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. >> Somewhere in an init script, we would do this (we know in advance that >> usb1 port2 is the bus/port where we have our pogo-pin USB interface, >> so we can hard-code the path): >> echo 1 > /sys/bus/usb/devices/usb1/1-0:1.0/usb1-port2/quirks >> >> We could try to add ACPI support (just like connect_type), but we >> don't strictly need it for our application. > > Isn't there an "internal" ACPI flag for USB ports, or is that > what connect_type is? Why wouldn't that work here instead? What we may need here is something like "external but non-standard, so we can ignore compatibility constraints when enumerating"... Thanks, -- 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
