From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S266631AbUGPXjY (ORCPT ); Fri, 16 Jul 2004 19:39:24 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S266648AbUGPXjX (ORCPT ); Fri, 16 Jul 2004 19:39:23 -0400 Received: from rwcrmhc12.comcast.net ([216.148.227.85]:19403 "EHLO rwcrmhc12.comcast.net") by vger.kernel.org with ESMTP id S266631AbUGPXjV (ORCPT ); Fri, 16 Jul 2004 19:39:21 -0400 Message-ID: <40F86677.2070607@comcast.net> Date: Fri, 16 Jul 2004 16:36:23 -0700 From: "Amit D. Chaudhary" User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7) Gecko/20040616 X-Accept-Language: en-us, en MIME-Version: 1.0 To: dsaxena@plexity.net, linux-kernel@vger.kernel.org Subject: Re: MAX_DMA_ADDRESS in include/asm/asm-i386/dma.h (2.6.x and 2.4.x) References: <40F84A87.5050403@comcast.net> <20040716214721.GA20741@plexity.net> <40F852AE.8060703@comcast.net> <20040716222859.GA21647@plexity.net> In-Reply-To: <20040716222859.GA21647@plexity.net> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Deepak Saxena wrote: > 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. Thanks, noted and verified. This chip cannot DMA with a memory buffer returned by kmalloc without a GFP_DMA flag, that is memory addresses like 0xf67e0000, it works with 0xcxxx xxxx. I verified it by modifying the code and trying it out. >>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. This was a backup approach, I mentioned to provide details about the memory being allocated. I would like to avoid this approach. See reasons above. Amit