for debugging)
DMA_TO_DEVICE       data is going from the memory to the device
DMA_FROM_DEVICE     data is coming from the device to the memory
DMA_BIDIRECTIONAL   direction isn't known

Q2. Does the DMA_XXX options direct change of Page Attributes for the
VA=>PA mapping. Say DMA_TO_DEVICE would mark the area as non-cacheable
?



-- 
-mj