On Mon, Aug 26, 2013 at 03:07:25PM -0700, Greg KH wrote: > On Mon, Aug 26, 2013 at 10:45:30AM -0700, Sarah Sharp wrote: > > > > One last thought on this note: We know Windows doesn't have high-res > > timers, and Arjan says asking for a 10 ms delay will produce a delay > > around 17 ms. Since Linux is busy waiting, we may be communicating with > > the device sooner than Windows does. > > What does Windows do for this type of thing? How long do they wait > before reporting an error? We probably need to do the same as they do, > no matter what the spec says. I double checked with the Intel Windows devs, and they say that Arjan is mistaken, and they'll get around 11 ms, just like we do. They say: "The EHCI driver stack applies the 10 ms starting at the point that it sees C_PORT_SUSPEND asserted for the port. The inaccuracy in Windows 8 is generally no more than 1 system clock period late, but it can be delayed by interrupt processing for other devices. I would expect the additional average delay to be no more than 1 ms." They didn't mention waiting for the PORT_RESUME bit to be cleared, like the Linux EHCI driver does. Alan, would you like me to ask them about that? 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
