From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 4 Dec 2008 10:27:22 +0000 (GMT) From: Hugh Dickins Subject: Re: [PATCH 1/1] Userspace I/O (UIO): Add support for userspace DMA In-Reply-To: <1228379942.5092.14.camel@twins> Message-ID: References: <43FC624C55D8C746A914570B66D642610367F29B@cos-us-mb03.cos.agilent.com> <1228379942.5092.14.camel@twins> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org Return-Path: To: Peter Zijlstra Cc: edward_estabrook@agilent.com, linux-kernel@vger.kernel.org, hjk@linutronix.de, gregkh@suse.de, edward.estabrook@gmail.com, linux-mm , Thomas Gleixner List-ID: On Thu, 4 Dec 2008, Peter Zijlstra wrote: > On Wed, 2008-12-03 at 14:39 -0700, edward_estabrook@agilent.com wrote: > > > > The gist of this implementation is to overload uio's mmap > > functionality to allocate and map a new DMA region on demand. The > > bus-specific DMA address as returned by dma_alloc_coherent is made > > available to userspace in the 1st long word of the newly created > > region (as well as through the conventional 'addr' file in sysfs). > > > > To allocate a DMA region you use the following: > > /* Pass this magic number to mmap as offset to dynamically allocate a > > chunk of memory */ #define DMA_MEM_ALLOCATE_MMAP_OFFSET 0xFFFFF000UL > > ... > > Comments appreciated! > > Yuck! > > 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 couldn't agree more. It sounds fine as a local hack for Edward to try out some functionality he needed in a hurry; but as something that should enter the mainline kernel in that form - no. Hugh -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org