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1.. SPDX-License-Identifier: GPL-2.02 3============4MHI Topology5============6 7This document provides information about the MHI topology modeling and8representation in the kernel.9 10MHI Controller11--------------12 13MHI controller driver manages the interaction with the MHI client devices14such as the external modems and WiFi chipsets. It is also the MHI bus master15which is in charge of managing the physical link between the host and device.16It is however not involved in the actual data transfer as the data transfer17is taken care by the physical bus such as PCIe. Each controller driver exposes18channels and events based on the client device type.19 20Below are the roles of the MHI controller driver:21 22* Turns on the physical bus and establishes the link to the device23* Configures IRQs, IOMMU, and IOMEM24* Allocates struct mhi_controller and registers with the MHI bus framework25 with channel and event configurations using mhi_register_controller.26* Initiates power on and shutdown sequence27* Initiates suspend and resume power management operations of the device.28 29MHI Device30----------31 32MHI device is the logical device which binds to a maximum of two MHI channels33for bi-directional communication. Once MHI is in powered on state, the MHI34core will create MHI devices based on the channel configuration exposed35by the controller. There can be a single MHI device for each channel or for a36couple of channels.37 38Each supported device is enumerated in::39 40 /sys/bus/mhi/devices/41 42MHI Driver43----------44 45MHI driver is the client driver which binds to one or more MHI devices. The MHI46driver sends and receives the upper-layer protocol packets like IP packets,47modem control messages, and diagnostics messages over MHI. The MHI core will48bind the MHI devices to the MHI driver.49 50Each supported driver is enumerated in::51 52 /sys/bus/mhi/drivers/53 54Below are the roles of the MHI driver:55 56* Registers the driver with the MHI bus framework using mhi_driver_register.57* Prepares the device for transfer by calling mhi_prepare_for_transfer.58* Initiates data transfer by calling mhi_queue_transfer.59* Once the data transfer is finished, calls mhi_unprepare_from_transfer to60 end data transfer.61