From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from wproxy.gmail.com (wproxy.gmail.com [64.233.184.206]) by ozlabs.org (Postfix) with ESMTP id 12A3767A33 for ; Thu, 19 May 2005 10:54:40 +1000 (EST) Received: by wproxy.gmail.com with SMTP id 37so361959wra for ; Wed, 18 May 2005 17:54:39 -0700 (PDT) Message-ID: Date: Wed, 18 May 2005 17:54:39 -0700 From: Shawn Jin To: ppcembed Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Subject: DMA consistent allocation is limited to 2MB on 2.6.11 for ppc440? Reply-To: Shawn Jin List-Id: Linux on Embedded PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Hi, The page table 'consistent_pte' covers the uncached DMA consistent allocation space. Its size is only one page, each page has 512 PTEs. That means only 2MB memory are available for DMA. For some applications this is not enough. So how to eliminate this limitation? I noticed that there are two configuration macros related to this issue: CONFIG_CONSISTENT_START and CONFIG_CONSISTENT_SIZE. The current value for CONFIG_CONSISTENT_SIZE is 2MB, which is exactly able to be covered by one page. I guess that's why consistent_pte is initialized to just one page. So simply changing CONFIG_CONSISTENT_SIZE cannot remove the 2MB limitation. dma_alloc_init() has to be modified to initialize consisten_pte to some pages which are enough to cover CONFIG_CONSISTENT_SIZE memory space. Right? Does increasing CONSISTENT_SIZE have any side effects? Thanks, -Shawn.