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The E850-96 board has a micro-USB socket and two USB 2.0 host sockets. The USB role (host or peripheral) is selected automatically depending on micro-USB cable attachment state: - micro-USB cable is attached: USB device role - micro-USB cable is detached: USB host role USB can't act simultaneously as a device and a host, because Exynos850 SoC has only one USB controller and there are no external USB controllers on the E850-96 board. So the USB switch chip (specifically TS3USB221A) connects SoC USB lines either to micro-USB connector or to USB hub chip (LAN9514), w.r.t. micro-USB cable attachment state. When USB works in the host role, Ethernet capability becomes available too, as the LAN9514 chip (providing USB hub) also enables Ethernet PHY and Ethernet MAC. Dynamic role switching is done in gpio-usb-b-connector, using current micro-USB VBUS line level as a trigger: - VBUS=high: SoC USB lines are wired to micro-USB socket - VBUS=low: SoC USB lines are wired to USB hub chip In order to make USB host functional when the board was booted with micro-USB cable disconnected, role-switch-default-mode = "host" is used. One can use E850-96 board schematics [1] to figure out how exactly all related USB hardware connections and lines reflect into corresponding device tree definitions. As PMIC regulators are not implemented yet, we rely on USB LDOs being already enabled in the bootloader. A dummy regulator is provided to "usbdrd" vdd nodes for now. [1] https://www.96boards.org/documentation/consumer/e850-96b/hardware-docs/ Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org> Link: https://lore.kernel.org/r/20230825215445.28309-3-semen.protsenko@linaro.org Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.