On Tue, 2011-09-06 at 11:26 -0700, Greg KH wrote: > On Tue, Sep 06, 2011 at 08:06:30PM +0200, Sebastian Andrzej Siewior wrote: > > * Greg KH | 2011-09-06 08:27:13 [-0700]: > > > > >> + When a USB2 device which support LPM is plugged to a > > >> + xHCI host root hub which support software LPM, the > > >> + host will run a software LPM test for it; if the device > > >> + enters L1 state and resume successfully and the host > > >> + supports USB2 hardware LPM, it will enable hardware LPM > > >> + for the device and the file shows "enable", otherwise > > >> + it shows "disable". You can write those words to the > > >> + file to enable/disable USB2 hardware LPM manually only > > >> + if the device can perform LPM and the host supports > > >> + hardware LPM. When driver suspend the port into U3 > > >> + state, it will disable hardware LPM first. > > > > > >This file should only show up if the device supports this, not for all > > >devices like this patch has. > > > > > >And why would you not enable this for a device that supports this? > > > > According to Andiry's earlier postings there are some devices which > > support LPM and it works on xhci core from vendor A but it fails on a > > xhci core from vendor B. Another device works fine on both cores. > > As of now the root cause for this anomaly remains unknown. > > Ok, then how would a user, or a distro, know if it was safe or not to > enable this? > The hardware LPM can be enable/disable via sysfs only if the device passed the LPM test, and after that hardware LPM is enabled automatically. User can not force a non-LPM or LPM-test-failed device to enable hardware LPM, it will reject the request and show "operation not permitted", so it's safe. Thanks, Andiry -- 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
