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The main issue this driver addresses is that a USB hub needs to be powered before it can be discovered. For discrete onboard hubs (an example for such a hub is the Realtek RTS5411) this is often solved by supplying the hub with an 'always-on' regulator, which is kind of a hack. Some onboard hubs may require further initialization steps, like changing the state of a GPIO or enabling a clock, which requires even more hacks. This driver creates a platform device representing the hub which performs the necessary initialization. Currently it only supports switching on a single regulator, support for multiple regulators or other actions can be added as needed. Different initialization sequences can be supported based on the compatible string. Besides performing the initialization the driver can be configured to power the hub off during system suspend. This can help to extend battery life on battery powered devices which have no requirements to keep the hub powered during suspend. The driver can also be configured to leave the hub powered when a wakeup capable USB device is connected when suspending, and power it off otherwise. Technically the driver consists of two drivers, the platform driver described above and a very thin USB driver that subclasses the generic driver. The purpose of this driver is to provide the platform driver with the USB devices corresponding to the hub(s) (a hub controller may provide multiple 'logical' hubs, e.g. one to support USB 2.0 and another for USB 3.x). Note: the current series only supports hubs connected directly to a root hub (through xhci-plat), support for other configurations could be added if needed. Co-developed-by: Ravi Chandra Sadineni <ravisadineni@chromium.org> Acked-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Ravi Chandra Sadineni <ravisadineni@chromium.org> Signed-off-by: Matthias Kaehlcke <mka@chromium.org> Link: https://lore.kernel.org/r/20210609150159.v12.2.I7c9a1f1d6ced41dd8310e8a03da666a32364e790@changeid Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
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