From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mx1.redhat.com (ext-mx07.extmail.prod.ext.phx2.redhat.com [10.5.110.11]) by int-mx01.intmail.prod.int.phx2.redhat.com (8.13.8/8.13.8) with ESMTP id o65AAkjB028416 for ; Mon, 5 Jul 2010 06:10:46 -0400 Received: from moutng.kundenserver.de (moutng.kundenserver.de [212.227.126.186]) by mx1.redhat.com (8.13.8/8.13.8) with ESMTP id o65AAF2H019294 for ; Mon, 5 Jul 2010 06:10:36 -0400 Message-ID: <4C31AF7E.7090602@2net.co.uk> Date: Mon, 05 Jul 2010 11:10:06 +0100 From: Chris Simmonds MIME-Version: 1.0 To: video4linux-list@redhat.com Subject: Re: Contiguous memory allocations References: <1278103660.6034.16.camel@localhost> In-Reply-To: <1278103660.6034.16.camel@localhost> Reply-To: chris@2net.co.uk List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: video4linux-list-bounces@redhat.com Errors-To: video4linux-list-bounces@redhat.com List-ID: On 02/07/10 21:47, Eric Nelson wrote: > Does anyone know if there's a common infrastructure for allocation > of DMA'able memory by drivers and applications above the straight > kernel API (dma_alloc_coherent)? > > I'm working with Freescale i.MX51 drivers to do 720P video > input and output and the embedded calls to dma_alloc_coherent > fail except when used right after boot because of fragmentation. > > I'm fighting the urge to write yet another special-purpose allocator > for video buffers thinking this must be a common problem with a > solution already, but I can't seem to locate one. > > The closest thing I've found is the bigphysarea patch, which doesn't > appear to be supported or headed toward main-line. > > Thanks in advance, > dma_alloc_coherent is pretty much just a wrapper round get_free_pages, which is the lowest level allocator in the kernel. So, no there is no other option (but see below). The simplest thing is to make sure your driver is loaded at boot time and to grab all the memory you need then and never let it go. That's what I do. If you are desperate, you can use the bigphysarea patch - it's quite common on streaming video devices - but you will have to port it to your kernel. Or, you can restrict the memory the kernel uses with something like "mem=128M" on the command line and take that above 128M for yourself. You will have to map it in with ioremap(_nocache). Bye for now, Chris. -- Chris Simmonds 2net Limited chris@2net.co.uk http://www.2net.co.uk/ -- video4linux-list mailing list Unsubscribe mailto:video4linux-list-request@redhat.com?subject=unsubscribe https://www.redhat.com/mailman/listinfo/video4linux-list