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From: Richard Henderson <rth@twiddle.net>
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Date: Tue, 22 May 2018 10:42:21 -0700
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Subject: Re: [Qemu-devel] [PATCH 14/27] iommu: Add IOMMU index concept to
 IOMMU API
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To: Peter Maydell <peter.maydell@linaro.org>, qemu-arm@nongnu.org, qemu-devel@nongnu.org
Cc: patches@linaro.org, Paolo Bonzini <pbonzini@redhat.com>, =?UTF-8?Q?Alex_Benn=c3=a9e?= <alex.bennee@linaro.org>

On 05/21/2018 07:03 AM, Peter Maydell wrote:
> +    /* Return the IOMMU index to use for a given set of transaction attributes.
> +     *
> +     * Optional method: if an IOMMU only supports a single IOMMU index then
> +     * the default implementation of memory_region_iommu_attrs_to_index()
> +     * will return 0.
> +     *
> +     * The indexes supported by an IOMMU must be contiguous, starting at 0.
> +     *
> +     * @iommu: the IOMMUMemoryRegion
> +     * @attrs: memory transaction attributes
> +     */
> +    int (*attrs_to_index)(IOMMUMemoryRegion *iommu, MemTxAttrs attrs);
> +
> +    /* Return the number of IOMMU indexes this IOMMU supports.
> +     *
> +     * Optional method: if this method is not provided, then
> +     * memory_region_iommu_num_indexes() will return 1, indicating that
> +     * only a single IOMMU index is supported.
> +     */

The mispatched callback has been discussed, but would it be equally useful to
simply have a variable here instead of a callback?  Perhaps max_index instead
of num_indexes so that zero-initialization of the structure does the right
thing for existing iommu's.


r~