linux-kernel - Re: [PATCH 3/4 v5] iommu/fsl: Add iommu domain attributes required by fsl PAMU driver.

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Date:	Sun, 2 Dec 2012 15:03:23 +0100
From:	Joerg Roedel <joro@...tes.org>
To:	Varun Sethi <Varun.Sethi@...escale.com>
Cc:	joerg.roedel@....com, iommu@...ts.linux-foundation.org,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	scottwood@...escale.com, timur@...escale.com
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?

> +	 * 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?

> +struct iommu_stash_attribute {
> +	u32 	cpu;	/* cpu number */
> +	u32 	cache;	/* cache to stash to: L1,L2,L3 */
>  };
>  
>  struct iommu_domain {
> @@ -60,6 +95,14 @@ struct iommu_domain {
>  enum iommu_attr {
>  	DOMAIN_ATTR_MAX,
>  	DOMAIN_ATTR_GEOMETRY,
> +	/* Set the IOMMU hardware stashing
> +	 * parameters.
> +	 */
> +	DOMAIN_ATTR_STASH,
> +	/* Explicity enable/disable DMA for a
> +         * particular memory window.
> +         */
> +	DOMAIN_ATTR_ENABLE,
>  };

When you add implementation specific attributes please add some
indication to the names that it is only for PAMU. DOMAIN_ATTR_STASH
sounds too generic.


	Joerg


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