On Wed, 18 Jul 2012, Oliver Neukum wrote: > On Wednesday 18 July 2012 12:40:38 Alan Stern wrote: > > > Oliver, you seem to be arguing both sides of this discussion. You > > But there are more than two sides in this discussion. > > > point out the the power-off operation is too dangerous in general for > > the kernel to do it, and now you say that it's too racy for userspace > > to do it. > > It is too dangerous in general. Therefore it may be safe in particular. > > > Are we to infer that you don't want it to be done at all? > > No, now that I think about it an attribute for the drivers is necessary. > Like drivers have "supports_autosuspend" they also should have > "supports_power_off". In addition it is necessary for ports to have > an attribute in sysfs which allows user space to block power off. > > And it is a bit complicated. Power may be cut, if > > a) a port is internal and unpluggable, or > > b) a port is internal and it's interfaces' drivers set "supports_power_off", unless: > > 1) remote wakeup is requested > 2) user space has blocked it via the new sysfs attribute > 3) USB_QUIRK_RESET_MORPHS is set The same is true for external ports if they are marked as non-removable. For example, consider a compound keyboard/mouse device with a built-in hub. The connections from the keyboard and the mouse to the hub are internal and not removable. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
