Hi Mark!
>
> Drivers can supply pre-mapped DMA buffers if they set is_dma_mapped
> which is about as good as you get with dmaengine at the minute. The
> main opportunities for enhancement here are in the master interface
> rather than the client, at least as things stand.
This is part of my pre-requisite for making it prepareable in my case...
Because otherwise you have (again) to walk the tree to set the rx_dma
via dma_map_single and here the API explicitly states that between the map
and unmap call the caller may NOT access the pages.
The reason is (probably) for old-ISA devices that may only DMA map 24 bit
addresses. So the map/unmap actually is supposed to copy data to a bounce
buffer and back (depending on the direction given).
Typically not an issue on ARM though, I would say...
Hence this becomes expensive to map and then creating the "whole" thing
works just as fine.
Ciao,
Martin
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