Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752570AbbGVUUy (ORCPT ); Wed, 22 Jul 2015 16:20:54 -0400 Received: from smtp4-g21.free.fr ([212.27.42.4]:26899 "EHLO smtp4-g21.free.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750910AbbGVUUx (ORCPT ); Wed, 22 Jul 2015 16:20:53 -0400 Message-ID: <55AFFB1E.5050405@free.fr> Date: Wed, 22 Jul 2015 22:20:46 +0200 From: Mason User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:36.0) Gecko/20100101 Firefox/36.0 SeaMonkey/2.33.1 MIME-Version: 1.0 To: Laura Abbott , Linux ARM CC: LKML Subject: Re: Having Linux handle different "types" of memory References: <55AFB47B.301@free.fr> <55AFC324.9010401@redhat.com> In-Reply-To: <55AFC324.9010401@redhat.com> Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2338 Lines: 59 On 22/07/2015 18:21, Laura Abbott wrote: > On 07/22/2015 08:19 AM, Mason wrote: > >> I'm using an ARMv7 platform (Cortex A9) on Linux 3.14 >> >> The system supports two memory modules. >> >> For performance reasons, memory is "transparently" interleaved >> (with a 128-byte grain). That is, when the CPU accesses addresses >> 0-127, it hits DRAM0; addresses 128-255, it hits DRAM1, and so on. >> >> The problem is that other devices in the system, mainly the >> Ethernet controller, didn't get the "transparent interleaving" >> treatment. They just see DRAM0 and DRAM1. And I'm guessing this >> will generate all kinds of "interesting" problems when I try to >> DMA from the Ethernet controller's memory to DRAM... >> >> Is there a way to tell Linux: >> >> 1) this 1GB memory chunk here is for you and your private allocations, >> but don't use it for talking to devices/peripherals. >> >> 2) this 1GB memory chunk there is for talking to devices/peripherals, >> but it has lower performance, so try not to use it for your own >> private memory pools, but you can if memory is /really/ tight. >> >> Is there something like this? >> >> Maybe one of the NUMA policies? >> https://www.kernel.org/doc/Documentation/vm/numa_memory_policy.txt >> (I don't see any arch/arm/mm/numa.c however) >> >> Maybe I can pretend that there is some kind of IOMMU? >> https://www.kernel.org/doc/Documentation/DMA-API-HOWTO.txt >> arch/arm/include/asm/dma-iommu.h >> >> Or maybe there is an obvious solution that I'm missing? > > I don't think there is an easy solution right now. This is still > an open problem as far as I know. You might look into whether > marking one of the regions as a CMA region would allow you the > control you need. I have control of the address ranges where memory is interleaved, and where it is not. Is it possible to force (some) memory allocations to only come from the latter pool? I'm thinking another possibility is to not even give control of the non-interleaved zone to Linux, and just ioremap it as needed. (But then, it's not available when memory is tight.) Regards. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/