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? It sounds like the root cause needs to be figured out here before we allow users to start breaking their systems, right? > The alternative to this approach (user knows best) is to enable LPM for > every device uppon connect and every device which failed this test would > be added to a per-xhci-hcd black list. blacklists are a pain to maintain and if at all possible, not something you ever want to do. > I did not like the auto-test beacause of the additional memory over head > and the additonal time it takes on every plug. How much memory and time is this? thanks, greg k-h -- 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
