linux-kernel - Re: [PATCH 1/1] Userspace I/O (UIO): Add support for userspace DMA

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Date:	Fri, 11 Dec 2009 16:02:17 -0800
From:	Earl Chew <earl_chew@...lent.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	linux-kernel@...r.kernel.org, hjk@...utronix.de, gregkh@...e.de,
	hugh <hugh@...itas.com>, linux-mm <linux-mm@...ck.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 1/1] Userspace I/O (UIO): Add support for userspace DMA

I'm taking another look at the changes that were submitted in

http://lkml.org/lkml/2008/12/3/453

to see if they can be made more palatable.

In http://lkml.org/lkml/2008/12/4/64 you wrote:

> Why not create another special device that will give you DMA memory when
> you mmap it? That would also allow you to obtain the physical address
> without this utter horrid hack of writing it in the mmap'ed memory.
> 
> /dev/uioN-dma would seem like a fine name for that.

I understand the main objection was the hack to return the physical
address of the allocated DMA buffer within the buffer itself amongst
some other things.

Your suggestion was to create /dev/uioN-dma for the purpose of
allocating DMA memory.

I'm having trouble figuring out how this would help to return the
physical (bus) address of the DMA memory in a more elegant manner.

What idea did you have for the userspace program to obtain
the physical (bus) of the allocated DMA memory buffer?

Earl

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