On Mon, 8 Apr 2013, Sarah Sharp wrote: > That could work. However, we have to think about future platform power > changes as well. Coming up with a USB specific way to work around the > runtime PM core will hurt us in the long run, if we end up having to > change the runtime PM core for another kernel user. > > Len, Rafael, and Kristen, is there a need from any of the future power > work to have an 'off' mechanism added to the runtime PM core, so that > power/control would have 'on', 'auto', and 'off' options? It currently > only has 'on' and 'auto'. I can't say anything about future power work -- Len, Rafael, et al. will have to speak to that -- but the current design of the runtime PM core doesn't allow for a distinction between "low power" and "no power". As far as the core is concerned, either the device is fully active or else it isn't (i.e., it is suspended). To change this would be a major rewrite. > The kernel is always going to be more conservative about what policies > cause the 'auto' option to turn off USB ports. A Linux distro may want > to override those policies and force the port off, or power off a > misbehaving device for a hard reset. That's why we need an 'off' > extension to power/control to bypass the runtime PM usage counts and > power something off. > > Are there analogous needs for other users of power/control? In fact, some other people have made similar requests. I can't remember the exact contexts now... One of them may have been related to the PCI D4cold stuff. 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
