On Mon, Oct 08, 2012 at 04:03:01PM -0400, Alan Stern wrote: > On Mon, 8 Oct 2012, Sarah Sharp wrote: > > > Some USB 3.0 devices signal that they don't implement Link PM by having > > all zeroes in the U1/U2 exit latencies in their SuperSpeed BOS > > descriptor. Don found that a Western Digital device he has experiences > > transfer errors when LPM is enabled. The lsusb shows the U1/U2 exit > > latencies are set to zero: > > Although this helps with Don's device, do you think there might be > other devices that really do have very short exit latencies and > therefore set the descriptor values to 0? (For U1 at least; maybe not > U2.) In principle these would be the devices best suited to use LPM, > and yet this patch prevents it. I have yet to see a device with the exit latencies set to zero that actually supports LPM. Besides, as you said, the U2 exit latency should be non-zero, so we will enable U2 entry even if the U1 exit latency is zero. That should allow the link to enter a lower power state, even if it takes a little longer than it theoretically could for U1. Sarah Sharp -- 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
