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diff --git a/Documentation/mhi/topology.rst b/Documentation/mhi/topology.rst new file mode 100644 index 0000000000..dc7799d032 --- /dev/null +++ b/Documentation/mhi/topology.rst @@ -0,0 +1,60 @@ +.. SPDX-License-Identifier: GPL-2.0 + +============ +MHI Topology +============ + +This document provides information about the MHI topology modeling and +representation in the kernel. + +MHI Controller +-------------- + +MHI controller driver manages the interaction with the MHI client devices +such as the external modems and WiFi chipsets. It is also the MHI bus master +which is in charge of managing the physical link between the host and device. +It is however not involved in the actual data transfer as the data transfer +is taken care by the physical bus such as PCIe. Each controller driver exposes +channels and events based on the client device type. + +Below are the roles of the MHI controller driver: + +* Turns on the physical bus and establishes the link to the device +* Configures IRQs, IOMMU, and IOMEM +* Allocates struct mhi_controller and registers with the MHI bus framework + with channel and event configurations using mhi_register_controller. +* Initiates power on and shutdown sequence +* Initiates suspend and resume power management operations of the device. + +MHI Device +---------- + +MHI device is the logical device which binds to a maximum of two MHI channels +for bi-directional communication. Once MHI is in powered on state, the MHI +core will create MHI devices based on the channel configuration exposed +by the controller. There can be a single MHI device for each channel or for a +couple of channels. + +Each supported device is enumerated in:: + + /sys/bus/mhi/devices/ + +MHI Driver +---------- + +MHI driver is the client driver which binds to one or more MHI devices. The MHI +driver sends and receives the upper-layer protocol packets like IP packets, +modem control messages, and diagnostics messages over MHI. The MHI core will +bind the MHI devices to the MHI driver. + +Each supported driver is enumerated in:: + + /sys/bus/mhi/drivers/ + +Below are the roles of the MHI driver: + +* Registers the driver with the MHI bus framework using mhi_driver_register. +* Prepares the device for transfer by calling mhi_prepare_for_transfer. +* Initiates data transfer by calling mhi_queue_transfer. +* Once the data transfer is finished, calls mhi_unprepare_from_transfer to + end data transfer. |