From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S266613AbUGPW3S (ORCPT ); Fri, 16 Jul 2004 18:29:18 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S266627AbUGPW3S (ORCPT ); Fri, 16 Jul 2004 18:29:18 -0400 Received: from sccrmhc12.comcast.net ([204.127.202.56]:23001 "EHLO sccrmhc12.comcast.net") by vger.kernel.org with ESMTP id S266613AbUGPW3A (ORCPT ); Fri, 16 Jul 2004 18:29:00 -0400 Date: Fri, 16 Jul 2004 15:28:59 -0700 From: Deepak Saxena To: "Amit D. Chaudhary" Cc: linux-kernel@vger.kernel.org Subject: Re: MAX_DMA_ADDRESS in include/asm/asm-i386/dma.h (2.6.x and 2.4.x) Message-ID: <20040716222859.GA21647@plexity.net> Reply-To: dsaxena@plexity.net References: <40F84A87.5050403@comcast.net> <20040716214721.GA20741@plexity.net> <40F852AE.8060703@comcast.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <40F852AE.8060703@comcast.net> Organization: Plexity Networks User-Agent: Mutt/1.5.5.1+cvs20040105i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Jul 16 2004, at 15:11, Amit D. Chaudhary was caught saying: > Deepak, > > I am missing what you are directing me to. > > If it is, > pci_alloc_consistent(), linux-2.4.25/arch/i386/kernel/pci-dma.c > dma_alloc_coherent(), linux-2.6.8-rc1/arch/i386/kernel/pci-dma.c > > They internally seem to __get_free_pages() Correct, but take a second look at the code (2.6): void *ret; /* ignore region specifiers */ gfp &= ~(__GFP_DMA | __GFP_HIGHMEM); if (dev == NULL || (dev->coherent_dma_mask < 0xffffffff)) gfp |= GFP_DMA; ret = (void *)__get_free_pages(gfp, get_order(size)); It uses GFP_DMA iff your coherent_dma_mask is != 0xffffffff. Assuming your device can address a the full 32-bit PCI address space, you need to set the coherent_dma_mask appropriately and you will get buffers from all addressable lowmem. I don't do much x86, so not sure how you go about allocating highmem DMA buffers. > The memory need not be page size, as a matter of fact, using a large > consecutive block, for example using alloc_bootmem_low() during kernel > bootup, will simplify the data transfer and result in no internal > fragmentation, it does introduce inflexibility in changing the size and > other issues. If you are using alloc_bootmem_low(), all you should have to do after allocating the memory is call pci_dma_map_single()/map_sg() to get PCI-DMA addresses. You still should have no reason to touch MAX_DMA_ADDRESS. ~Deepak -- Deepak Saxena - dsaxena at plexity dot net - http://www.plexity.net/ "Unlike me, many of you have accepted the situation of your imprisonment and will die here like rotten cabbages." - Number 6