AW:dma direction

[Johannes Thoma]

It might have to do something with CPU caching, we once had an issue with a USB driver where memory got overwritten. But I also might be wrong don't have the code at hand at the moment.

Best,

Johannes

-------- Originalnachricht --------
Betreff: dma direction
Von: Ran Shalit
An: kernelnewbies
Cc:

Hello,

I read the DMA-API-HOWTO
https://www.kernel.org/doc/Documentation/DMA-API-HOWTO.txt
Which mainly talks about dma mapping APIs.

But I don't understand what's the meaning of DMA direction in context
of mapping.
As I understand this documentation talks about mapping of dma buffers
- NOT about triggering dma copy.
In order to do a dma copy, we should use sometlink like dmaengine, Right ?

So if dma mapping is not concerned with copying dma from cpu to device
(or vice versa), why does it talks about dma direction ?

Thanks,
Ran

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