From mboxrd@z Thu Jan  1 00:00:00 1970
From: greg@kroah.com (Greg KH)
Date: Tue, 20 Dec 2016 10:38:28 +0100
Subject: Driver to allow DMA from user space
In-Reply-To: <CAJ2oMhLdc0FqxL2KUQYKNey7podoztoZnuWuWMmtTJukfFvp=Q@mail.gmail.com>
References: <CAJ2oMhLdc0FqxL2KUQYKNey7podoztoZnuWuWMmtTJukfFvp=Q@mail.gmail.com>
Message-ID: <20161220093828.GA13045@kroah.com>
To: kernelnewbies@lists.kernelnewbies.org
List-Id: kernelnewbies.lists.kernelnewbies.org

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