From mboxrd@z Thu Jan 1 00:00:00 1970 From: Scott Wood Subject: Re: [PATCH 3/4 v5] iommu/fsl: Add iommu domain attributes required by fsl PAMU driver. Date: Tue, 4 Dec 2012 12:22:51 -0600 Message-ID: <1354645371.16710.15@snotra> References: Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; delsp=Yes; format=Flowed Content-Transfer-Encoding: 8BIT Return-path: In-Reply-To: (from B16395@freescale.com on Tue Dec 4 05:53:33 2012) Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org To: Sethi Varun-B16395 Cc: Wood Scott-B07421 , Joerg Roedel , "linux-kernel@vger.kernel.org" , "iommu@lists.linux-foundation.org" , "linuxppc-dev@lists.ozlabs.org" , Tabi Timur-B04825 List-Id: iommu@lists.linux-foundation.org On 12/04/2012 05:53:33 AM, Sethi Varun-B16395 wrote: > > > > -----Original Message----- > > From: Wood Scott-B07421 > > Sent: Monday, December 03, 2012 10:34 PM > > To: Sethi Varun-B16395 > > Cc: Joerg Roedel; linux-kernel@vger.kernel.org; iommu@lists.linux- > > foundation.org; Wood Scott-B07421; linuxppc-dev@lists.ozlabs.org; > Tabi > > Timur-B04825 > > Subject: Re: [PATCH 3/4 v5] iommu/fsl: Add iommu domain attributes > > required by fsl PAMU driver. > > > > On 12/03/2012 10:57:29 AM, Sethi Varun-B16395 wrote: > > > > > > > > > > -----Original Message----- > > > > From: iommu-bounces@lists.linux-foundation.org [mailto:iommu- > > > > bounces@lists.linux-foundation.org] On Behalf Of Joerg Roedel > > > > Sent: Sunday, December 02, 2012 7:33 PM > > > > To: Sethi Varun-B16395 > > > > Cc: linux-kernel@vger.kernel.org; > iommu@lists.linux-foundation.org; > > > Wood > > > > Scott-B07421; linuxppc-dev@lists.ozlabs.org; Tabi Timur-B04825 > > > > Subject: Re: [PATCH 3/4 v5] iommu/fsl: Add iommu domain > attributes > > > > required by fsl PAMU driver. > > > > > > > > Hmm, we need to work out a good abstraction for this. > > > > > > > > On Tue, Nov 20, 2012 at 07:24:56PM +0530, Varun Sethi wrote: > > > > > Added the following domain attributes required by FSL PAMU > driver: > > > > > 1. Subwindows field added to the iommu domain geometry > attribute. > > > > > > > > Are the Subwindows mapped with full size or do you map only > parts > > > of the > > > > subwindows? > > > > > > > [Sethi Varun-B16395] It's possible to map a part of the subwindow > i.e. > > > size of the mapping can be less than the sub window size. > > > > > > > > + * This attribute indicates number of DMA subwindows > > supported > > > by > > > > > + * the geometry. If there is a single window that maps > the > > > entire > > > > > + * geometry, attribute must be set to "1". A value of > "0" > > > implies > > > > > + * that this mechanism is not used at all(normal paging > is > > > used). > > > > > + * Value other than* "0" or "1" indicates the actual > number > > of > > > > > + * subwindows. > > > > > + */ > > > > > > > > This semantic is ugly, how about a feature detection mechanism? > > > > > > > [Sethi Varun-B16395] A feature mechanism to query the type of > IOMMU? > > > > A feature mechanism to determine whether this subwindow mechanism is > > available, and what the limits are. > > > So, we use the IOMMU capability interface to find out if IOMMU > supports sub windows or not, right? But still number of sub windows > would be specified as a part of the geometry and the valid value for > sub windows would 0,1 or actual number of sub windows. How does a user of the interface find out what values are possible for the "actual number of subwindows"? How does a user of the interface find out whether there are any limitations on specifying a value of zero (in the case of PAMU, that would be a maximum 1 MiB naturally-aligned aperture to support arbitrary 4KiB mappings)? -Scott