Re: [PATCH v11 20/27] iommu/exynos: allow having multiple System MMUs for a master H/W

From: Tomasz Figa
Date: Fri Mar 14 2014 - 12:13:03 EST


Hi KyongHo,

On 14.03.2014 06:10, Cho KyongHo wrote:
Some master device descriptor like fimc-is which is an abstraction
of very complex H/W may have multiple System MMUs. For those devices,
the design of the link between System MMU and its master H/W is needed
to be reconsidered.

A link structure, sysmmu_list_data is introduced that provides a link
to master H/W and that has a pointer to the device descriptor of a
System MMU. Given a device descriptor of a master H/W, it is possible
to traverse all System MMUs that must be controlled along with the
master H/W.

NAK.

A device driver should handle particular hardware instances separately, without abstracting a virtual hardware instance consisting of multiple physical ones.

If such abstraction is needed, it should be done above the exynos-iommu driver, e.g. by something like iommu-composite driver that would aggregate several IOMMUs. Keep in mind that such IOMMUs in a group could be different, e.g. different Exynos SysMMU versions or even completely different IPs handled by different drivers.

Still, I don't think there is a real need for such abstraction. Instead, related drivers shall be fixed to properly handle multiple memory masters and their IOMMUs.

Best regards,
Tomasz
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