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The memory controller on NVIDIA Tegra exposes various knobs that can be used to tune the behaviour of the clients attached to it. Currently this driver sets up the latency allowance registers to the HW defaults. Eventually an API should be exported by this driver (via a custom API or a generic subsystem) to allow clients to register latency requirements. This driver also registers an IOMMU (SMMU) that's implemented by the memory controller. It is supported on Tegra30, Tegra114 and Tegra124 currently. Tegra20 has a GART instead. The Tegra SMMU operates on memory clients and SWGROUPs. A memory client is a unidirectional, special-purpose DMA master. A SWGROUP represents a set of memory clients that form a logical functional unit corresponding to a single device. Typically a device has two clients: one client for read transactions and one client for write transactions, but there are also devices that have only read clients, but many of them (such as the display controllers). Because there is no 1:1 relationship between memory clients and devices the driver keeps a table of memory clients and the SWGROUPs that they belong to per SoC. Note that this is an exception and due to the fact that the SMMU is tightly integrated with the rest of the Tegra SoC. The use of these tables is discouraged in drivers for generic IOMMU devices such as the ARM SMMU because the same IOMMU could be used in any number of SoCs and keeping such tables for each SoC would not scale. Acked-by: Joerg Roedel <jroedel@suse.de> Signed-off-by: Thierry Reding <treding@nvidia.com> |
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