[lkml]   [2014]   [Jun]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH v3 02/10] devicetree: Add generic IOMMU device tree bindings
On 06/26/2014 02:49 PM, Thierry Reding wrote:
> From: Thierry Reding <>
> This commit introduces a generic device tree binding for IOMMU devices.
> Only a very minimal subset is described here, but it is enough to cover
> the requirements of both the Exynos System MMU and Tegra SMMU as
> discussed here:

> diff --git a/Documentation/devicetree/bindings/iommu/iommu.txt b/Documentation/devicetree/bindings/iommu/iommu.txt

> +When an "iommus" property is specified in a device tree node, the IOMMU will
> +be used for address translation. If a "dma-ranges" property exists in the
> +device's parent node it will be ignored. An exception to this rule is if the
> +referenced IOMMU is disabled, in which case the "dma-ranges" property of the
> +parent shall take effect.

I wonder how useful that paragraph is. The fact that someone disabled a
particular IOMMU's node doesn't necessarily mean that the HW can
actually do that; an IOMMU might always be active in HW and always
translate accesses by some master. In that case, the fallback to
dma-ranges wouldn't correlate with what the HW actually does. Perhaps
all we need is to add a note to that effect here?

 \ /
  Last update: 2014-07-01 01:01    [W:0.383 / U:1.080 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site