Shulou(Shulou.com)06/01 Report--

What this article shares with you is about how the Linux kernel builds the WWAN subsystem to develop the general driver and enhance the expansion ability. The editor thinks it is very practical, so I share it with you. I hope you can get something after reading this article.

Linaro continues to lead the development of the Wireless wide area Network (WWAN) subsystem / framework of the Linux kernel. The framework aims to address at least part of the complexity and heterogeneity of wireless WAN hardware.

The recommended form of the Linux WWAN subsystem is summarized as follows:

This initial version adds the concept of a WWAN port, which is the logical conduit of the modem control protocol. The protocol is exposed to the user through the device, allowing existing tools (ModemManager, ofono.) Straigthforward support in. The WWAN core is responsible for the common part, including character device management, and relies on port-driven operations to receive / submit protocol data.

Since different devices that expose protocols in the same WWAN hardware are not necessarily compatible (for example, two different USB interfaces, PCI/MHI channel devices.) and can be created / deleted in a different order, the WWAN core needs to ensure that all WAN ports contributing to the "whole" WWAN function are grouped under the same virtual WWAN device, depending on the provided parent device (e.g. MHI controller, USB device, etc.).

This initial version is purposefully minimized, basically moving the general part of the previously proposed mhi_wwan_ctrl driver into a general WWAN framework, but the implementation is open and flexible, allowing more drivers to be extended.

The Linux code for this part of WWAN is led by Loic Poulain of Linaro. In addition to studying the general subsystem itself, the main "users" of this subsystem are Qualcomm MHI WWAN control drivers for their PCI Express modems. This new Qualcomm open source WWAN modem driver exposes different modem control protocols / ports to user space. Among the protocols that the driver exposes to user space are AT, MBIM, QMI, QCOM, and FIREHOSE.

This is how the Linux kernel builds the WWAN subsystem to develop general-purpose drivers and enhance scalability. The editor believes that there are some knowledge points that we may see or use in our daily work. I hope you can learn more from this article. For more details, please follow the industry information channel.

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