Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757427Ab2EUROP (ORCPT ); Mon, 21 May 2012 13:14:15 -0400 Received: from avon.wwwdotorg.org ([70.85.31.133]:51272 "EHLO avon.wwwdotorg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754038Ab2EURON (ORCPT ); Mon, 21 May 2012 13:14:13 -0400 Message-ID: <4FBA77E2.4000409@wwwdotorg.org> Date: Mon, 21 May 2012 11:14:10 -0600 From: Stephen Warren User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:12.0) Gecko/20120430 Thunderbird/12.0.1 MIME-Version: 1.0 To: Lucas Stach CC: Thierry Reding , Hiroshi DOYU , linux-tegra@vger.kernel.org, Joerg Roedel , Bharat Nihalani , Vandana Salve , linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/2] iommu/tegra: gart: Reserve iomem resource References: <1337019127-6863-1-git-send-email-hdoyu@nvidia.com> <1337019127-6863-2-git-send-email-hdoyu@nvidia.com> <20120521141152.GA21513@avionic-0098.mockup.avionic-design.de> <4FBA702A.1010203@wwwdotorg.org> <1337619935.1621.13.camel@tellur> In-Reply-To: <1337619935.1621.13.camel@tellur> X-Enigmail-Version: 1.5pre Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1866 Lines: 38 On 05/21/2012 11:05 AM, Lucas Stach wrote: > Am Montag, den 21.05.2012, 10:41 -0600 schrieb Stephen Warren: >> On 05/21/2012 08:11 AM, Thierry Reding wrote: >>> * Hiroshi DOYU wrote: >>>> GART Register/Aperture range should be reserved. >> ... >>>> diff --git a/drivers/iommu/tegra-gart.c >>>> b/drivers/iommu/tegra-gart.c >> ... >>>> + if (!devm_request_mem_region(dev, res_remap->start, + >>>> resource_size(res_remap), dev_name(dev))) { + dev_err(dev, >>>> "failed to reserve GART aperture\n"); + return -EBUSY; + } + >>> >>> I'm not so sure that this is a good idea. If the GART driver >>> requests the GART aperture, then users of the GART aperture (e.g. >>> the DRM driver) will no longer be able to use it. >> >> Presumably the DRM driver would be obtaining access to parts of the >> GART aperture through the GART driver, rather than just grabbing the >> IO region and using it for itself? > > With a TTM-like memory manager the DRM driver will take over the address > space management of the GART aperture. The GART driver is only used to > set up the mappings in the IOMMU. The DRM driver is the one that sets > up/tears down the CPU mappings on demand, so the aperture should be > claimed in the DRM driver. Even if the DRM driver is managing the aperture, I still think the GART driver should claim it. The physical address of the aperture is a property of the GART, so only the GART's resources (and DT node) should contain a representation of where that aperture is. The DRM driver should call into the GART driver to find out where the aperture is, and hence GART is able to claim it without conflict. -- 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/