From mboxrd@z Thu Jan 1 00:00:00 1970 From: Greg KH Subject: Re: [PATCH 1/1] Userspace I/O (UIO): Add support for userspace DMA (corrected) Date: Wed, 3 Dec 2008 20:17:39 -0800 Message-ID: <20081204041739.GA16329@suse.de> References: <208aa0f00812031751n27a75d21h8747054651639463@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <208aa0f00812031751n27a75d21h8747054651639463-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org> Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Edward Estabrook Cc: linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, hjk-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org, edward.estabrook-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, edward_estabrook-+2HdxjxtzLdBDgjK7y7TUQ@public.gmane.org List-Id: linux-api@vger.kernel.org On Wed, Dec 03, 2008 at 05:51:30PM -0800, Edward Estabrook wrote: > From: Edward Estabrook > > Here is a patch that adds the ability to dynamically allocate and use > coherent DMA > from userspace by extending the Userspace IO driver. This patch applies against > 2.6.28-rc6. > > 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). > > The kernel-api change is that passing an offset value of 0xFFFFF000UL > to the a uio > device's mmap operation will dynamically allocate a DMA region. This > cannot change/ > break existing behavior as the previous UIO code only allowed a maximum of 5 > mappings. Odd formatting of your paragraphs :( Anyway, what about 64bit processors? What happens if they try to use a valid address in this range? Is this value always an "invalid" value for all arches that Linux runs on? thanks, greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html