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? > 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? 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
