On Fri, May 25, 2018 at 06:05:16AM +0800, Nicolas Boichat wrote: > On Fri, May 25, 2018 at 12:21 AM, Greg Kroah-Hartman > <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > On Thu, May 24, 2018 at 07:42:00AM +0800, Nicolas Boichat wrote: > >> On Thu, May 24, 2018 at 12:39 AM, Greg Kroah-Hartman > >> <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > >> > On Wed, May 23, 2018 at 10:03:55AM -0400, Alan Stern wrote: > >> >> On Wed, 23 May 2018, Nicolas Boichat wrote: > >> >> > >> >> > The "old" enumeration scheme is considerably faster (it takes > >> >> > ~294ms instead of ~439ms to get the descriptor). > >> >> > > >> >> > It is currently only possible to use the old scheme globally > >> >> > (/sys/module/usbcore/parameters/old_scheme_first), which is not > >> >> > desirable as the new scheme was introduced to increase compatibility > >> >> > with more devices. > >> >> > > >> >> > However, in our case, we care about time-to-active for a specific > >> >> > USB device (which we make the firmware for), on a specific port > >> >> > (that is pogo-pin based: not a standard USB port). This new > >> >> > sysfs option makes it possible to use the old scheme on a single > >> >> > port only. > >> >> > > >> >> > Signed-off-by: Nicolas Boichat <drinkcat@xxxxxxxxxxxx> > >> >> > --- > >> >> > > >> >> > There are other "quirks" that we could add to reduce further > >> >> > enumeration time (e.g. reduce USB debounce time, reduce TRSTRCY > >> >> > to 10ms instead of 50ms as used currently), but the logic is quite > >> >> > similar, so it'd be good to have this reviewed first. > >> >> > >> >> I'm not opposed to the idea in principle, although I don't like your > >> >> implementation because it breaks the original old_scheme_first > >> >> parameter. > >> > >> I don't think it breaks the original parameter? I mean, > >> /sys/module/usbcore/parameters/old_scheme_first is still a global > >> default, while bit 0 of /sys/bus/usb/devices/x/y/z/quirks becomes a > >> port-specific override. > >> > >> >> Let's see what some other people think. > >> >> > >> >> Yours is a rather special case, because you know exactly what device > >> >> will be attached to a specific port. Still, I can see that sort of > >> >> thing happening in constrained and special-purpose settings. > >> >> > >> >> How do you arrange to set the new quirk before the device is > >> >> discovered? > >> > > >> > Yeah, this last question is what I had when looking at this. Or does it > >> > not matter at first boot and only matters for wake-up? > >> > >> It does not matter on boot, we have plenty of time to enumerate the > >> device. We use USB (auto-)suspend and remote wake, so no > >> re-enumeration there either. It only matters on unplug/replug where > >> the device needs to be re-enumerated. > > > > How does this device get unplugged/replugged if it is connected directly > > to the device? > > It is external. Essentially, this is a tablet with a detachable > keyboard/touchpad. The interface between tablet and base is USB, over > pogo pins. The port is non-standard (pogo, not normal USB), and we > fully control the firmware on the base side as well, which allows us > to take shortcuts like this: we know exactly what device will be > connected on that port. Ah, ok, that makes more sense, thanks for the explanation. I'll go queue this up in a bit. 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
