On Mon, Dec 19, 2016 at 06:08:47PM +0200, Ran Shalit wrote:

Hello,

I want to use DMA from userspace.

Why?

I already use dma in kernel, and now I want can create a character
device which will be responsible for this.

Why?

The only problem is that I want to use the same memory which was
allocated in kernel with dma_alloc_coherent.

Why?

Is it correct to use mmap in order to use the phsyical memory which
was allocated with dma_alloc_coherent ?

If it's that simple it can be surely helpful, and the simple driver
which wraps dma_alloc_coherent can do the job for dmaing from
userspace.

Have you looked at the uio driver interface?

But again, why?  What problem are you trying to solve here?

thanks,

greg k-h