From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andi Kleen Subject: Re: Query regarding modifying the DMA Mask based on the available memory in the system Date: Thu, 17 Apr 2008 17:06:50 +0200 Message-ID: <4807678A.8020906@firstfloor.org> References: <5AE055B67BB5764693E2900C7E3699BE010CAB76@pamail.ad.lsil.com> <1208441932.3150.4.camel@localhost.localdomain> <87iqygk0bu.fsf@basil.nowhere.org> <1208444622.3150.10.camel@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: Received: from one.firstfloor.org ([213.235.205.2]:47039 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758941AbYDQPGz (ORCPT ); Thu, 17 Apr 2008 11:06:55 -0400 In-Reply-To: <1208444622.3150.10.camel@localhost.localdomain> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: James Bottomley Cc: "Prakash, Sathya" , linux-scsi@vger.kernel.org James Bottomley wrote: > On Thu, 2008-04-17 at 16:44 +0200, Andi Kleen wrote: >>> For drivers that can alter their descriptor types, we have this >>> function: >>> >>> dma_get_required_mask() >> Are you sure we have it? It seems to be in drivers/base/platform.c >> conditional on ARCH_HAS_DMA_GET_REQUIRED_MASK, but according to my >> grep no architecture ever sets that flag. > > Yes ... positive. That's the default and correct implementation based > on the largest addressable physical memory. Ok but still the whole thing is completely useless right now. >> I don't think it would be very hard to implement on x86 at least, >> mind you. Just nobody seems to have done it so far. > > Really, only machines with IOMMUs that want to restrict this need > implement it. I don't think so. For once in the scenario described by the original poster it makes some sense even without IOMMU. -Andi