Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932301AbWCBVEy (ORCPT ); Thu, 2 Mar 2006 16:04:54 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932537AbWCBVEy (ORCPT ); Thu, 2 Mar 2006 16:04:54 -0500 Received: from mail0.lsil.com ([147.145.40.20]:30112 "EHLO mail0.lsil.com") by vger.kernel.org with ESMTP id S932301AbWCBVEx convert rfc822-to-8bit (ORCPT ); Thu, 2 Mar 2006 16:04:53 -0500 X-MimeOLE: Produced By Microsoft Exchange V6.5 Content-class: urn:content-classes:message MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT Subject: RE: Question: how to map SCSI data DMA address to virtual address? Date: Thu, 2 Mar 2006 14:04:48 -0700 Message-ID: <9738BCBE884FDB42801FAD8A7769C2651420C5@NAMAIL1.ad.lsil.com> X-MS-Has-Attach: X-MS-TNEF-Correlator: Thread-Topic: Question: how to map SCSI data DMA address to virtual address? Thread-index: AcY+NG74O2RlmuLlQfiZHI7NABNhpwABxTgg From: "Ju, Seokmann" To: "linux-os \(Dick Johnson\)" , "Jens Axboe" Cc: "Linux kernel" , X-OriginalArrivalTime: 02 Mar 2006 21:04:48.0842 (UTC) FILETIME=[F0F892A0:01C63E3C] Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2100 Lines: 67 Hi, On Thursday, March 02, 2006 3:04 PM Dick Johnson wrote: > On Thu, 2 Mar 2006, Jens Axboe wrote: > > > On Thu, Mar 02 2006, linux-os (Dick Johnson) wrote: > >> > >> On Thu, 2 Mar 2006, Ju, Seokmann wrote: > >> > >>> Hi, > >>> > >>> In the 'scsi_cmnd' structure, there are two entries > holding address > >>> information for data to be transferred. One is > 'request_buffer' and the > >>> other one is 'buffer'. > >>> In case of 'use_sg' is non-zero, those entries indicates > the address of > >>> the scatter-gather table. > >>> > >>> Is there way to get virtual address (so that the data > could be accessed > >>> by the driver) of the actual data in the case of 'use_sg' > is non-zero? > >>> > >>> Any comments would be appreciated. > >>> > >>> > >>> Thank you, > >>> > >>> Seokmann > >>> - > >> > >> There is a macro for this purpose. However, for experiments, in > >> the kernel, you can add PAGE_OFFSET (0xC00000000) to get > the virtual > >> address. The macro is __va(a), its inverse is __pa(a). > >> > >> Careful. These things can change. > > > > Bzzt no, this wont work if an iommu is involved. It also > wont work if > > the page doesn't have a virtual address mapping (think highmem). > > > > -- > > > Jens Axboe > > > > Are you going to get DMA-able pages out of high memory? The guy is > doing scatter-table DMA, i.e., linked DMA. I think you need to > build that table with pages from get_dma_page(). If you use > highmem, somebody can program the iommu right out from under > the DMA engine while a DMA is in progress because the CPU is > not involved and can be executing lots of code that can do lots > of bad things. Thank you for your valueable comment. One good thing is that the system does 2 GB memory so that highmem won't come into picture. I am implementing the feature with suggestions. Thank you again, Seokmann - 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/