Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756730AbcKKOoe (ORCPT ); Fri, 11 Nov 2016 09:44:34 -0500 Received: from foss.arm.com ([217.140.101.70]:44800 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756108AbcKKOoc (ORCPT ); Fri, 11 Nov 2016 09:44:32 -0500 Subject: Re: [PATCH v6 05/07] iommu/ipmmu-vmsa: Add new IOMMU_DOMAIN_DMA ops To: Laurent Pinchart References: <20161019233533.10506.16810.sendpatchset@little-apple> <20161019233623.10506.49016.sendpatchset@little-apple> <941ff264-8f9f-e0e6-2b50-bdd3e19946e5@arm.com> <16618395.kRQakkIJXR@avalon> Cc: Magnus Damm , iommu@lists.linux-foundation.org, laurent.pinchart+renesas@ideasonboard.com, geert+renesas@glider.be, joro@8bytes.org, linux-kernel@vger.kernel.org, linux-renesas-soc@vger.kernel.org, horms+renesas@verge.net.au, m.szyprowski@samsung.com From: Robin Murphy Message-ID: Date: Fri, 11 Nov 2016 14:44:29 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0 MIME-Version: 1.0 In-Reply-To: <16618395.kRQakkIJXR@avalon> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2830 Lines: 88 Hi Laurent, On 11/11/16 01:50, Laurent Pinchart wrote: > Hi Robin, > > On Friday 21 Oct 2016 18:52:53 Robin Murphy wrote: >> On 20/10/16 00:36, Magnus Damm wrote: >>> From: Magnus Damm >>> >>> Introduce an alternative set of iommu_ops suitable for 64-bit ARM >>> as well as 32-bit ARM when CONFIG_IOMMU_DMA=y. Also adjust the >>> Kconfig to depend on ARM or IOMMU_DMA. >>> >>> Signed-off-by: Magnus Damm >>> --- >>> >>> Changes since V5: >>> - Made domain allocation/free code more consistent - thanks Joerg! >>> >>> Changes since V4: >>> - Added Kconfig hunk to depend on ARM or IOMMU_DMA >>> >>> Changes since V3: >>> - Removed group parameter from ipmmu_init_platform_device() >>> >>> Changes since V2: >>> >>> - Included this new patch from the following series: >>> [PATCH 00/04] iommu/ipmmu-vmsa: IPMMU CONFIG_IOMMU_DMA update >>> >>> - Use only a single iommu_ops structure with #ifdef CONFIG_IOMMU_DMA >>> - Folded in #ifdefs to handle CONFIG_ARM and CONFIG_IOMMU_DMA >>> - of_xlate() is now used without #ifdefs >>> - Made sure code compiles on both 32-bit and 64-bit ARM. >>> >>> drivers/iommu/Kconfig | 1 >>> drivers/iommu/ipmmu-vmsa.c | 122 ++++++++++++++++++++++++++++++++++++--- >>> 2 files changed, 115 insertions(+), 8 deletions(-) > > [snip] > >>> --- 0006/drivers/iommu/ipmmu-vmsa.c >>> +++ work/drivers/iommu/ipmmu-vmsa.c 2016-10-20 08:16:48.440607110 +0900 > > [snip] > >>> -static struct iommu_domain *ipmmu_domain_alloc(unsigned type) >>> -{ >>> - if (type != IOMMU_DOMAIN_UNMANAGED) >>> - return NULL; >> >> I *think* that if we did the initial check thus: >> >> if (type != IOMMU_DOMAIN_UNMANAGED || >> (IS_ENABLED(CONFIG_IOMMU_DMA) && type != IOMMU_DOMAIN_DMA)) >> return NULL; > > I assume you meant > > if (type != IOMMU_DOMAIN_UNMANAGED && > (!IS_ENABLED(CONFIG_IOMMU_DMA) || type != IOMMU_DOMAIN_DMA)) > return NULL; > > But how about just > > if (type != IOMMU_DOMAIN_UNMANAGED && type != IOMMU_DOMAIN_DMA)) > return NULL; > > as type will never be set to IOMMU_DOMAIN_DMA on ARM32 ? Actually it can be, but *only* at this point, because iommu_group_get_for_dev() will always attempt to allocate a default domain. Having the additional check up-front just saves going through the whole IOVA domain allocation only to tear it all down again when get_cookie() returns -ENODEV. You're right that it's not strictly necessary (and that I got my DeMorganning wrong), though. Robin. >> it shouldn't be necessary to split the function at all - we then just >> wrap the {get,put}_cookie() bits in "if (type == IOMMU_DOMAIN_DMA)" and >> in the 32-bit ARM case they just don't run as that can never be true. >> >>> - >>> - return __ipmmu_domain_alloc(type); >>> -} >>> - >