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Date: Mon, 10 Dec 2012 19:00:44 -0600 From: Scott Wood <scottwood@...escale.com> To: Sethi Varun-B16395 <B16395@...escale.com> CC: Wood Scott-B07421 <B07421@...escale.com>, Joerg Roedel <joro@...tes.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>, "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>, Tabi Timur-B04825 <B04825@...escale.com> Subject: Re: [PATCH 3/4 v5] iommu/fsl: Add iommu domain attributes required by fsl PAMU driver. On 12/10/2012 04:10:06 AM, Sethi Varun-B16395 wrote: > > > > -----Original Message----- > > From: Wood Scott-B07421 > > Sent: Tuesday, December 04, 2012 11:53 PM > > To: Sethi Varun-B16395 > > Cc: Wood Scott-B07421; Joerg Roedel; linux-kernel@...r.kernel.org; > > iommu@...ts.linux-foundation.org; linuxppc-dev@...ts.ozlabs.org; > Tabi > > Timur-B04825 > > Subject: Re: [PATCH 3/4 v5] iommu/fsl: Add iommu domain attributes > > required by fsl PAMU driver. > > > > 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@...r.kernel.org; > iommu@...ts.linux- > > > > foundation.org; Wood Scott-B07421; > linuxppc-dev@...ts.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@...ts.linux-foundation.org > [mailto:iommu- > > > > > > bounces@...ts.linux-foundation.org] On Behalf Of Joerg > Roedel > > > > > > Sent: Sunday, December 02, 2012 7:33 PM > > > > > > To: Sethi Varun-B16395 > > > > > > Cc: linux-kernel@...r.kernel.org; > > > iommu@...ts.linux-foundation.org; > > > > > Wood > > > > > > Scott-B07421; linuxppc-dev@...ts.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)? > How about if we say that the default value for subwindows is zero and > this what you get when you read the geometry (iommu_get_attr) after > initializing the domain? In that case the user would know that > implication of setting subwindows to zero with respect to the > aperture size. So it would default to the maximum aperture size possible with no subwindows? That might be OK, though is there a way to reset the domain later on to get back to that informational state? How about finding out the maximum number of subwindows? > Also, should we introduce an additional API like "iommu_check_attr", > which the user can use to validate the attribute value. For example > in case of geometry, the user can fill up the structure and pass it > to the iommu driver in order to verify the aperture and subwindows > field. Doesn't the current API raise an error if you do something unsupported? In any case I don't think making a series of guesses and seeing which ones are accepted is a good substitute for being able to simply read out the relevant parameters. -Scott -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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