On Tue, 23 Dec 2014, Peter Chen wrote: > > The Linux USB stack supports turning off port power only under a very > > limited > > set of conditions. For example, if the port is hard-wired or not connected > > at all, > > and if remote wakeup is not required. > > > > Alan, any reasons/limitations we do not support it (by libusb)?
For the same reason we don't allow userspace to interfere with any device: When a kernel driver is in charge of a device, any changes the user wants to make must go through the driver. If users were allowed to make changes to a device without telling the driver, then the driver would not be able to do its job properly. In fact, it's only a coincidence that Deepak's libusb call is able to succeed. Hub control messages use USB_RECIP_OTHER instead of USB_RECIP_INTERFACE, even though they are always meant to go to the hub interface. If the messages used USB_RECIP_INTERFACE then the kernel would prevent libusb from sending the message unless the user program first claimed the hub interface (which would mean unbinding the kernel's hub driver). Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
