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SubjectRe: [PATCH 3/4 v4] iommu/fsl: Add iommu domain attributes required by fsl PAMU driver.
On 11/05/2012 05:19:20 AM, Varun Sethi wrote:
> Added the following domain attributes required by FSL PAMU driver:
> 1. Subwindows field added to the iommu domain geometry attribute.
> 2. Added new iommu stash attribute, which allows setting of the
> LIODN specific stash id parameter through IOMMU API.
> 3. Added an attribute for enabling/disabling DMA to a particular
> memory window.
>
>
> Signed-off-by: Varun Sethi <Varun.Sethi@freescale.com>
> ---
> changes in v4:
> - Updated comment explaining subwindows(as mentioned by Scott).
> change in v3:
> -renamed the stash attribute targets
> include/linux/iommu.h | 36 ++++++++++++++++++++++++++++++++++++
> 1 files changed, 36 insertions(+), 0 deletions(-)
>
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index f3b99e1..e72f5e5 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -44,6 +44,34 @@ struct iommu_domain_geometry {
> dma_addr_t aperture_start; /* First address that can be
> mapped */
> dma_addr_t aperture_end; /* Last address that can be
> mapped */
> bool force_aperture; /* DMA only allowed in mappable
> range? */
> +
> + /**
> + * There could be a single contiguous window tha maps the entire
> + * geometry or it could be split in to multiple subwindows.

...or it could be a normal IOMMU that supports arbitrary paging
throughout the aperture.

> + * Subwindows allow for supporting physically discontiguous
> mappings.

...in the absence of arbitrary paging.

> + * This attribute indicates number of DMA subwindows supported
> by
> + * the geometry.

s/indicates number/indicates the number/

> If there is a single window that maps the entire
> + * geometry, attribute must be set to "1". A value of "0"
> implies
> + * that there are 256 subwindows each of size 4K. Value other
> than
> + * "0" or "1" indicates the actual number of subwindows.

No, a value of "0" indicates that this mechanism is not in use at all,
and normal paging is used. PAMU specific things like "256 subwindows"
must not be a default value in a generic API.

In the case of PAMU, if you specify 0 here, the aperture is limited to
1 MiB because that is the limit of PAMU's ability to simulate arbitrary
paging with subwindows, but this is only the limit of one
implementation. It's not part of the API.

-Scott


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