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The new way to describe relationship between tunneled ports and USB4 NHI (Native Host Interface) is with ACPI _DSD looking like below for a PCIe downstream port: Scope (\_SB.PCI0) { Device (NHI0) { } // Thunderbolt NHI Device (DSB0) // Hotplug downstream port { Name (_DSD, Package () { ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"), Package () { Package () {"usb4-host-interface", \_SB.PCI0.NHI0}, ... } }) } } This is "documented" in these [1] USB-IF slides and being used on systems that ship with Windows. The _DSD can be added to tunneled USB3 and PCIe ports, and is needed to make sure the USB4 NHI is resumed before any of the tunneled ports so the protocol tunnels get established properly before the actual port itself is resumed. Othwerwise the USB/PCI core find the link may not be established and starts tearing down the device stack. This parses the ACPI description each time NHI is probed and tries to find devices that has the property and it references the NHI in question. For each matching device a device link from that device to the NHI is created. Since USB3 ports themselves do not get runtime suspended with the parent device (hub) we do not add the link from the USB3 port to USB4 NHI but instead we add the link from the xHCI device. This makes the device link usable for runtime PM as well. [1] https://www.usb.org/sites/default/files/D1T2-2%20-%20USB4%20on%20Windows.pdf Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com> Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> |
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README |
README
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.