From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Wed, 30 May 2001 11:13:25 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Wed, 30 May 2001 11:13:15 -0400 Received: from mtiwmhc22.worldnet.att.net ([204.127.131.47]:43516 "EHLO mtiwmhc22.worldnet.att.net") by vger.kernel.org with ESMTP id convert rfc822-to-8bit; Wed, 30 May 2001 11:13:07 -0400 From: William Waddington To: linux-kernel@vger.kernel.org Subject: Re: query regarding 'map_user_kiobuf' Date: Wed, 30 May 2001 08:12:17 -0700 Message-ID: <593aht81ed3p199mr0l1m896d32bgr6qnv@4ax.com> In-Reply-To: In-Reply-To: X-Mailer: Forte Agent 1.8/32.548 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 29 May 2001 19:30:06 GMT, in fa.linux.kernel you wrote: > >mdaljeet@in.ibm.com said: >> After using the 'map_user_kiobuf', I observed the followiing: >> >> 1. 'kiobuf->maplist[0]->virtual' contains a different virtual address than >> the user space buffer address >> 2. But these two addresses are mapped as when i write something using the >> address 'kiobuf->maplist[0]->virtual' inside the kernel, I see the same >> data in the user space buffer in my application. >> 3. I use the 'virt_to_phys' operation to the virtual address >> 'kiobuf->maplist[0]->virtual' to get the physical address. >> 4. I use this physical address for DMA operations. >> >> Now, using this information I do a DMA from card to system memory. What I >> have noticed is that DMA happens somewhere else in the system memory. I am >> not able to execute most of the commands (ls, chmod, cat, clear etc) after >> my user program exits. >> >> Am I doing the steps 3 and 4 above right? > >After calling map_user_kiobuf(), I believe you should be locking the pages >in memory by calling lock_kiovec(). Otherwise, nothing prevents them from >being paged out again. > >Also, the pages may be in high memory and not directly accessible. You should >use kmap() before touching them from the kernel rather than just using >page->virtual, and obviously kunmap() afterwards. > >The PCI DMA interface is more complex than simply using virt_to_phys() too, >if you want to deal correctly with the highmem case. I'm sure others will >give you the details or pointers to the documentation. David, I have a couple of user DMA drivers up and running, but in light of your comment, I am not so sure. I see the following w/map_user_kiobuf() in memory.c (2.4.4) ... /* * Force in an entire range of pages from the current process's user VA, * and pin them in physical memory. */ #define dprintk(x...) int map_user_kiobuf(int rw, struct kiobuf *iobuf, unsigned long va, size_t len) ... What is the difference between pinning and locking? I had the impression that locking had more to do with ownership. Thanks, Bill --------------------------------------- Bill Waddington Bainbridge Island, WA, USA csbwaddington@att.net ikoncorp@att.net ---------------------------------------